Irrigated Corn Yields Research Articles

Economic Profitability of Sustained Application of Swine Lagoon Effluent and Beef Feedlot Manure Relative to Anhydrous Ammonia in the Oklahoma Panhandle

With the rapid growth of swine (Sus scrofa domestica) production in the Oklahoma Panhandle, animal waste management has become a growing concern. Field experiments were conducted to evaluate the long‐term effects of equivalent nitrogen rates of swine lagoon effluent (SE), beef manure (BM), and commercial fertilizer on the yield and economic returns of irrigated corn (Zea mays L.) grown on calcareous Gruver silt loam soil (fine, mixed, superactive, mesic Aridic Paleustoll) near Goodwell, Oklahoma. A randomized, complete‐block, split‐plot design with three replications was used to test the main effects of N source (NS) and equivalent N application rates (NR) of 56, 168, and 504 kg N ha−1 Both BM and SE generated significantly (P < 0.05) higher corn yields than anhydrous ammonia (AA) across the main effect of NS. Greater separation of mean corn yields was found among NS as the equivalent NR rate was increased from 56 to 504 kg N ha−1 with the following rankings (P < 0.05): AA = BM = SE at 56 kg N ha−1, BM = AA ≥ SE at 168 kg N ha−1, and SE > BM > AA at 504 kg N ha−1 Both SE and BM generated significantly (P < 0.05) higher economic returns than AA. The highest ranked alternatives of economic returns were generated by SE×504 and BM×168. Results indicate that SE and BM can be economically viable substitutes for commercial fertilizer, bringing higher yields and economic benefits to producers in the Oklahoma Panhandle.

Compactação do solo e produção de cultivares de milho em latossolo vermelho: II - intervalo hídrico ótimo e sistema radicular

Este trabalho teve como objetivo avaliar, no campo, a resposta de duas cultivares de milho em um Latossolo Vermelho, em seis níveis de compactação, quanto ao desenvolvimento do sistema radicular, bem como caracterizar a compactação do solo a partir do intervalo hídrico ótimo (IHO). O experimento foi realizado em faixas, no delineamento de blocos completos casualizados, com quatro repetições. Utilizaram-se os híbridos de milho DKB 390 e DAS 2B710. Após a semeadura do milho, coletaram-se amostras indeformadas de solo para a determinação de propriedades físicas do solo e do IHO. No estádio do pendoamento do milho, retiraram-se três amostras por parcela na entrelinha, nas profundidades de 0-10, 10-20 e 20-30 cm, em cada parcela, para determinação de diâmetro médio, densidade do comprimento radicular e massa de matéria seca das raízes. O IHO foi igual a zero quando o solo atingiu a densidade crítica de 1,46 kg dm-3, correspondente a 92 % da densidade máxima do solo. Com a compactação, houve aumento da produção de matéria seca das raízes, da densidade do comprimento radicular e do diâmetro radicular e na profundidade de 0-10 cm, o aumento da massa de matéria seca e da densidade radicular se dá até a resistência do solo à penetração de 1,23 e 1,43 MPa, respectivamente. Houve correlação negativa entre a massa de matéria seca, a densidade e o diâmetro radicular com a produtividade do milho irrigado, mostrando que essas variáveis são bons indicadores da compactação do solo.

Corn Response to Nitrogen Rate, Row Spacing, and Plant Density in Eastern Nebraska

Efficient use of N by corn (Zea mays L.) is financially and environmentally important, and may be improved with higher plant density and reduced row spacing. Hypotheses were tested that irrigated corn yield in northeast Nebraska is increased by reducing row spacing from 0.76 m and increasing plant density above 61 800 plants ha−1, and that grain yield response to applied N is greater with reduced row spacing and increased plant density. Field experiments were conducted for 3 yr comparing the effects 0.76‐ vs. 0.51‐m row spacing, three plant densities, and four N rates on crop performance. The soil was a silty clay loam (mesic Cumulic Haplustoll). Nitrogen rates ranged from 0 to 252 kg N ha−1. Plant N concentration and biomass and grain yield were not affected by plant density. Decreasing row spacing from 0.76 to 0.51 m resulted in 4% more grain yield. Grain yield response to applied N and N rates for optimum yield were not affected by row spacing. Nitrogen application resulted in mean increases of 22% more biomass production and 24% more grain yield. The N response function was linear in 1996, quadratic in 1997, and quadratic with decreased yields at the high N rate (252 kg N ha−1) in 1998. Grain yield was not affected by increasing plant density above 61 800 plants ha−1 but was greater with narrow row spacing. Yield response to applied N was similar for all planting arrangements. Optimal N rate cannot be better predicted by considering plant density and row spacing.

