Redaktor Naczelny – Executive Editor – Mariusz Fotymanawfert.iung.pulawy.pl/zeszyty/pelne/39...

Redaktor Naczelny – Executive Editor – Mariusz FotymaSekretarz Redakcji – Secretary – Kazimierz Kęsik

Rada Konsultacyjna – Advisory Board Pavel Cermak, Havlickuv Brod, Czech RepublicTadeusz Filipek, Lublin, PolandGyorgy Fuleky, Godollo, HungaryWitold Grzebisz, Poznan, PolandJanusz Igras, Puławy, PolandStanisław Kalembasa, Siedlce, PolandJakab Loch, Debrecen, HangaryJan Łabętowicz, Warszawa, Poland, Ewald Schnug, Braunschweig, Germany

Monograph

Effect of fertilizing systems supporting nitrogen use efficiency on maize yield development

Jarosław Potarzycki

Reviewer Jerzy Księżak, Puławy, Poland

Copyright by Polish Fertilizer Society – CIEC

ISSN 1509-8095

Adres RedakcjiZakład Żywienia Roslin I Nawozenia IUNG-PIB

Czartoryskich 8, 24-100 Pulawy, Polande-mail

www: nawfert.pl

Printed: IUNG-PIB Pulawy, 200 copies, B-5

Nawozy i Nawożenie - Fertilizers and FertilizationNr 39/2010

Contents

1. Potarzycki, J. Improving nitrogen use efficiency of maize by better fertilizing practices. Review paper ....................................................................................5

2. Potarzycki, J. Yield forming effect of zinc and magnesium applied as supplements of the NPK fertilizer to maize cultivated in monoculture ...............................25

3. Potarzycki, J. Yield forming effect of combined application of magnesium, sulphur and zinc in maize fertilization ............................................................44

4. Potarzycki, J. Effect of increased input of fertilizers balancing nitrogen on nutrients accumulation by maize at maturity ..................................................60

5. Potarzycki, J. The impact of fertilization systems on zinc management by maize ................................................................................................................78

6. Potarzycki, J. Influence of balanced fertilization on nutritional status of maize at anthesis ............................................................................................................90

7. Potarzycki, J. Yield forming functions of zinc in maize crop Review paper .......109

From the Author

Maize is a crop characterized by a very high yield potential, which is expressed both by biomass production as well as grain yield. Modern varieties of maize are characterized by considerably high resistance to abiotic environmental factors. Therefore, it is widely cultivated in temperate climate zones. This is why the crop is very useful in food and feedstuff production. At present, maize is also considered to be one of the important renewable energy carriers.

Formation of maize yield due to the fixed number of plants per unit field area, already at planting is simplified in comparison to other cereals. This crop development can be split in two periods. The first one extending from tasselling to water stage of kernel’s growth is called the critical window of yield formation. This period which defines the potential grain yield, is significantly affected by external factors, i.e, water and nutrients supply. The second main period of yield development, ripening is to a great extent dependent on the type of variety, classical or stay-green. Accumulation of dry matter by growing cob of a classical variety depends on both, current photosynthesis of leaves as well as on assimilates remobilized from pre-anthesis resources accumulated in stem and leaves. Yield development by a stay-green variety is meanwhile more affected by the photosynthetic activity of current leaves. Therefore, fertilizing strategy of modern maize varieties aimed at the higher greenness of leaves, considered as a plant organ supplying assimilates both to developing kernels and roots, is much more sophisticated.

The most efficient fertilization practices are aimed at balancing nitrogen by other mineral nutrients, especially magnesium, sulfurs and zinc. The date in the literature usually focuses on the specific yield-forming functions of these nutrients. However, they rarely explain how particular nutrients interact in the process of determining the nitrogen supply to maize canopy during critical stages of yield formation and in increasing nitrogen use efficiency.

In the last decade, the author of this monograph has participated in a series of research studies carried on at the Department of Agricultural Chemistry and Environmental Biogeochemistry, University of Life Sciences in Poznań. The aim of these researches was to explain the role of secondary nutrients and zinc in fertilization of maize, supplied with different rates of nitrogen. The scope and subject of the research are innovative not only in Poland but also in the Central-Eastern Europe with similar climate conditions.

In the presented monograph author evaluates nutrient balance status of maize at anthesis and, on this base, tries to predict the final grain yield. Following the assumption that the concentration and distribution of mineral nutrients between plant organs reflect ex post conditions during vegetation, maize nutrient status was also subjected to a post-harvest evaluation (at the stage of full maturity of kernels). This served as the basis for developing the hierarchy of yield forming roles of each micronutrient in different maize fertilization systems.

Zinc fertilization of maize has been a subject of research studies for a long time. However, in this monograph the role of this particular micronutrient in relation to specific critical stages of yield formation of maize is discussed. It has been recognized that the role of zinc is very complex as it depends on both zinc source and accompanying ions as well as on the level of nitrogen nutrition in plants. Thus the study presented in the including papers may become a basis for developing precise recommendations as regards zinc fertilization.


IMPROVING NITROGEN USE EFFICIENCY OF MAIZE BY BETTER FERTILIZING PRACTICES

Review


University of Life Sciences, Poznań, Poland

Abstract

Nitrogen use efficiency (NUE) in maize production in Poland is unsatisfactory, achieving for the period 1992-2008 level of 75 kg grain∙ kg N-1, whereas its maximum is much higher, amounting to 105 kg grain∙ kg N-1. Nitrogen use efficiency, NUE, is an index relating the harvested yield (biomass, grain) to a unit of nitrogen supply and/or assimilated in the harvested yield. Taking into consideration the whole course of plant growth this index can be split into three sub-units: nitrogen uptake efficiency, NUPE, nitrogen utilization efficiency, NUTE, nitrogen remobilization efficiency, NREE. There are two main ways for NUE improvement, breeding new, more efficient varieties and introducing better fertilizing practices. The first strategy requires full understanding the genetic backgrounds of nitrogen uptake by roots and nitrogen functions in increasing radiation use efficiency. The second strategy of NUE improvement relies on maize crop growth environment modification (soil pH, overall fertility level improvement) and on optimizing N rates and on balancing N with other nutrients supply. Band phosphorus application and soil or foliar application of magnesium, sulfur and zinc create fertilizing bases for substantially increase of nitrogen use efficiency. K e y w o r d s: maize, nitrogen use efficiency (NUE), stripe phosphorous application, foliar/soil magnesium application, foliar zinc application

Potential, maximum and actual yields

Potential yield of maize crop based on the amount of radiation is evaluated at the level of 32 t ha-1. Yielding potential of current varieties grown in the U.S. is at the level of 20 t∙ ha-1 [Tollenaar and Lee 2002], but actual yields in the years 2008-2009, were at the level of ca 10,0 t∙ha-1 [FAOSTAT]. The record yield of maize in the U.S., grown in rain-fed conditions, amounted to 23,5 t ha-1. This yield was accomplished by using stay-green maize variety cultivated in monoculture with huge amounts of N, P, K and S fertilizers on fertile soil and by full recycling of post-harvest residues [Reetz 2000].

6Jarosław Potarzycki

In Poland yield potential of grain maize, due to climatic conditions is much lower than in the U.S., reaching 20 t∙ ha-1 [Grzebisz 2008]. Attainable productivity of varieties, grown in assessment trials in the years 2008-2009 was at the level of 10,8 t∙ ha-1 [COBORU 2010]. The actual grain yields, harvested by farmers are much lower, reached in these years on average 6,0 t ha-1 [FAOSTAT, GUS 2010]. According to Księżak [2008] the main factors affecting mostly maize production in Poland are as follows: index of agricultural production area valorization, poultry and pig stocks. Trend of actual maize yields in the period 1992-2008 showed, however an annual rate increase of 99 kg grain∙ ha-1. This positive trend situates Poland in the progressive group of maize producers, indirectly indicating favorable growth conditions for this crop [Hafner, 2003].

