Mark M. Alley

A manual colorimetric procedure for measuring ammonium nitrogen in soil and plant Kjeldahl digests

Abstract The measurement of NH4+‐N in soil, and plant digests is one of the greatest needs in laboratories conducting agricultural and environmental research. Many laboratories do not have access to automated equipment for colorimetric analysis of soil and plant digests. The objective of this research was to modify an automated colorimetric analysis procedure for determining NH4+‐N in soil and plant digests for manual use, and compare the proposed technique with the standard distillation‐titration technique. The modified procedure is based on the color reaction between NH4 +‐ and a weakly alkaline mixture of Na salicylate and a chlorine source in the presence of Na nitroprusside. Wavelength scans indicated a very well defined peak for determinations at 650 nm. Time scans showed that color development in the manual procedure was rapid, 12 to 40 minutes depending on temperature, and that the color development remained stable for at least 120 minutes. Regression analysis of the results from 18 soil and 20 pl...

Plant Density and Hybrid Impacts on Corn Grain and Forage Yield and Nutrient Uptake

ABSTRACT Corn (Zea mays L.) production recommendations should be periodically evaluated to ensure that production practices remain in step with genetic improvements. Since most of the recent increases in corn grain yield are due to planting at higher densities and not to increased per-plant yield, this study was undertaken to measure the effects of plant density and hybrid on corn forage and grain yield and on nutrient uptake. Plant density (4.9, 6.2, 7.4, and 8.6 seeds m−2) and hybrid relative maturity (RM) [early (108 day RM); medium (114 day RM); and late (118 day RM)] combinations were evaluated over five site-years under irrigated and non-irrigated conditions. The interaction of hybrid with plant density was never significant for grain, stem, or leaf biomass. The latest RM hybrid out-yielded the medium and early hybrids by 550 and 1864 kg ha−1, respectively. Grain yield was highest at 8.6 plants m−2. Total stem yield was also greatest at the highest plant density but by only 340 kg ha−1 more than at 7.4 seeds m−2. Based on grain yield response over sites, the estimated optimum density was 7.6 seeds m−2, which is 0.7 seeds m−2 higher than the current recommendation at this average yield level (11.5 Mg ha−1). Grain nitrogen (N), phosphorus (P), and potassium (K) uptakes were highest for the medium RM hybrid. Nutrient uptake levels varied by planting density, with the lowest levels observed at the lowest and highest plant densities. At 4.9 seeds m−2, the reduced uptake is explained by lower biomass yields. At the 8.6 seeds m−2 rate, N and K levels may have been lower due to dilution.

Cation exchange capacity measurements

Abstract Soil cation exchange capacity (CEC) measurements are important criteria for soil fertility management, vaste disposal on soils, and soil taxonomy. The objective of this research was to compare CEC values for arable Ultisols from the humid region of the United States as determined by procedures varying widely in their chemical conditions during measurement. Exchangeable cation quantities determined in the course of two of the CEC procedures were also evaluated. The six procedures evaluated were: (1) summation of N NH4OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus BaCl2 ‐ TEA (pH 8.0) exchangeable acidity; (2) N Ca(OAc)2 (pH 7.0) saturation with Mg(OAc)2 (pH 7.0) displacement of Ca2+; (3) N NH4OAc (pH 7.0) saturation with NaCl displacement of NH4 +; (4) N MgCl2 saturation with N KCl displacement of Mg2+; (5) compulsive exchange of Mg2+ for Ba2+; and (6) summation of N NH4OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus N KCl exchangeable AJ. The unbuffered procedures reflect the pH dependent CEC ...