Spatial Variability of Irrigated Corn Yield in Relation to Field Topography and Soil Chemical Characteristics

Corn yield, topography and soil characteristics were sampled on a 26 ha area of a centre pivot irrigated cropland. The aim of the study was to determine relationships between corn yield, field topography and soil characteristics. The study was carried out in the Alentejo region of Portugal. Corn yield was measured with a combine harvester fitted with a grain-flow sensor and positioned by means of the Global Positioning System (GPS). A grid-based digital elevation model (DEM) with 1-m resolution was constructed and several topographic attributes were calculated from the DEM: the local slope gradient (S), profile curvature (Curv), specific catchments area (SCa), and a steady-state wetness index (W). Yield and topographical attributes were computed for areas of radius 5, 10, 25 and 50 m, being considered its maximum, minimum, range and average values. The soil was systematically sampled with a mechanical probe for a total of 109 soil profiles used for analysis of the following soil superficial (<0.30 m) characteristics: extractable phosphorous (P2O5) and extractable potassium (K2O), soil pH, cation exchange capacity (CEC) and exchangeable bases. With centre pivot irrigation systems, the Wave50 index was shown to be useful for the identification of field areas in which low corn yields may be due to lack of water. At the same time, SCa was found to be useful for the identification of field areas in which low yields are due to excess water and drainage problems. Higher positive correlation between pH, Ca and Curv were observed; calcium concentration was found on the transition areas between flat surfaces to concave ones, while lower values were detected in convex and concave areas. Topographical indexes, namely Wave50, SCa and Curv, can be especially helpful in site-specific management for delineating areas where crop yields are more sensitive to extreme water conditions.

Appropriateness of Management Zones for Characterizing Spatial Variability of Soil Properties and Irrigated Corn Yields across Years

Recent precision-agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZ that characterize spatial variation in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field. A georeferenced soil-sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997–2001) seasons. The five landscape attributes were aggregated into four MZ using principal-component analysis of landscape attributes and unsupervised classification of principal-component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest- and lowest-yielding MZ in three of five seasons, receiving average precipitation, less-pronounced (≤5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions.

Appropriateness of Management Zones for Characterizing Spatial Variability of Soil Properties and Irrigated Corn Yields across Years

Recent precision‐agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZ that characterize spatial variation in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field. A georeferenced soil‐sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997–2001) seasons. The five landscape attributes were aggregated into four MZ using principal‐component analysis of landscape attributes and unsupervised classification of principal‐component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest‐ and lowest‐yielding MZ in three of five seasons, receiving average precipitation, less‐pronounced (≤5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions.

Evapotranspiration, yield and water use efficiency of drip irrigated corn in the Bekaa Valley of Lebanon

