Illinois
Fertilizer Conference Proceedings
January 28-30, 1991
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R.H Teyker1
The overall objective. of this study is to improve fertilizer N use efficiency of corn. Maintaining fertilizer N in the ammonium form by use of nitrification inhibitors is a proposed strategy for minimizing N loss by leaching or denitrification or both. This strategy will provide an enhanced ammonium supply (EAS) in soils. If an increased amount of ammonium absorption results, the plant must maintain charge balance either by increased. anion uptake or H'' efflux. The latter alternative may lead to problems with proper root growth and functioning and ultimately restrict plant growth and yield.
A field study investigated the influence of genotype and K sources supplying different anions on the nutrition and yield of corn grown under EAS or Ca(NO3)2. Yield, dry matter accumulation, and xylem exudate composition suggests that beneficial effects of KC1 addition under EAS may be due at least in part to the anion chloride. Hybrid differences in nitrate and malate composition of the xylem may point to a potential selection criteria for improving performance on enhanced ammonium regimes.
Producers in the U.S. ComBelt wish to preserve groundwater quality and increase production efficiency. Popular ammoniacal N fertilizers are subject to nitrification and subsequent loss of N by leaching and denitrification. These processes have a negative impact on environmental quality.. .Controlled environment studies indicate that enhanced-NH4 availability improves corn growth and production., Enhanced ammonium supply can be achieved by use of improved nitrification inhibitors and split application of inhibitor treated N fertilizer. A wide range of sensitivity to NH4 exists among plant species, indicating that useful intraspecific variation may exist. Harvey (1939) was the first to note differences among corn inbreds in their response to N form. His results also indicated that seedling dry matter production, under NH4 was a heritable trait. Yield differences in response to enhanced NH4 treatments among modern corn genotypes have also been shown (Below and Gentry, 1987; Pan et al. 1984).
Under enhanced ammonium nutrition, there is an excess of cation over anion uptake. Charge balance is maintained largely by a net efflux of H+ by roots (Raven and Smith, 1976). Rhizosphere acidification that results from this H+ efflux may interfere with normal N metabolism and root growth. The conversion of absorbed NH4 to organic compounds was inhibited in Phaseolis vulgaris (Barker et al. 1966) under EAS in a poorly buffered media. Growth of corn in sand culture decreased as acidity increased from pH7 to pH5 (Magelhaes and Huber, 1989) and corn root systems were shorter and thicker in a Bloomfield fine sand at pH 5.4 compared to limed treatments (Ogango and Teyker, 1990).
As our ability to provide extended NH4 nutrition in the field improves through the use of superior nitrification inhibitors or split N applications or both, a problem of rhizosphere acidification is more likely to develop. The proportion of N supplied as NH4 does not have to be large before media acidification occurs. Non-nodulated soybeans acidified a hydroponic solutions when the ratio of NH4/NO3 supply was above 1/4 (Imsande, 1986). Anion absorption may serve an important charge compensation role as ammonium nutrition is enhanced. Increased uptake of anionic species may offset excess cation uptake and thereby mitigate rhizosphere acidification.
The goal of our research project is to gain a better understanding of ammonium nutrition of corn in soil in order to maximize production efficiency using EAS strategies. Research focuses on overcoming limitations specific to ammonium nutrition through hybrid selection and soil amendments. This paper reports on a field study examining the influence of N and K source on yield, growth and exudates composition of select hybrids.
A 3x2x3 complete factorial field experiment was planted at the Agronomy South Farm on a Drummer silty clay loam (fine-silty, mixed, mesic Typic Haplaquoll) using a randomized complete block design with 6 replicates. Factor A was fertilizer K sources (KC1, K2S04, and KHCO3); factor B, N form [Urea + NI or Ca(NO3),]; and factor C, hybrids (B73xLH51, B73xB79, LH74xLH123). Potassium rates for all forms were 200 lbs K2O/acre. An experimental nitrification inhibitor was provided by Dow Chemical Company. Potassium fertilizers and 130 lbs per acre N were broadcast applied to plots by hand and immediately incorporated. Nitrification inhibitor was sprayed directly onto urea at twice the recommended rate for band application. An additional 70 lbs/acre of N was applied to a trench at the V6 stage to help maintain a treatment difference in form of N available further into the growing season. Corn was planted April 26, 1990 the day after N and K application. This was the second year of a two-year study.