WINTER HULLESS BARLEY RESPONSE TO NITROGEN RATE AND TIMING AND FOLIAR PHOSPHORUS

Hulless barley (Hordeum vulgare L.) is higher in energy density and protein than hulled barley but management recommendations for this new crop are lacking. Intensively managed hulled barley receives two spring nitrogen (N) applications. How this will affect winter hulless barley yield and protein is unknown. ‘Doyce’ hulless barley was planted following corn (Zea mays L.) at seven site-years in the Coastal Plain of Virginia from 2005 to 2007. Spring N was applied as urea ammonium nitrate (UAN, 30% N) in an incomplete factorial of treatments at Zadoks growth stage (GS) 25 and 30 broadcast at rates of 0, 45, 67, and 89 kg N ha−1. Six kg ha−1 of phosphorus (P) was foliar applied at GS 30 to treatments receiving 45:45 (45 kg N ha−1 at GS 25 and 45 kg N ha−1 at GS 30) and 45:67 N splits. Additionally, 34 kg N ha−1 as UAN was applied at GS 45 to treatments previously receiving either 45:45 or 45:67. Grain test weight increased with increasing N rate verifying that high spring N rates can be applied without negatively impacting grain test weight in this environment. Grain protein responded positively to increasing N rates as additional N at GS 45 increased protein by 0.7%. To maximize yields, 112 kg N ha−1 applied as 45 kg N ha−1 at GS 25 and 67 kg N ha−1 at GS 30 was necessary. Supplying the majority of spring N need at GS 30 proved important to matching barley N demand and achieving high yields.

Using Synthetic Chelating Agents to Decrease Phosphorus Binding in Soils

Abstract Most acid soils have a high capacity to bind phosphorus (P) strongly on iron (Fe) and aluminum (Al) hydroxides, resulting in low P fertilizer use efficiency. Organic chelating agents form strong bonds with metals in soil and may reduce P binding with Fe and Al and increase fertilizer P use efficiency. Ethylenediamine tetraacetic acid (EDTA), hydroxyethyl ethylenediamine triacetic acid (HEEDTA), gluconic acid, and citric acid were tested to determine their influence on water-soluble P (WSP), Mehlich-1 P, and Mehlich-3 P in a loam and sand fertilized with P and incubated for 49 days. Soil P sorption capacity (PSC) was estimated from an oxalate extraction of Fe and Al, and chelates were applied at rates of 90% of the PSC. EDTA and HEEDTA were also applied at 0, 30, 60, 90, 120, and 150% PSC to produce a rate response curve for WSP in a second soil incubation. The EDTA, HEEDTA, and citric acid significantly (P < 0.05) reduced P sorption in the loam and sand when measured by WSP. In soils without P fertilizer added, EDTA and HEEDTA resulted in a significant increase in WSP concentrations, as well as increased concentrations of Mehlich-1 P and Mehlich-3 P. With increasing chelation rates of EDTA and HEEDTA, there was a linear increase in WSP for both soils, indicating higher rates were most effective at decreasing P sorption. The application of chelating agents, with and without P fertilizer, could potentially increase plant availability of P, therefore reducing P fertilizer.

Detectability of15N-depleted fertilizer N in soil and plant tissue during a corn-rye crop rotation

Use of15N-depleted fertilizer materials have been primarily limited to fertilizer recovery studies of short duration. The objective of this study was to determine if15N-depleted fertilizer N could be satisfactorily used as a tracer of residual fertilizer N in plant tissue and various soil N fractions through a corn (Zea mays L.) -winter rye (Secale cereale L.) crop rotation. Nitrogen as15N-depleted (NH4)2SO4 was applied at five rates (0, 84, 168, 252, and 336 kg N ha−1) to corn. Immediately following corn harvest a winter rye cover crop treatment was initiated. Residual fertilizer N was easily detected in the soil NO3--N fraction following corn harvest (140-d after application). Low levels of exchangeable NH4+-N (<2.5 mg kg−1) did not permit accurate isotope-ratio analysis. Fertilizer-derived N recovered in the soil total N fraction following corn harvest was detectable in the 0 to 30-cm depth at each N rate and in the 30 to 60 and 60 to 90-cm depths at the 336 kg ha−1 N rate. Atom %15N concentrations in the nonexchangeable NH4+-N fraction did not differ from the control at each N rate. Nitrogen recovery by the winter rye cover crop reduced residual soil NO3--N levels below the 10 kg ha−1 level needed for accurate isotope-ratio analysis. Atom %15N concentrations in the soil total N fraction (approximately one yr after application) were indistinguishable from the control plots below the 168, 252, and 336 kg ha−1 N rate at the 0 to 30, 30 to 60, and 60 to 90-cm depths, respectively. Recovery of residual fertilizer N by the winter rye cover crop was verified by measuring significant decreases in atom %15N concentrations in rye tissue with increasing N rates. The greatest limitation to the use of15N-depleted fertilizer N as a tracer of residual fertilizer N in a corn-rye crop rotation appears to be its detectibility from native soil N in the total N pool.