In spite of positive trend of yield increment, there is still a wide gap between potential, i.e. attainable yields of maize as recorded by COBORU [2010] for currently grown varieties and actual maize yields in Poland. However, the attainable yield level is corrected by site specifi c conditions explicitly defi ned by supply of water (year effect - considered as a precipitation course) and supply of nitrogen. Both factors defi ne maximum yield of each crop, which are year-to-year variable. In order to calculate maximum yields of maize and yields a gap the concept of the partial factor productivity (PFP) has been applied [Cassman, et al., 2002]. This index expresses the amount of crop productivity (unit/ha) per unit of nutrient applied in fertilizer (Grzebisz et al., 2009). The partial factor of fertilizer nitrogen productivity index (PFPN) in Poland, as averaged over 1986-2008 period was at the level of 75,5 kg grain per 1 kg of applied N fertilizer [FAOSTAT, GUS 2010]. However, its top productivity as evaluated for the fourth quarter (top quartile) was by 36% higher,

Fig. 1. Trends of actual and maximum yields of maize in Poland, years 1992-2008 [FAOSTAT, GUS 2009]; Legend: Y-R – actual yields Y-M – maximum yields

7Improving nitrogen use efficiency of maize by better fertilizing practices

amounting to ca 105 kg grain per kg N. This second index value reflects during the period 1992-2005 growth conditions favorable to maize production. Therefore, it has been used to calculate maximum yields for the 1992-2008 period (Fig. 1). The annual grain yield increase in this period amounted to 99 kg ha-1 but theoretically it could increase at the level of 270 t ha-1. Based on the top unit nitrogen productivity the maximum yield of maize grain in Poland can be set at the level of ca 8,5 t ha-1. At the beginning of the period 1992-2008, the yield gap amounted to 1,35 t ha-1, but it raised up at the end of the period to 3,7 t ha. These two numbers, in spite of increasing yield trend, indicate the occurrence of some factors significantly limiting nitrogen fertilizer productivity. There are some sets of well known factors causing N imbalance, in turn inhibiting growth and maize crop yields in Poland.

Maize is a crop highly tolerable to slightly acid growth conditions, but it is highly sensitive to phosphorus supply, particularly at the beginning of vegetation. The same refers to other nutrients, especially to potassium, but also to magnesium, sulfur, zinc and boron. Soils in Poland are generally poor in available forms of these nutrients. Amounts of main nutrients applied as fertilizers based on yearly country data are highly imbalanced [FAOSTAT]. During the last decade, the N: P2O5: K2O ratio is almost constant at the level of ca 1:0,3:0.40, whereas physiologically established ratio of these nutrients in biomass of high yielding maize crop at harvest amounts to 1:0,45:1,0(1,2) [GUS, 2001; Grzebisz 2009, Grzebisz et al. 2010]. All these growth factors due to imbalanced supply of fertilizer nitrogen are responsible for lowering nitrogen unit productivity (PFPN). The result of this situation is the low yield of grain maize, in additionally showing high-year-to-year variability.

Nitrogen use efficiency, NUE – definition and indices

The nitrogen use efficiency is the main index for evaluation the crop production system related both to production quantity and environment safety [Cassman et al. 2002]. Moll et al., [1982] defined NUE as the yield of grain per unit of available N in the soil (including the residual N present in the soil and the fertilizer). The term available nitrogen encompasses at least, two nitrogen pools, soil nitrogen pool, and fertilizer pool. The first one is difficult for quantitative determination and its measure is usually the amount of nitrogen accumulated by plants grown on plots without N application (control plots or parcels). A good approximation of this pool offers the content of mineral nitrogen Nmin in the soil profile [Pecio et al., 2009]. The second component, fertilizer pool is directly related to the amount of fertilizer nitrogen applied to the currently grown crop during its vegetative season.

According to Moll et al., [1982] the NUE can be divided into two indices: uptake efficiency NupE as the ability of the plant to remove N from the soil in forms of nitrate and ammonium ions and the utilization efficiency NutE as the crop ability to use taken up N to produce grain yield. Author of this review distinguish third


index, nitrogen remobilization efficiency NreE as the contribution of pre-anthesis accumulated N to final grain N yield.

The operational procedures to evaluate indices of nitrogen use efficiency require well defined components such as: plant biomass (B), grain yield (GY), total N uptake (Ntup), total N supply (Ntsp), soil N supply (Nsp), fertilizer N applied (Nf). General algorithms describing basic indices are as follows:

1) NupE = Ntup/Ntsp2) NutE = GY/Ntup

Using experimental data the basic indices can be revaluated into practical algorithms assessing efficiency of N fertilizer nitrogen as presented by the following formulas:3) Agronomic N efficiency, ANE = (GYNf - GYN0)/Nf (kg grain ∙ kg Nf);

Physiological N efficiency, PNE = GYNf - GYN0)/(NtupNf - NtupNN0); (kg grain ∙ kg Nf)

4) Nitrogen apparent recovery, NAR = [(NtupNf - NtupNN0)/Nf] ∙ 100%, or

NAR=PNE/ANE

where: GY- grain yield, kg ha-1;N0- the N non-fertilized (control) plot, Nf- the N fertilized plot.

The third index, nitrogen remobilization efficiency (NreE), includes a set of measures to describe nitrogen economy of maize crop during grain filling period, nitrogen remobilization NR, (kg ∙ ha-1), nitrogen remobilization efficiency NRE, (%), post-anthesis nitrogen gains or losses PANU, (kg ∙ ha-1), efficiency of post-anthesis nitrogen uptake PANUE(%), nitrogen harvest index NHI,(%). The algorithms describing these indices are as follows: 5) NR = Nat - Nhvv

6) NRE = NR/Nat ∙ 100

7) PANU = Nhvtot - Nat

8) PANUE = PANU/Nat ∙ 100

9) NHI = Nhvg/ Nhvtot ∙ 100,

where:

Nat – nitrogen content in plants at anthesis (kg ∙ ha-1), Nhvv – nitrogen content in

vegetative plant organs at maturity (kg ∙ ha-1), Nhvtot – total nitrogen content in plant at maturity, Nhvg – nitrogen content in grain (kg ∙ ha

-1).


Critical stages of maize response to nitrogen supply

Plant growth analysis, based on dynamics of dry matter accumulation, is a very useful method for discriminating the most sensitive stages of maize response to external factors, including supply of nitrogen and other nutrients. The rate of dry matter accumulation by maize plant in the growing season depends on nitrogen supply. As shown in Fig. 2, curves describing the nitrogen uptake rate (NUR) and the crop growth rate (CGR) elevate in two distinct, time-separated stages of maize growth.

The first peak, smaller one, which could be termed as the primary indicator of maize response to nitrogen supply, reveals itself at early stages of this crop growth, i.e., from BBCH17 to 19. Dry matter accumulation rate follows, as presented by the CGR curve, the course of nitrogen accumulation. The second peak of nitrogen uptake, which could be termed as secondary or the major one, occurs at the onset of flowering. Within a period lasting ca 10 days, i.e., from late tasselling (BBCH55-59) till full flowering (BBCH65), the rate of nitrogen accumulation by maize crop doubles itself. However, this elevated maize crop N status is short and temporary, dropping down at the milky stage to former, i.e. pre-anthesis rate of nitrogen accumulation. The CGR course follows the pattern of nitrogen accumulation, reaching a peak at the same stage of maize growth. However, the post flowering rate decline is much

Fig. 2. Dynamics of nitrogen and dry matter accumulation by maize canopy during the course of the growing season [based on Grzebisz at al., 2008a] Legend: NUR – nitrogen uptake rate, CGR – crop growth rate


gentle, ending at the early dough stage of maize growth, i.e. when kernels contain ca 45% dry matter.

Another analytical procedure for discriminating the most sensitive stages of maize response to external factors, including supply of nitrogen and other nutrients is an analysis of the yield components. Maize grain yield is a function of three basic yield components such as the number of cobs per hectare (NC), number of kernels per cob (NKC) and thousand kernels weight (TKW). The main components of NKC are number of rows per cob (NRC) and number of kernels per row (NKR). The component, NC is in a fact established at sowing, assuming one cob per plant, and it can be passed over. The development of other components, results from nitrogen supply in the course of the vegetation season, which in turn depends on other external growth factors (Table 1).