Xylem exudate was collected from the hybrids B73xLH51 and LH74xLH123 at the V4, V6, V10 and R3 growth stages (June 13, June 25, July 14, and August 14, respectively). Three plants per plot were cut and exudate collected with a pasteur pipet following procedures described elsewhere (Teyker et al. 1990).
Exudate was transferred to 10 mL volumetric flasks and brought to volume. Two-.:,mL aliquots of these solutions were diluted three-fold and transferred to sample vials used by a Dionex Automated Sampler. The IC system was a Dionex model 2000i/SP equipped with a conductivity detector and a Dionex 4270 integrator/printer. Samples were loaded onto a 50 μL loop and injected through an AG4A guard column, AS4A separator column and a micromembrane suppressor of eluent conductivity. Ion concentrations of chloride, nitrate, phosphate, malate and sulfate were calculated by regression against authentic standards.
Statistical analyses were performed using the ANOVA and Regression procedures of SAS. Xylem exudate was analyzed by sample date.
Yield results averaged over hybrids (Table 1) show a small but consistent advantage of the EAS treatment. In both years the highest yielding treatment combination was EAS & KC1, while Ca(NO3)2 & KC1 was the lowest (1989) or nearly the lowest (1990) yielding treatment. The other potassium sources, KHCO3.and K2SO4 tended to yield less than the KC1 treatment where EAS was provided.
While hydroponic studies indicate the chlorine requirement for optimal growth is in the micronutrient range, plants accumulate levels of Cl typical of a micronutrient. Fixen et al. (1986) determined that spring wheat response to KCl was due in part to the chloride in KC1. Chloride functions principally in charge compensation and osmoregulation (Marschner, 1986). These functions may assume greater importance when plants absorb a significant proportion of N as NH4.
Chloride is ubiquitous in soils, but since it is readily leached, its concentration in soil surface horizons may become very low, depending on rainfall and soil drainage. Ammonium is relatively immobile and would remain near the surface, especially in many of our more productive, high CEC soils. Sequential sampling of the K x N form experiment in 1990 suggests that a loss of Cl benefit .may have occurred during this particularly wet year (Table 2). The relative advantage of the KCl/EAS- vs. the KCl/Ca(NO3)2-treatment was substantial (9.6 percent) at the V4 sampling, but declined with each successive sample until it reached 1.1 percent at physiological maturity.
The analysis of anions in xylem exudate provided several interesting results (Table 3). Generally, treatment effects were more apparent in the earlier samplings. Coefficients of variation increased slightly with progressive vegetative stages and greatly for the R3 sample.
Xylem exudate C1 concentrations were, consistent with the role. of chloride proposed here. The KCl treatment had a significantly higher Cl concentrtion than the other Ksalt treatments at the V4 and V6 stages, but by V10 there were no K source differences.
The most. surprising result from the exudate analysis was the higher concentrations of nitrate found in the EAS treatment. A tentative explanation is that the unusually wet early spring led to a rapid, substantial loss of fertilizer NO3 by leaching and denitrification whereas the NO3 resulting from delayed nitrification of ammonium in the EAS treatment was more available for uptake at V4 and V6 samplings. Nitrate concentrations from the two N Form treatments were essentially the same in the V10 sampling which was taken 17 days after the 70 lb N/acre split application. The higher concentrations of exudate NO3 in the EAS treatment does not infer that ammonium nutrition was not enhanced. The lower concentration of malate in the exudate of EAS plants probably indicates enhanced ammonium assimilation (Haynes, 1990). The ammonium restriction of root nitrate reduction (MacKown, 1982) could also help account for the higher exudate NO3 concentration found in EAS plants.
Genotype also influenced exudate composition. Hybrid B73xLH51 had higher NO3
and malate concentrations. Hybrid LH74xLH123 had higher SO4 concentrations.
Hybrid 873xLH51 is known to be a consistent responder to EAS and it may be significant
that NO3 and malate occurred in higher concentrations than in LH74xLH123.
The ammonium restriction of nitrate uptake and/or reduction (Jackson et al.