We measured and compared evapotranspiration (ET) of a corn hybrid in 1998 and 1999 under full and deficit irrigation at Tal Amara Research Station in the Bekaa Valley of Lebanon, and studied differences in growth, yield and water use efficiency (WUE). In both years, corn was planted in May and harvested in September in two different fields of 2200 m2 each, containing drainage lysimeters to directly measure ET. Irrigation differentiation was made upon crop evapotranspiration measured on the lysimeters, water was then applied at 100 and 60% of ET. Full irrigation treatment (I-100) was managed for high productivity, whereas deficit irrigation treatment (I-60) was maintained at 60% of field capacity. Water stress was applied continuously during the growing cycle. Seasonal ET reached on the lysimeter amounts of 952 and 920 mm in 1998 and 1999, for total growing cycles of 128 and 120 days from sowing till harvest. Peak daily ET rates exceed at anthesis the evaporation of pan class A (some >14 mm per day) and were not appreciably year-different when fully irrigated although seasonal ET was less in 1999. Leaf area index and dry matter decreased in the I-60 treatment. Leaf area index (LAI) was slightly higher than 7.0 in 1998 and nearly 6.0 in 1999 in the I-100 treatment. However, LAI decreased in both years by more than 25% in the I-60 treatment. Grain yield on a dry basis declined in 1998 from 1520 g m-2 on the lysimeter to 1450 g m-2 on the full irrigated treatment to 1080 g m-2 on the water deficit treatment. In 1999, these reductions ranged from 1340 g m-2 on the lysimeter to 1280 and 1040 g m-2 on I-100 and I-60, respectively. Total aboveground dry mater was also reduced by water stress. In 1998, a reduction of 130 g m-2 was observed at harvest in I-100 in comparison with the lysimeter, while the reduction on I-60 exceeded 800 g m-2 when compared to I-100. In 1999, these reductions were 100 and 400 g m-2, respectively. Grain-related water use efficiency (WUEg) of lysimeter grown plants was 1.52 kg m-3 in 1998 and 1.34 kg m-3 in 1999. However, fully irrigated corn had a WUEg of 1.68 kg m-3 in 1998 and 1.54 kg m-3 in 1999. Higher WUEg values of 1.88 kg m-3 and 1.87 kg m-3 were obtained in 1998 and 1999, respectively, from the I-60 treatment. On a biomass basis, I-100 treatment had values of water use efficiency (WUEb) of 3.16 and 2.46 kg m-3 in 1998 and 1999, respectively, while the I-60 treatment had values of 3.23 and 2.97 kg m-3, respectively. On the lysimeter, these values were 3.0 and 2.34 kg m-3, respectively. Finally, results revealed that cultivar Manuel maintained high levels of dry matter partitioning to reproduction organs under the high temperature/low humidity conditions of the Bekaa Valley, which makes it suitable for semi-arid environments. Author Keywords: Zea mays L.; Water stress; Deficit irrigation; Evapotranspiration; Water use efficiency

Quantifying effects of soil conditions on plant growth and crop production

Soil management decisions often are aimed at improving or maintaining the soil in a productive condition. Several indicators have been used to denote changes in the soil by various management practices, but changes in bulk density is the most commonly reported factor. Bulk density, in and of itself, gives little insight on the underlying soil environment that affects plant growth. We investigated using the Least Limiting Water Range (LLWR) to evaluate changes in the soil caused by soil management. The LLWR combines limitations to root growth caused by water holding capacity, soil strength and soil aeration into a single number that can be used to determine soil physical improvement or degradation. The LLWR appeared to be a good indicator of plant productivity when the full potential of water holding capacity on available water can be realized, such as with wheat (Triticum aestivum, L.) grown in a no-till system when the wheat followed a fallow period. A regression of wheat yield to LLWR gave an r 2 of 0.76. The LLWR was a poorer indicator of plant productivity when conditions such as low total water availability limited the expression of the potential soil status on crop production. Dryland corn (Zea mays, L.) yields were more poorly correlated with LLWR (r 2 =0.18), indicating that, under dryland conditions, in-season factors relating to water infiltration may be more important to corn production than water holding capacity. An improved method to evaluate in-season soil environmental dynamics was made by using Water Stress Day (WSD). The WSD was calculated by summing the differences of actual water contents in the field from the limits identified by the LLWR during the growing season. A regression of irrigated corn yield with LLWR as the soil indicator of the soil environment resulted in an r 2 of 0.002. A regression of the same yield data with WSD as the indicator of the soil environment resulted in an r 2 of 0.60. We concluded that the LLWR can be a useful measure of management effects on soil potential productivity. Soil management practices that maximize the LLWR can maximize the potential of a soil for crop production. Knowledge of the LLWR for a soil can help the farm manager optimize growing conditions by helping schedule irrigation and for making tillage decisions. The WSD, calculated from the LLWR and in-season water dynamics, allows us to evaluate changes in the