Table 1. Critical stages of structural components of maize yield formation in the course of the growing season (based on Grzebisz, 2008)

Yield structural component

Growth stageBBCH

Factors limiting development of yield components

Nutrient Others

Ears initiation 13-15 N, P, Mg, Zn low temperatures

NRC 16-50 N, K, Mg drought

NKR 50-69 N, K, B, Zn drought

NKC 16-71 N, K, Mg, B, Zn, drought, heat stress

TKW 72-89 N, P, Mg, Zn extremely high temperatures

The maize grain yield development begins since the three leaves stage (BBCH13), initiated by leaves and ears (i.e. cobs) primordia formation. This primary for final yield process is completed at the stage of BBCH15. At this early period of maize plant growth, potential number of leaves and ears with spikelet primordia are established [Viet et al., 1993]. That is probably the main reason of sudden increase of maize plant requirement for nitrogen supply, which takes place in the period extended from BBCH7 to BBCH9 (Fig. 2). As reported by Subedi and Ma (2005) insufficient supply of nitrogen up to the stage of BBCH18 negatively affects diameter of an ear, its length and potential number of kernels per an ear. Potential number of flowers developed by maize ear can be as high as 1000 but number of kernels at full maturity (black stage) is much lower, seldom exceeding 500 per cob. The reduction process begins at early stages of plant growth, during spikelet initiation. The primary yield forming components, number rows per cob, NRC, depends on the efficiency of primordium initial transformation into paired spikelets [Veit et al., 1993]. Therefore, NRC is considered as a highly conservative, inherent genetic characteristic of the


developing maize ear during the season. However, under conditions of severe stress, mainly abiotic (water shortage, low nutrients supply) number of rows is limited, negatively affecting final grain yield [Ritche and Alagarswamy 2003]. The second characteristic of a maize cob, number of kernels per row, NKR, shows, however, a very high response to external factors, such as water and nutrient availability [Potarzycki and Grzebisz 2009].

Kernel number per cob, NKC is a basic component of maize crop yield structure. The decisive period for this element formation begins one week before silking, BBCH51 and finishes four weeks later, i.e. at the blister stage (BBCH71) (Jones et al., 1996). The main, responsible factors in this period are the total sum of physiologically active temperatures, rate of dry matter accumulation, rate of nitrogen supply, rate of water supply. The required sum of temperatures, within this particular period of maize crop development, termed as “critical window”, amounts to 327 oC days (based on t > 8 oC), divided into 227 and 100 oC, before and after silking, respectively [Ritche and Alagarswamy, 2003]. This sum of temperatures allows, with sufficient supply of water and nitrogen, to reach by a maize plant canopy high growth rate [Paponov et al. 2005, Uhart and Andrade 1995, see also Fig. 2). Therefore, any external factor decreasing supply of nitrogen during silking and blister stage in turn decreases the number of kernels per cob.

The last component of the yield structure, thousand kernel weight, TKW, should be considered in the light of the sink/source concept. Sink size defines the ability of developing maize ear, i.e. cob to accumulate nitrogen and assimilates and source the ability of maize vegetative parts to supply of nitrogen and assimilates to the growing cob [Uhart and Andrade, 1995, Cazetta et al. 1999]. The first sub-unit of sink size refers to final number of kernels, established until the end of the blister stage, which depends mostly on water, potassium and boron supply in the “critical window” of maize growth. The second sub-unit of sink size is determined by an individual kernel capacity for dry matter accumulation, which reveals at blister stage. Amount of nitrogen supplied at this stage affects the rate and extent of endosperm cell division and starch granules initiation [Jones at al. 1996]. The source size is responsible both for carbohydrates production during reproductive stages of maize growth, termed as grain filling period and depends on factors responsible for leaf duration and also by rate of nitrogen and assimilates remobilization from vegetative maize parts [Rajcan i Tollenaar 1999, Pommel et al. 2006]. Maize plant well supplied with zinc is able to extend leaves duration, i.e. extending length of leaves assimilation period, which are also capable to increase their own rate of photosynthesis [Guliev et al., 1992].

NUE improvement by breeding new maize varieties

There are two main strategies for improvement nitrogen use efficiency by crop plant. The first one relies on main routs of nitrogen uptake and transformation within the plant. The second one requires an improvement of plant crop growth environment


through optimizing conditions of nutrients uptake, including nitrogen. Therefore, the crop and environment oriented strategy of improvement nitrogen use efficiency is supported by implementation of new maize cultivars, and more efficient management of fertilizer nitrogen applied for maize [Cassman et al. 2002, Hirel et al. 2007].

Breeding studies on maize, conducted both in the tropics and in temperate areas of the World revealed a diversity in N-use efficiency among local, old and new maize varieties, when cultivated on soils poor in nitrogen, or under conditions of low input of external nitrogen [Baenziger et al. 1997, Bertin and Gallais 2000, Ma et al. 1999]. As reported by Paponov et al., [2005] the genotypes selected for high N-use efficiency could sustain the sufficiently high number of kernels per plant under stress conditions. However, field studies, conducted with new, N efficient cultivars, showed a pronounced grain yield reduction, when compared to classical varieties, or when cultivated on soils with high N input. Therefore, taking these negative yield results into account, breeders have established a tolerable yield reduction limit at the level of 35-40% for the N efficient cultivars [Gallais and Coque, 2005].

Maize breeding programs conducted under conditions of low N availability have to take into account three, already mentioned main components of NUE, related to main genetic traits, nitrogen uptake NupE, N assimilation NutE and biomass production and N reallocation into kernels during the filling period, NreE. The first component NupE depends mainly on the maize plant ability to take up soil nitrogen. In this process root system plays a crucial role, especially on soils poor in available nutrients, including nitrogen [Peng et al. 2010]. Hence, efforts of breeders are orienting mainly on modification the maize plant root morphology towards increasing density of plant roots also in deeper soil layers and increasing specific root length (root DM per unit of root length) (King et al., 2003). Other sets of plant modifications refers to increasing biomass production during the vegetative period of maize growth and to N reallocation efficiency during grain filling from vegetative tissues (stem, leaves, roots) to growing kernels [Ta and Weiland 1992]. The first group of traits linked to NutE requires insight into the assimilation mechanizm of N coupled to photosynthesis. However, it is an extremely conservative element of maize plant metabolism, and many breeding programs consider two potentially suitable plant features such as specific leaf area and some enzyme activities. Among many tested enzymes, glutamine synthetase (GS), as deeply involved in many steps of plant nitrogen economy, is nowadays considered as the important genetic trait for explaining variability of N-use efficiency of cultivars grown under different N input (Gallais and Hirel, 2004). Another possibility of NutE improvement relates to modification of N leaf economy, oriented on increasing capture of solar radiation by plant grown under low N input [Hirel at al. 2007].


NUE improvement through nitrogen-balanced management

In the growing season nitrogen requirements are modified by both primary (light intensity, temperature, water and nitrogen supply) and secondary (availability of other nutrients, diseases) factors. An extended study on maize grain production in Canada showed following order of yield limiting factors, weed infestation (27-38%) > lack of pre-plant N application (1-22%) > low plant population density (8-13%) and lack of K (up to 13%), manganese (up to 12%) and zinc (up to 10%) application [Subedi and Ma, 2009].

For maize growers the most important production target is to keep the optimum rates of biomass accumulation by a maize canopy during the growing season, as a prerequisite of full development of yield structure components. Therefore, an agronomical efficient and environmentally friendly maize crop fertilizing system requires the new sets of measures, leading to improvement in N-use efficiency. The holistic strategy of N canopy management should comprise three compatible steps, primary (all measures related to factors controlling maize root growth as a prerequisite of nutrient uptake), basic (all measures related to backgrounds of nitrogen application) and secondary (all measures for effective balancing fertilizer N, addressed mainly to other nutrients supply). In the last few decades, the second and the third set of measures had been deeply worked out by scientists and successfully introduced into farming practice, at least partly.