1986) may be less in B73xLH51. It may possess a favorable rate of formation
or partitioning of malate. Malate production or transport in roots may benefit
plants during EAS as 1) an osmolyte, 2) a buffer of xylem pH (Butz and Long,
1979), 3) an anion for cotransport of cations to the shoot, and 4) a substrate
for ammonium assimilation (Dahlbender and Strack, 1986). A greenhouse study
to be reported elsewhere gave consistent results from an analysis of leaf tissue.
Hybrid B73xLH51 had significantly higher NO3 concentrations (22.6
vs 18.6 μmol NO3 g-1 fresh weight), and numerically
greater malate concentrations (7.2 vs .6.7 μ mol malate g-1 fresh
weight) than LH74xLH123.
Taken together, the results suggest that the Cl in KCl performed a special, beneficial role when nitrogen was provided as Urea sprayed with a nitrification inhibitor (an enhanced ammonium supply). Assuming improved nitrification inhibitors and split applications of N can substantially extend the period of EAS, chloride availability could become limiting to roots still absorbing NH4. Any chloride benefit under EAS might in that case be short-lived. These considerations suggest experiments need to investigate the value of a split application of KCl as it interacts with N form.
Hybrids differed in the concentration of ions transported in the xylem, possibly
pointing towards criteria useful in genetically
improving performance under enhanced ammonium supply.
Table 1: Corn yields (average of 3 hybrids) as influenced by N form and source of K
Below, F.E., and L.E. Gentry. 1987. Effect of mixed N nutrition on nutrient accumulation, partitioning and productivity of corn. J. of Fert. Issues 4, 3:79-85.
Butz, R.G., and R.L. Long. 1979. L-Malate as an essential component of corn seedling roots. Plant Physiol. 64:684-689.
Dahlbender, B. and D. Strack. 1986. The role of malate in NH4 similation in cotyledons of radish (Raphanus sativus L.). Plants. 169:382-392.
Fixen, P.E., G.W. Buchenau, R.H. Gelderman, T.E. Schumacher,, J. Gerwing, F.A. Cholick, and B.G. Farber. 1986. Influence of soil and applied chloride on several wheat parameters. Agron. J. 78:736-740.
Harvey, P.H. 1939. Hereditary variation in plant nutrition. Genetics 24:437-461.
Haynes, R.J. 1990. Active ion uptake and maintenance of cation-anion balance: A critical examination of their role in regulation rhizosphere pH. Plant Soil 126:247-254.
Imsande, J. 1986. Nitrate-ammonium ratio required for pH homeostasis in hydroponically grown soybean. J. Exp. Bot. 37:341-347.
Jackson, W.A., W.L. Pan, R.H. Moll, and E.J. Kamprath. 1986. Uptake, translocation and reduction of nitrate. pp 73-108 In: Biochemical Basis of Plant Breeding. Vol. II. Nitrogen Metabolism (C.A. Neyra ed.). CRC Press, Boca Raton, FL.3
MacKown, C.T., W.A. Jackson, and R.J. Volk. 1982. Restricted nitrate influx and reduction in corn seedlings exposed to ammonium. Plant Physiol. 69:353-359
Magelhaes J.R., and D.M. Huber. 1989. Maize growth and ammonium assimilation enzyme activity in response to nitrogen forms and pH control. J. Plant Nutr. 12(81:985-996.
Marschner, H. 1986. Mineral Nutrition of Plants. Academic Press, London.
Ogango, R.O., and R.H. Teyker. 1990. Corn growth and root development under enhanced ammonium supply: Effects of form and rate of lime. J. Fert. Issues (submitted)
Pan, W:L., E.J. Ramprath, R.H. Moll, and W.A. Jackson. 1984. Prolificacy in corns its effects on nitrate and ammonium uptake and utilization Soil Sci. Soc. Amer. Proc. 48:1101-1106.
Raven, J.A. and F.A. Smith. 1976. Nitrogen assimilation and transport in vascular land plants in relation to intracellular pH regulation. New Phytol. 76:415-431.
Teyker, R.H., P.R. Galerani, and E.D. Nafziger. 1990. Analysis of xylem exudate by ion chromatography: Influence of nitrogen and residue management on corn exudate composition. Comm. Soil Sci. Plant Anal. (submitted).