Reducing Corn Yield Variability and Enhancing Yield Through the Use of Corn-Specific Growth Models

Crop simulation models (CSMs) can evaluate the effects of management and environmental scenarios on crop growth and yields. Two corn (Zea mays L.) crop growth simulation models, Hybrid-Maize, and CERES-Maize, were calibrated and validated under mid-Atlantic United States conditions to provide better understanding of corn response to variable environmental conditions and developing management that decreases temporal yield variation. Calibration data were from small-plot population by maturity studies conducted across five site years. Model validation was performed on data from large, replicated trials from across Virginia. Both CSMs under-predicted corn grain yield. CERES-Maize grain yield prediction error was consistent across the range of plant density, whereas accuracy of Hybrid-Maize varied with density. Validation results of the calibrated CSMs showed reasonable accuracy in simulating planting date and environment on a range of corn hybrids. Because each model has unique strengths and assessment modules, the CSM can be matched to the individual use.

Phosphorus application to newly‐cleared coastal plain soils: Corn (Zea mays L.) response and soil test calibration data

Abstract Phosphorus applications ranging from 0 to 288 kg P/ha were broadcast alone and in combination with band treatments of 22 kg P/ha to two newlycleared Kempsville sandy loam (Typic Hapludults) soils for the purpose of measuring corn (Zea mays L.) yield responses and obtaining soil test calibration data. Four to 10‐fold corn grain yield increases resulted from P additions. Broadcast applications of 96 kg P/ha in combination with band treatments of 22 kg P/ha from either diammonium phosphate or ammonium polyphosphate were most efficient in increasing corn grain yields to 80% or more of maximum yield. Critical extractable soil P values for the two sites of 31 and 42, 29 and 37, 18 and 19, and 47 and 43 ppm were obtained for the Bray I, North Carolina (NC), Olsen, and Mehlich III soil test procedures, respectively. Increases in extractable soil P with increasing P applications expressed as ppm P/kg P applied varied for the two sites from 0.21 to 0.26 for the Bray I and NC procedures, 0.10 to 0.13 for th...

Plant-Available Phosphorus after Application of Synthetic Chelating Agents

ABSTRACT Fertilizer phosphorus (P) can become immobilized in acidic soils through bonds with iron (Fe) and aluminum (Al). Two chelating agents, ethylenediamine tetraacetic acid disodium salt (EDTA) and hydroxyethyl ethylenediamine triacetic acid (HEEDTA), were tested in a greenhouse study for efficiency at increasing plant-available P to corn (Zea mays L.). Fertilizer P was added with or without chelate to the center of pots, simulating a starter band of P. Without the presence of chelates, biomass above and below ground increased linearly as P fertilizer rates increased at 0, 9.6, 19.3, 28.9, and 38.5 kg P ha−1. Applications of EDTA and HEEDTA did not significantly increase water-soluble P (WSP), Mehlich 1 P, and Mehlich 3 P compared to soils without chelates. Applications of EDTA increased P uptake in the belowground biomass. Despite previous research showing that chelates increased WSP in soils, a decrease in P sorption was not observed with the additions of chelating agents to soils.

Ureolytic Activity of Soybean and Corn Residue Extracts

The enzyme urease is responsible for the rapid hydrolysis of urea in agroecosystems where more than 50% of the applied nitrogen (N) can be lost via ammonia volatilization. The objectives of the study were to (1) extract urease from corn (Zea mays L.) and soybean (Glycine max L.) and (2) compare the urease activity from soybean and corn residues to Jackbean (Canavalia ensiformis) urease using Fourier transform infrared spectroscopy (FTI-R). Concentrations of urea and sodium bicarbonate ranging from 0 to 200 mM were analyzed with FTI-R to determine the correlation to peak height. Bicarbonate produced the most responsive peaks to concentration at 1,362 cm−1. Urease extracted from soybean residue was active, producing a bicarbonate peak at 1362 cm−1, whereas no urease activity was observed in corn residue. Variation among urease activities in crop residues could suggest a need for more precise nitrogen management in conservation tillage agroecosystems to reduce ammonia volatilization.