Nitrogen

The above mentioned three sets of measures should be focused on delivery to maize plant an appropriate amount of nitrogen during each critical stage of yield formation, i.e. keeping nitrogen critical concentration over the course of vegetation. As presented in Fig. 2 the rate of maize canopy growth CGR, depends on the rate of nitrogen accumulation NUR, which in turn is decisive for nitrogen concentration in vegetative tissues. The concept of critical N concentration assumes that at any time of plant vegetative growth a defined N concentration is required, in turn allowing the crop to reach maximum biomass production. The critical N concentration algorithm for maize as developed by Plenet i Lemaire [1999] is presented below:

Nc = 3.4 ∙ W-0.39

where:Nc - critical plant N concentration, % DM;3,4 - nitrogen concentration in plant biomass, when W = 1.0 t ha-1; W - dry matter yield of maize canopy, t ha-1;-0.39 - slope of regression curve

This equation describing so called critical dilution curve informs that throughout maize vegetation and dry matter accumulation the minimum N concentration


decreases in accordance to the power function [Davienne-Barret et al. 2000]. However, the most important part of this function with respect to efficient fertilizing practice in maize crop relates to its development period of biomass below 1,0 t DM ha-1. Therefore, the above equation is, in fact, unsuitable for making any nutritional correction in nitrogen status in maize crop at early stages if its development. It has been calculated that the well-fed maize canopy reaches biomass of about 1 t DM at the stage of BBCH17/19. As described above, at this particular stage, the primary components of maize yield structure are under strong dependence on plant nitrogen nutritional status [Subedi and Ma, 2005; Grzebisz et al., 2008]. Therefore, for full exploitation of maize production potential, any fertilizing efforts oriented on plant N corrections should precede this stage. Hence, the most important nitrogen management target is to detect a critical N concentration at young stages of maize growth up to the BBCH15. This concept as presented in Fig. 3 shows that at early stages of maize growth the measured N concentrations for high-yielding plantations fits fairly well power function. The constant of the developed algorithm is also close to 3.4, i.e. presenting the same level as found by Plenet i Lemaire [1999]. Hence, the critical N concentration in the maize canopy at the stage from the tree to five leaves at very early stages is a new fertilizing target. It must be established at much higher level, for example, from 4.0 to 4.4% as shown in Fig. 3.

Fig. 3. Critical nitrogen dilution curve for maize canopy et early stages of growth [based on Kruczek, 2005a]


The maize fertilizer strategy oriented on NUE improvement should be therefore, supported by an establishment of optimum N rate, type and timing of N fertilizer application and methods of N fertilizer application. The efforts to determine an optimum N rate for maize are complicated, as results from the following theoretically developed algorithm:

FRN = [(Y ∙ Nu) – (Nmin + Nc + Ns)]/NfEwhere:

FRN - N fertilizer rate, kg N ha-1;

Y - yield of grain, t ha-1;

Nu - N specific uptake, kg N t-1;

Nmin - mineral N content in 0-90 cm soil layer, kg N ha-1;

Nc - N soil credit, kg N ha-1;

Ns - soil mineralizable N, kg N ha-1 y-1;

NfE - efficiency of fertilizer N, coefficient < 1,0.

Because of uncertainties of most of the presented algorithm parameters recommended rates of N fertilizers are based mainly on experimental data and so far one of the most important sources of data are production functions [Fotyma E. 1994, Kruczek 2005b]. In spite of limitation of experimental data, they allow making a crude estimation of the optimum N rate ranges for defined growth conditions. However, the experimentally established optimum N rates for high yielding fields are as a rule much lower than frequently applied in farming practice. According to Fotyma (1994) and Kruczek (1997) the optimum N rate, considering soil quality and amount of precipitation during the growing season, should be in the range 90 to 130 kg N ha-1.

The second prerequisite of effective nitrogen application is a proper selection of N fertilizer and its timing. In optimal soil conditions (as indicated by sufficiently high K and P soil fertility level) the best source of nitrogen proved to be ammonium nitrate (Fig. 4). The advantages of this fertilizer are related to nitrate form of nitrogen, easily taken up by maize [Davienne-Barret et al. 2000, Imsande and Touraine 1994]. Nitrogen fertilizers did differ not only in the optimum N rate and final grain yield but also in unit N productivity PFPN. The greatest differences in this index were found at the lowest N rate of 25 kg N ha-1 in the order UR>AN >NPK, while at the optimum N rate PFPN was much lower and ranked in order AN>UR>NPK [Fig. 4]. It must be hence stressed upon conflicting character of PFPN and optimal N rate securing optimal maize yield. As presented in the Fig. 5 the highest values of PFPN were attributed to N lowest rate resulting, however in the lowest yields. As described in the first chapter of this article in the top quartile (for the years1992-2008) the average


PFPN in Poland was at the level of 105 kg grain ∙ 1 kg-1 N. For this particular value

the required N rate amounts to ca 85 kg N ha-1 in order to achieve yield of grain at the level of 85-90% of the yield in maize varieties testing trials [COBORU 2010].

Fig. 5. Partial factor productivity of fertilizer nitrogen (PFPN) as a function of N rates [based on Fig. 4]

Fig. 4. Effect of fertilizer nitrogen type on its optimum rate [based on Kruczek, 2005b]Legend: UR – urea, AN – ammonium nitrate, NPK – complex NPK fertilizer


Phosphorus

Phosphorus is a crucial nutrient for maize plants, particularly in two growth stages. The first reveals before stage BBCH18 (see Fig. 2) and is mostly induced by low soil temperature, that limit P uptake by maize roots. The second, major one reveals during the grain filling period. At that particular stage high demand of maize plant for phosphorus is a result of very high rate of dry matter accumulation by the growing cob [Grzebisz et al., 2008a]. These two critical stages of maize crop response to supply of phosphorus must be taken in consideration in fertilizing system. Young maize plants before the stage of eight leaves(BBCH18), even grown on soil rich in phosphorus, show a high response to fresh applied P fertilizers (Fig. 6).

This response was a reason for developing a sophisticated fertilizing technique, generally known as starter fertilization. It is defined as applications of low P rates in stripes close to seed placement, which in turn brings about higher nutrient concentration in a soil zone penetrated by roots of maize plant (Lu and Miller, 1993). This technique of phosphorus fertilizer application can be successfully used both in poor and P-fertile soils and a part of phosphorus promotes also other nutrients uptake by plants [Kruczek 2005a]. The most important advantage of this technique is better crop performance in the early stage of growth, particularly in unfavorable weather conditions. However, final grain yield response to localized application of P fertilizer depends on many other growth factors, which reveal their activity in the course of

Fig. 6. Effect of phosphorus fertilizer rates on maize seedling biomass at BBCH17 [source of primary data: Lu and Miller 1993 and Kruczek, 2005a]


maize vegetation [Dubas and .Duhr 1983]. Even at the low yield increase, the most important advantage of starter fertilization is lower consumption of P fertilizers and slightly higher content of dry matter in kernels (Tab. 2).

Table 2. Economic evaluation of the strip system of phosphorus fertilizer application to maize crop [Michalski, Kowalik 2007]

Evaluated parameter Size of change Unit cost Financial resultPLN∙ha-1Yield increase, t ∙ ha-1 + 0,2 50 PLN + 100Grain moisture - 1,0% 10 PLN ∙ t-1 ∙ 10 t + 100Total P and K fertilizer application before sowing

Lack of AutumnP and K fertilizing 30-50 PLN + 30-50

Decreased P rate - 30 kg ∙ ha-1

2 PLN kg-1 + 60- 60 kg ∙ ha-1 + 120 Summary - - + 290-370

The better choice for this method of phosphorus application is ammonium phosphate than calcium phosphate [Dachler and Koechl 1995, Kruczek 2005b, Michalski and Kowalik 2007]. For basic (before sowing) fertilization of maize single superphosphate SSP gives better results than triple superphosphate TSP and partially acidulated phosphoric rock PAPR [ Potarzycki 2009] (Tab 3).

Table 3. Effect of phosphorus fertilizer type on nitrogen use efficiency parameters [Potarzycki 2009]

Nitrogen ratekg N ∙ ha-1

Type of P fertilizer 1 Average for N rateControl - NK NPK- PAPR NPK-SSP NPK-TSP

Agronomical efficiency2kg grain ∙ kg N-180 16.7 25.4 29.2 25.9 24.3140 13.6 20.6 21.1 21.1 19.2Average for P fertilizer 15.2 23.0 25.4 23.5 -

Nitrogen recovery %80 54 74 74 72 68140 62 58 56 46 55Average for P fertilizer 68 66 64 50 -

1 Legend: PAPR – partially acidulated phosphoric rock, SSP – single superphosphate, TSP triple superphosphate


Sulfur and magnesium

Maize crop fertilization with magnesium and sulfur is not yet well scientifically worked out. The main reason is a generally low maize crop requirement for both nutrients [Grzebisz 2009]. However, on soils poor in available magnesium, insufficient supply of these nutrients can exert a significant negative effect on nitrogen use efficiency. It is well recognized that increasing rates of fertilizer nitrogen results in NUE declining [Fotyma 2003, Szulc 2010]. Including magnesium and/or sulfur into the maize fertilization program, even on magnesium rich soils may substantially increase nitrogen unit productivity (PFPN) and in turn grain yield (Fig. 7).

Fig. 7. Effect of balanced maize fertilization with nitrogen on grain yield [based on Bar óg and Fr ckowiak-Pawlak, 2008]);

7,6

7,8

8

8,2

8,4

8,6

8,8

9

9,2

9,4

9,6

210 240 260

mazie varieties, FAO number

yiel

d of

gra

in, t

ha-

1

NPKNPK+MgS

Zinc

Maize is considered as crop sensitive to deficiency of boron and zinc [Alloway 2008, Facenko and Lożek 1998, Potarzycki and Grzebisz 2009, Wrońska et al. 2007, 2007a]. The highest relative zinc uptake rate throughout maize growth takes place at the stage of BBCH15-16 [Grzebisz et al., 2008b] preceding the first culmination peak of nitrogen uptake (see Fig. 2). The foliar applied fertilizer zinc causes an increase of the nitrogen uptake rate, and in turn affects dry matter accumulation rate (Fig. 8). The most striking effect of foliar added zinc is, however, the extended period of nitrogen accumulation in the post-anthesis period of maize growth. Yield forming effect of zinc can be therefore, related both to increasing sink and source capacity of maize during reproductive growth. The first one, sink relates to significant increase of the number of kernel per cob (NKC) (Table 4).

Fig. 1. Trends of actual and maximum yields of maize in Poland, years 1992-2008 [FAOSTAT, GUS 2009]; Legend: Y-R – actual

yields Y-M – maximum yields

Fig. 7. Effect of balanced maize fertilization with nitrogen on grain yield [based on Barłóg and Frąckowiak-Pawlak, 2008]);


Fig. 8. Effect of zinc foliar application on dynamics of crop nitrogen uptake rate (CNUR) by maize canopy in the course of the growing season [based on Grzebisz et al., 2008a]

0

100

200

300

400

500

600

700

800

14 17 19 39 59 67 75 83 87 89

growth stages, BBCH scale

CN

UR

, mg

m-2

d-1

0

1

Zn ratekg ha-1

Table 4. Effect of zinc foliar application on maize yield structure components [Potarzycki, Grzebisz 2009]

Zinc rateskg Zn ha-1

Cob length (CL)

Number of rows on the cob (NRC)

Number of kernels in the row (NKR)

Number of kernels in the cob (NKC)

Thousand kernel weight

(TKW)

cm Number g

0 13.88 14.66 27.76 407.0 253.4

0.5 15.37 15.00 29.20 438.0 266.1

1.0 15.72 15.13 31.69 479.5 264.3

1.5 15.19 15.04 29.37 441.7 275.0

LSD 0.05 0.424 n.s. 2.319 34.30 9.74

Its primary reason is probably an extra supply of nitrogen to developing cob, which takes place at young stages, before the BBCH18 [Subedi and Ma 2005]. It finally results in a higher number of kernels per a cob at the blister stage, in turn increasing its demand for carbohydrates supply. The second maize capacity component fulfilling at reproductive growth, source, refers to leaves potential for supplying carbohydrates. The activity of carbonate anhydrase depends on zinc supply [Guliev 1992]. The yield forming effect of zinc on maize source capacity reveals therefore through increasing weight of individual kernels, i.e. higher weight of thousand kernels (Table 4).



As reported by Wrońska at al., [2007a] grain yield of maize crop can be substantially increased by foliar application of zinc in the rate ranging from 0,5 to 1,5 kg ha-1t The optimum time of this nutrient application extends from sowing up to the stage of BBCH 15(16). Zinc supply to maize crop gives the best results at low N rates, i.e. below 100 kg N ha-1 [Wrońska at al.,2007a, Potarzycki and Grzebisz 2009].

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Corresponding author:Dr. Jarosław Potarzycki, University of Life Sciences, Department of Agricultural Chemistry, Wojska Polskiego 71F, 60-625 Poznań, Polande-mail: [email protected]


Fig. 1. Trends of actual and maximum yields of maize in Poland, years 1992-2008 [FAOSTAT, GUS 2009]; Legend: Y-R – actual yields Y-M – maximum yields

Fig. 2. Dynamics of nitrogen and dry matter accumulation by maize canopy during the course of the growing season [based on Grzebisz at al., 2008a] Legend:NUR – nitrogen uptake rate ,CGR – crop growth rate

Fig. 3. Critical nitrogen dilution curve for maize canopy et early stages of growth [based on Kruczek, 2005a]

Fig. 4. Effect of fertilizer nitrogen type on its optimum rate [based on Kruczek, 2005b]Legend: UR – urea , AN – ammonium nitrate, NPK – complex NPK fertilizer

Fig. 5. Partial factor productivity of fertilizer nitrogen (PFPN) as a function of N rates [based on Fig. 4]

Fig. 6. Effect of phosphorus fertilizer rates on maize seedling biomass at BBCH17 [source of primary data: Lu and Miller 1993 and Kruczek, 2005a]

Fig. 7. Effect of balanced maize fertilization with nitrogen on grain yield [based on Barłóg and Frąckowiak-Pawlak, 2008]);


YIELD FORMING EFFECT OF ZINC AND MAGNESIUM APPLIED AS SUPPLEMENTS OF THE NPK FERTILIZER TO MAIZE CULTIVATED IN MONOCULTURE


Poznan University of Life Sciences, Poznań, Poland

Abstract

Field trials with maize (var. FAO 240) cultivated in monoculture were carried out in five consecutive growth seasons from 2003 to 2007. The aim of the work was to evaluate the yielding response of maize fertilized with zinc (NPKZn) or magnesium (NPKMg) at the background of two nitrogen rates: 80 and 140 kg N·ha-1. The average maize grain yield (GY) over years amounted to 9.82 and 10.49 t·ha-1, for nitrogen rates 80 and 140 kg N·ha-1 respectively. Zinc or magnesium supply significantly influenced GY, however in treatments with 80 kg N·ha-1 [NPKZn (10.20 t·ha-1) ≥ NPKMg (9.89) > NPK (9.49)] only. In the treatment with 140 kg N·ha-1, yield increment due to zinc supply amounted to 0.36 t·ha-1. The multiple regression analysis with the choice of the best subset of independent variables (yield components) versus dependent variable (yield) revealed, that GY depended mainly on the thousand kernels weight (TKW), but in the NPK treatment, GY was a resultant of the interaction of all main yield components. TKW generally responded to N rate and Zn supply, but magnesium external supply is important to increase the seasonal yield stability. The results outline a possibility of significant nitrogen rate reduction provided external zinc and/or magnesium supply.Key words: maize, fertilization, nitrogen efficiency, magnesium, zinc

Introduction

Maize is a crop of great economic values, both worldwide and in Poland, due to its versatile use [FAOSTAT 2005, Księżak 2008]. It is characterized by a high yielding potential, defined as a yield of plant variety grown under optimal conditions of water and nutrients supply under conditions of effective weed, pathogens and pests control [Evans and Fisher 1999]. Yielding potential of maize in Poland is in the range from 11 to 13 t·ha-1. However, grain yields actually harvested by farmers are much lower than the yield potential of current varieties, pursuant to unbalanced nutrition, among others [Grzebisz 2008].


The effect of externally supplied nutrients on yield formation is frequently referred to the application of nitrogen fertilizers and the evaluation of nutrient efficiency, beyond nitrogen, based mostly on phosphorus and potassium [Roberts 2008]. Long-term yield stability is a separate matter in the process of potential yield formation. The year-to-year yield variability results not only in the insufficient supply of nitrogen, but also due to the deficiency of secondary nutrients and micronutrients, especially on the light soils. In this context, care must be given by maize growers to magnesium and zinc in order to keep a proper nutritional balance in plant during the growth season [Grzebisz 2008, Lipiński 2005]. Data reported by [Atiken et al. 1999] decidedly show, that magnesium fertilizer application significantly increased grain yield in magnesium-deficient Australian acid soils.

The improvement of mineral nitrogen efficiency after supplementing NPK fertilizers with magnesium has been reported by Rasheed et al. [2004]. These authors applying to the soil 15 kg Mg·ha-1 obtained maize grain yield increment by 1.1 t·ha-1 i.e. by 13%. Under tropical conditions, in a three year field trial with maize, zinc or magnesium applied as sulphate [Abunyewa and Mercer-Quarshie 2004] gained yield increments of 16.5% and 108%, respectively. The effect of zinc on maize grain yield was confirmed in many papers, where zinc has been applied as a foliar top-dressing [Leach and Hameleers 2001, Wrońska et al. 2007, Barłóg and Frąckowiak-Pawlak 2008, Potarzycki and Grzebisz 2009]. The predominance of NPK solid fertilizers in crop production induce to look for possibilities of enriching these fertilizers with magnesium and/or zinc in order to stimulate the yield forming effect of primary nutrients (N, P, K). In practice, NPK fertilizers considered as a carrier to zinc or magnesium can substantially decrease the cost of these nutrients applications.

Monoculture is frequently practiced in maize cropping. However, maize cropped in monoculture is sensitive to many biotic stresses, in turn leading to yield depression due to lower TGW [Kiężak 2010]. In addition, maize cropping system significantly affects N fertilizer efficiency, i.e. nitrogen recovery [Machul and Księżak 2007]. According to Nevens and Raheul (2001), fertilization is one of the factors limiting the negative impact of monoculture on maize yield, and this is related to some particular conditions, nitrogen application among others. Therefore, the hypothesis of zinc and magnesium stimulation in the control of nitrogen efficiency in the yield forming process may be formulated.

The aim of the paper was to assess effects of magnesium and zinc external supply using a solid NPK (as Mg and Zn carrier) on yield forming parameters of maize cultivated in monoculture against a background of two nitrogen rates.

27Yield forming effect of zinc and magnesium applied as supplements of the NPK

Materials and methods

Field’s trials were carried out during five growth seasons from 2003 to 2007 at the agricultural farm located in Nowa Wieś Królewska (52.26o N; 17.57o E, Poland). The long-term static trial was established on a loam soil formed from boulder clay. All chemical analyses were performed according to methods reported by Lityński et al. [1976]. The soil, at the beginning of the experiment was characterized by a slightly acid pH, medium content of available potassium and magnesium and with organic carbon content amounting to 19.0 g·kg-1 (Table 1). Phosphorus content determined by the Egner-Riehm method varied from a medium to high. Among basic agrochemical characteristics the highest year-to-year fluctuation was found for available potassium. The yearly increment of potassium content, finally increasing by ca 10% over the period of five years has been recorded. Mineral nitrogen (N-NH4 + N-NO3) content in the soil layer (0-60 cm) was extracted by using the 0.01M CaCl2 test and further assayed by the FOSS autoanalyzer. Soil bulk density was involved in the calculation of mineral nitrogen content. Each year, the contents of soil mineral nitrogen, as assessed inspring, i.e., just before applying fertilizers, fluctuated within a narrow range, from 53 to 69 kg N·ha-1.

Table 1. Agrochemical properties of arable soil layer at spring before the application of fertilizer and maize sowing (layer 0.00 – 0.30 m)

YearsSoil pH n 1mol·dm3 KCl

Organic carbon a g·kg-1

Available phosphorus b mg P·kg-1

Availablepotassium bmg K·kg-1

Available magnesium cmg Mg·kg-1

Availablezinc d

mg Zn·kg-1

Mineral nitrogenkg N ha-1 e(layer

0-60 cm) 2003 5.8 19.0 57.2 116.2 50.0 6.0 592004 5.9 18.9 55.2 120.4 55.0 5.8 692005 5.7 19.2 61.0 120.4 52.5 6.1 632006 5.8 19.4 55.2 124.5 50.0 5.9 532007 5.6 19.2 61.0 128.7 47.5 6.1 68

a Tiurin method; b Egner-Riehm method; c Schachtschabel method; d 1M HCl; e 0.01M CaCl2

The rainfall distribution for the period of field trials as compared with the long-term (1960-2002) data are listed in Table 2. The highest year-to-year fluctuations in two critical months, i.e., in June and July from the long-term averages were in the years 2004 and 2006. The surplus of precipitation was only in 2007.


Table 2. Rainfalls for the years 2003-2007

Years

Total rainfall in the growth

season, mm

Deviation from

the long-term

mean, %

Months - Deviation from the long-term mean, %

May June July August Septem-ber October

20032004200520062007

181256267357427

- 46 - 23 - 20 + 7 + 28

- 44- 58+121+ 51+ 85

- 58- 24- 55- 43+ 45

+ 8- 53- 1- 90+ 96

- 75+ 15- 2+ 227+ 21

- 74- 51- 50- 24- 28

- 13+ 63- 82+ 9- 34

1the long-term mean = 305 mm

Maize, variety Eurostar (FAO 240), was cropped in monoculture in five consecutive years. A two-factorial field trial, replicated four times was established in a block system design with the following factors:

1. Nitrogen rate:a. 80 kg N·ha-1b. 140 kg N·ha-1

2. Chemical composition of the NPK fertilizer, based on super phosphate:a. NPK with zinc, (NPKZn) + ammonium saltpeter;b. NPK with magnesium, (NPKMg) + ammonium saltpeter; c. NPK fertilizer (NPK) + ammonium saltpeter.

An experimental treatment without nitrogen (absolute control) was also included in four replications, irrespective of the basic experimental design. All treatments were provided annually with phosphorus and potassium, at 26.4 kg P·ha-1 and 99.6 kg K/ha, respectively. Treatments NPKZn and NPKMg received as soil inputs, 1.5 kg Zn·ha-1 (in the form of zinc sulphate) and 15 kg Mg/ha (in the form of magnesium carbonate). All nutrients were incorporated in one fertilizer granule. This is a reason for not including the costs of separate broadcasting of zinc and magnesium to the total costs of fertilizer application. All fertilizers were applied just two weeks before maize sowing, in the third decade of April. The yield of grain was determined from an area of 24 m2 (two central rows of 16 m length) at technological maturity of grains (ca 70% dry weight basis). Total grain yields were adjusted to 14% moisture content. At harvest each plant sample was partitioned into sub-samples of grain and straw (including leaves, stems, cob covering leaves and cob cores) and then dried (65oC). The following components of yield structure were estimated: thousand kernels weight (TKW), number of rows on the cob (NRC), number of kernels in the row (NKR), and number of kernels in the cob (NKC). A sample of 20 cobs for each treatment was used for determination the components of yield structure.


The harvest index (HI) expressed as the percentage share of grain yield (GY) in the total aboveground biomass (Bt) was determined using the following formulas:

HI = (GY/Bt) x 100% (%)

the nitrogen agronomical efficiency (NAEGY) for grain yield:

NAEGY = (GYN – GYac)/D (kg·kg-1 )

the nitrogen agronomical efficiency (NAETB) for total biomass:

NAETB = (TBN – TBac)/D (kg·kg-1)

where:GYN – grain yield of nitrogen fertilized treatments, kg·ha

-1

GYac – grain yield of the absolute control, kg·ha-1

TBN – total biomass of nitrogen fertilized treatments, kg·ha-1

TBac – total biomass of the absolute control, kg·ha-1

D – nitrogen rate, kg N·ha-1The experimentally obtained data were subjected to conventional analysis

of variance. The least significant difference values (LSD at P = 0.05) were used to estimate the differences of mean values. The simple regression was applied to establish relationships between plant characteristics [Malec and Caliński 1973, STAT_LK©].

Results and discussion

In Poland, it has been evaluated that the yielding potential of actually cropped maize variety ranges from 10 to 13 t·ha-1 [Grzebisz 2008]. Yields harvested in the own investigations were relatively high and varied between 9.82 and 10.49 t·ha-1, for the rates 80 and 140 kg N·ha-1 respectively (Table 3).

The applied mineral supplements, i.e., zinc or magnesium has significantly increased yields of maize, but in dependence on the nitrogen rate (Figure 1). Maize crop fertilized with 80 kg N·ha-1 responded significantly to both nutrients, showing, however, higher yield increase under zinc application. On the plot fertilized with 140 kg N·ha-1 only tendency for zinc effect was observed.

The analysis of grain yield trend throughout the whole experimental period shows its significant decrease starting in the fourth year (Table 3). The yield decreased progressively up to the last year of the study, despite very favorable moisture conditions during the 2007 vegetative growth period. According to Berzsenyi et al. [2000], data from a long-term field trial showed that grain yields of maize were as a rule lower under monoculture, particularly in years characterized by dry winter and rainfall deficiency in summer. Indeed, yield decrease, which was observed in 2006, was probably induced by water deficiency in June and July (Table 2). In this period,


maize usually builds up high aboveground biomass and hence requires more water and adequate nutrients [Otegui et al. 1995, Boye and Westgate 2004].

Table 3. Aboveground maize biomass

Experimental factor

Biomass, t·ha-1Harvest index (HI), %Stem Leaves Grain

Cob covering leaves

Cob cores Total

Years 20032004200520062007

5.245.384.876.423.91

2.622.333.493.423.08

10.7110.1911.699.988.21

0.530.851.160.930.88

1.251.411.611.441.32

20.3420.1522.8222.2017.45

50.049.551.245.047.5

LSD 0.55** 0.34** 0.31** 0.14** 0.13** 0.90** 2.0**

N rate, kg N·ha-1 80140

5.025.30

2.963.01

9.8210.49

0.820.92

1.361.45

19.9921.17

49.349.6

LSD n.s. n.s. 0.20** 0.09* 0.09* 0.57** n.s.

Fertilizer type NPKZnNPKMg

NPK

5.175.025.30

2.952.913.13

10.4110.139.93

0.860.810.95

1.441.361.43

20.8220.2320.73

50.250.148.0

LSD n.s. n.s. 0.17** 0.11* n.s. n.s. 2.0**

Absolute control 3.72 2.07 7.37 0.59 1.12 14.9 49.5 ** P


The highest yield of maize grain was harvested in the 2005 year. High precipitations in the May and sufficient amount of rainfalls in July as well as August 2005 have boosted maize development and the production of high grain yields. Moreover, this particular year was characterized by a great differentiation of the tested fertilizer’s effects. It appears that the efficiency of NPK fertilizers supplemented with zinc or magnesium depended on weather course during the vegetative growth of maize. This was supported by the fact that natural levels of zinc and magnesium in soils remained relatively unchanged for the consecutive years of investigations (Table 1). Average grain yields for the period 2003 - 2006 surpassed 10 t·ha-1. As reported in Table 2, higher rainfalls (i.e., 192 mm) were recorded in 2005, particularly in the vegetative period of growth. The remaining years were characterized by a precipitation fluctuating within the range 111 – 128 mm. In the year 2005, mean yield increment as induced by zinc application amounted to 0.88 t·ha-1 (0.28 – 0.60 for the remaining years), and by magnesium 0.55 t·ha-1 (0.05 – 0.23, respectively). It may be concluded that the amounts of rainfalls were the key factor that regulated the yield forming effect of zinc and magnesium. According to Barłóg and Frąckowiak-Pawlak [2008], year-to-year variable weather conditions affected much less the variability of the maize aboveground biomass, in comparison to grain yield. In the presented experiments, the total biomass and all vegetative plant parts and the harvest index (HI) varied significantly during experimental years (Table 3). However, yields of grain showed much lower fluctuations than those observed for yields of leaves and stems. It is indicated by the coefficients of variation (CV), amounting to 13.1% for grain, 23.9% for stems and 25.5% for leaves (number of observations = 120). The highest biomass of stems in 2006 with the simultaneously lowest grain yield as compared to years, 2003-2005 was recorded. This observation may be explained by a disturbance in assimilates translocation from stems to cobs during the period of grain filling due to the excess of precipitation in August. This thesis is corroborated by much lower thousand kernels weight (see Table 4).

The effect of applied fertilizer on maize parts biomass was different.(Table 3). The rise of nitrogen rate from 80 do 140 kg/ha led to a significant increase of grain yield (at P


Table 4. Yield structure components of maize

Experimental factorThousand

kernels weight (TKW) g




Years 2003 2004 2005

20062007

309313319288264

16.415.315.315.616.0

30.729.432.331.527.2

503450493491434

LSD 8** 0.4** 1.5** 25*

N rate kg N·ha-1 80140

296302

15.715.8

29.730.6

466481

LSD 5** n.s. n.s. n.s.

Fertilizer type NPKZnNPKMg

NPK

303298295

15.715.715.7

30.430.230.1

476474473

LSD 6* n.s. n.s. n.s.

** P NPKMg = NPK (10.37)]. It can be therefore, concluded that zinc as a mineral additive to the NPK basic fertilizer reveals its yield forming effect,


irrespective of the amount of mineral nitrogen. In farming practice this conclusion clearly indicates an opportunity to make a significant decrease of the applied rates of fertilizer nitrogen, provided zinc supply is at optimum. The methods of zinc application are of secondary importance, as comes out from the own study and other reported data. In the conducted study externally applied magnesium, considered as the NPKMg fertilizer supplement, revealed its yield forming effect only under a condition of lower N rate. This phenomenon can be related to the physiological function of Mg2+, which is responsible for nitrate anions uptake by plant roots from soil solution [Jones and Huber 2007]. Grain yield increment due to the effect of higher N rate at the background of lower N rate can be presented in ascending order: NPK (+0.88 t·ha-1) > NPKZn (+0.65) > NPKMg (+0.48). The presented order indirectly corroborates the thesis of magnesium specificity in maize nitrogen management.

Similarly, to grain yield, it was found that the year-to-year variability affected also all components of yield structure (Table 4). However, the seasonal variability was much more important for thousand kernels weight (TKW) than for the number of kernels per cob (NKC). The TKW variability should be attributed to weather conditions, particularly to the sum of temperatures, which modifies not only the photosynthetic activity of plants, but also the distribution of assimilates between vegetative parts and grains [Maddoni et al. 1998]. Thousand kernels weight (TKW) was the sole yield component, which varied respectively with the type of NPK fertilizer and nitrogen rate. It appeared that this component was mostly influenced by nitrogen rate (P


Table 5. Relationships between yield of grain and components of yield structure expressed as correlation coefficient, n=20

Nitrogen rate

Fertilizer type

Yield structure component

Thousand kernels weight

(TKW)




80 kg N·ha-1

NPKZn 0.72*** 0.16 0.32 0.28

NPKMg 0.59** -0.29 0.36 0.27

NPK 0.70*** -0.15 0.35 0.27

140 kg N·ha-1

NPKZn 0.77*** -0.28 0.68*** 0.60**

NPKMg 0.64** -0.04 0.28 0.28

NPK 0.75*** -0.18 0.36 0.33 ** P


field trials indicate, that for treatments with the lowest nitrogen rate (80 kg N ha-1) and NPKZn as well as NPKMg treatments, the TKW was the variable, which the best shaped the final yield of grain (Table 6). This was confirmed by the values of mean square error (MSE), decreasing along with rejecting subsequent variables. In the case of both NPK treatments, the developed models should consider all three analyzed variables, since the removing of each subsequent variable significantly reduced R2 values. Therefore, similarly for the treatments with nitrogen rate of 140 kg N·ha-1 and NPKZn as well as NPKMg combinations, the best subsets were determined and involved two variables, respectively TKW and NKR or TKW and NRC (these parameters are underlined in Table 6).

Table 6. Multiple regression analysis with the choice of the best subset of independent variables (yield components) versus dependent variable (yield), mean for years 2003-2007, n=20

Nitrogen rate

Fertilizer type

Number of independent variables

Coefficient of determination

R2

Mean square error (MSE)

Best subset of independent variables*

80 kg N·ha-1

NPKZn321

52.0351.9851.59

0.9320.8770.835

TKWTKWTKW

NRC NKRNKR

NPKMg321

35.7235.3934.37

1.2311.1641.117

TKWTKWTKW

NRCNRC

NKR

NPK321

55.2752.5449.07

0.6650.6640.673

TKWTKWTKW

NRCNRC

NKR

140 kg N·ha-1

NPKZn321

65.4065.3958.83

0.7680.7230.812

TKWTKW

TKW

NRC NKRNKR

NPKMg321

47.4546.9740.82

1.1081.0531.110

TKWTKWTKW

NRCNRC

NKR

NPK321

62.7759.6756.86

0.9020.9190.929

TKWTKWTKW

NRCNRC

NKR

* TKW - Thousand kernels weight; NRC - Number of rows on the cob; NKR - Number of kernels in the row

According to literature data effects of zinc on grain yield and its structure components is diversified throughout maize growth stages. Zinc as a nutrient required


Figure 2. (a and b). Relationship between total biomass and grain yield of maize

GY = 0.4897TB + 0.032R2 = 0.61

6789

1011121314

16 18 20 22 24 26

Total biomass (TB), t ha-1

Gra

in y

ield

(GY

), t h

a-1 a. 80 kg N ha-1

GY = -0.0664TB2 + 3.2416TB - 28.048R2 = 0.74

GYmax = 11.52; TBopt. = 24.416789

1011121314

16 18 20 22 24 26

Total biomass (TB), t ha-1

Gra

in y

ield

(GY

), t h

a-1

b. 140 kg N ha-1

for auxin synthesis, stimulates the development of the root system at the 6 – 12th leaf growth stage and hence increases water uptake along with nutrients, particularly nitrogen. Cob initiation and the number of rows in the cob (NRC) are being formed during this period [Grzebisz 2008]. Results of the current trial revealed, that the NPK fertilizer supplemented with zinc did not influence this component of yield structure. This may be attributed probably to the applied NPK fertilizer based on super-phosphate and the time required for releasing zinc from granules. Final yield of maize grain, however, is significantly affected by the yield components shaped at anthesis and grain filling. The final number of grains in the cobs is also a resultant of the pollen vitality at anthesis, and this feature is partly controlled by zinc supply [Westgate et al. 2003]. The yield forming effect of zinc is being best manifested at post-anthesis maize growth, i.e., grain filling period. Zinc by enhancing the carbonic anhydrase synthesis and further extending physiological activity of leaves supports the photosynthesis efficiency [Gibson and Leece 1981, Guliev 1992].

Figure 2. (a and b). Relationship between total biomass and grain yield of maize


This micronutrient controls the synthesis and accumulation of starch in the grains and in turn affects the thousand kernels weight (TKW), as presented in this study.

With respect to final grain yield, one of the main important relationships concerns its dependency on total plant biomass [Sinclair et al. 1990]. The presented data showed the significant effect of the applied nitrogen rate on the best fitted regression model. In the treatment fertilized with 80 kg N·ha-1, this relationship was best described by the linear regression model (Figure 2a), whereas in the case of 140 kg N·ha-1, by the quadratic regression one (Figure 2b). As presented above, the TKW was the key component of yield structure describing the final yield of grain. Therefore, it was important to find out its dependency on stem and/or leaves biomass. Stem is considered as a storage of assimilates from pre-anthesis maize growth and the leaves are responsible for current assimilates delivery to growing kernels [Rajcan and Tollenaar 1999]. As reported by Maddonni et al. [1998], individual mass of the maize kernel is significantly related to post-anthesis maize biomass growth, i.e., to current photosynthetic plant efficiency. The relationships, between grain yield (dependent variable) and biomass of leaves or stems (independent variables), as listed in Table 7, have been described by quadratic regression models. This model allows calculating some sets of parameters, such as an optimum plant biomass and concomitant maximum TKW. Among studied plant parts, the crucial for reliable TKW diagnosis was the biomass of stems. Its optimum has been significantly affected by both experimental factors and ranged from 5.24 t·ha-1 for the NPK + Mg treatment and 5.74 t·ha-1 for the NPK one fertilized with 140 kg N·ha-1. Biomass of stems above the developed range resulted in TKW decrease. Based on the obtained range it can be explained much lower TKW as found in 2006. In this particular year, the stem biomass reached 6.42 t·ha-1, i.e. above the threshold range, which resulted in an average grain yield ca 9% lower in comparison to the 2003-2005 average.


Tabl

e 7.

Reg

ress

ion

mod

els o

f tho

usan

d ke

rnel

s wei

ght (

TKW

) as

a fu

nctio

n of

bio

mas

s of l

eave

s (L)

or s

tem

s (S)

Nitrogen

rate

Fertilizer

type

L x TK

WS x TK

W

80

kg N·ha-1

NPK

Zn-

TKW = -23.875S

2 + 256.27S - 369.79; n = 5

R2 = 0.83; TKW

max. = 318; S

opt. = 5.37

NPK

Mg

TKW = -92.44L2 + 495.08L - 344.72; n = 5

R2 = 0.84; TKW

max = 318; L

opt. = 2.68

-

NPK

-TK

W = -26.305S

2 + 277S - 421.3; n = 5

R2 = 0.99; TKW

max. = 308; S

opt. = 5.26

140

kg N·ha-1

NPK

Zn-

TKW = -20.565S

2 + 220.96S - 272.96; n = 5

R2 = 0.98; TKW

max. = 321; S

opt. = 5.37

NPK

Mg

-TK

W = -34.574S

2 + 362.47S - 626.63; n = 5

R2 = 0.80; TKW

max = 324; S

opt. = 5.24

NPK

-TK

W = -15.206S

2 + 174.66S - 181.63; n = 5

R2 = 0.98; TKW

max. = 320; S

opt. = 5.74


For leaves biomass only one significant relationship was found and refers to the NPKMg treatment fertilized with 80 kg N·ha-1. In this particular case the optimum biomass of leaves amounted to 2.68 t·ha-1, but its long-term average as shown in the Table 3, was slightly higher, amounting to 2.91 t·ha-1. Therefore, it can be concluded, that maize fertilized with magnesium shows a tendency to produce biomass of leaves in excess, in turn negatively affecting TKW and finally grain yield. On the base of this data, it is necessary to verify the process concerning yield forming functions of magnesium in stay-green maize varieties. The effect of magnesium on biomass of maize leaves is well documented. The main function of leaves during post-anthesis growth of maize is not only to absorb CO2, but even more important is to increase the rate of assimilates transfer to developing kernels [Pommel et al. 2006]. It has been, however, documented, that leaves are highly conservative plant parts with respect to dry matter decline during post-anthesis maize growth, probably due to the insufficient amount of nutrients enhancing carbohydrate and nitrogen remobilization [Fischer 2007]. As reported by Potarzycki (2004), winter wheat fertilized with copper showed the predisposition to increase nitrogen remobilization from leaves during the grain filling period.

Seasonal variability of maize yields, both vegetative – total biomass (TB) and generative - grain (GY) may be partly explained by applying two respective indices of nitrogen agronomical efficiency (NAE). According to Johnson et al. ([997] and Kruczek [2000], agronomical efficiency of fertilizer nitrogen decreases with increasing its rates. This general rule was totally corroborated by the data of both studied parameters, but showing year-to-year variability (Table 8). The year-to- year variability of NAEGY indices as explained by the coefficient of variability (CV) showed dependency on the NPK fertilizers. The average value of CV for the tested treatments showed a tendency to decrease in the following order: NPKZn = NPK (CV = 30%) > NPKMg (23%). The found the order stresses on the importance of magnesium external supply in creating seasonal yield stability.

Table 8. Nitrogen agronomical efficiency for grain yield (NAEGY) and for total biomass (NAETB), kg·kg

-1

Nitrogen rate

Fertilizer type

Consecutive years Mean2003 2004 2005 2006 2007

80 kg N·ha-1

NPKZn 36.01/50.62 20.7/62.4 45.9/84.2 36.5/73.9 30.5/66.4 33.9/67.5NPKMg 30.4/ 42.7 23.4/76.6 42.5/59.0 33.5/62.1 27.9/68.4 31.5/61.8NPK 29.1/37.2 18.3/79.6 28.6/66.4 30.8/71.5 25.9/58.1 26.5/62.6 Mean 31.8/43.5 20.8/72.9 39.0/69.9 33.6/69.2 28.1/64.3 30.7/63.9

140 kg N·ha-1

NPKZn 23.9/32.4 18.1/ 45.2 29.7/58.7 29.2/56.7 19.1

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