Impact of Palmer Amaranth (Amaranthus palmeri) on Corn (Zea mays) Grain Yield and Yield and Quality of Forage1

Studies were conducted at one location in 1997 (W97) and in two locations in 1998 (E98 and W98) near Garden City, KS, to evaluate the impact of Palmer amaranth at densities of 0, 0.5, 1, 2, 4, and 8 plants/m of row on forage yield and quality of irrigated corn and to determine if harvesting Palmer amaranth–infested corn for forage rather than for grain would reduce losses. Weed-free corn, Palmer amaranth alone, and corn–Palmer amaranth harvested together were evaluated for forage yield and quality. Forage quality was determined by evaluating in vitro dry matter digestibility (IVDMD), acid detergent fiber (ADF), neutral detergent fiber (NDF), and crude protein (CP). Corn grain and forage yield declined with increasing Palmer amaranth density. However, decline in forage yield ranged from 1 to 44% of the weed-free yield at Palmer amaranth densities of 0.5 and 8 plants/m of row, whereas decline in grain yield ranged from 11 to 74% of the weed-free yield at the same densities. Digestibility of weed-free corn forage, expressed as IVDMD, was significantly higher than that of Palmer amaranth alone at W97 and W98. The CP of weed-free corn forage was similar to that of Palmer amaranth forage at W98, but it was lower at the other two locations. In contrast, CP did not differ between corn–Palmer amaranth harvested together and weed-free corn. The IVDMD of weed-free corn forage was greater than that of corn–Palmer amaranth mixture at W98, but no differences were observed at the other two locations. The relative feeding values of weed-free corn and corn–Palmer amaranth mixture were similar, and greater than that of Palmer amaranth in monoculture. These results indicate that Palmer amaranth interference in corn may not affect forage quality but can cause a decline in yield. This decline in yield is less when harvesting corn and Palmer amaranth together for forage rather than for harvesting corn grain alone.Nomenclature: Palmer amaranth, Amaranthus palmeri S. Wats. #3 AMAPA; corn, Zea mays L.Additional index words: Forage quality, weed density, yield loss.Abbreviations: ADF, acid detergent fiber; CP, crude protein; DM, dry matter; IVDMD, in vitro dry matter digestibility; NDF, neutral detergent fiber; RFV, relative feed value.

Interference of Palmer amaranth in corn

Abstract Palmer amaranth (Amaranthus palmeri) is a major weed in corn (Zea mays) fields in the southern Great Plains of the United States. Field studies were conducted in 1996, 1997, and 1998 near Garden City, KS, to evaluate the effects of Palmer amaranth density and time of emergence on grain yield of irrigated corn and on seed production of Palmer amaranth. Palmer amaranth was established at densities of 0.5, 1, 2, 4, and 8 plants m−1 of corn row both concurrently at corn planting and when corn was at the three- to six-leaf stage. The control plots were weed free. The Palmer amaranth planted with corn emerged with corn, whereas that planted later emerged at the four-, six-, and seven-leaf stages of corn. The Palmer amaranth emerging with corn reduced yield from 11 to 91% as density increased from 0.5 to 8 plants m−1 of row. In contrast, yield loss from Palmer amaranth emerging later than corn was observed only when the emergence occurred at the four- and six-leaf stages. The corn leaf area index (LAI) ...

Irrigated Corn Yield and Nitrogen Accumulation Response in a Comparison of No‐till and Conventional Till: Tillage and Surface‐Residue Variables

AbstractComparisons between no‐till and conventional‐till management are often confounded by variation in both tillage and residue placement. The objective of this research was to separate the tillage variable from the surface‐residue variable associated with no‐till and conventional‐till management comparisons in irrigated continuous corn (Zea mays L.) production. Two Nebraska locations (Mead and Clay Center) with differences in soil types and climate were selected. Four tillage‐residue treatments [NT‐NR (no‐till, residue removed), NT‐R (no‐till, surface residue), T‐NR (till, residue removed), T‐R (conventional till, surface residue)] were fertilized by either broadcasting at planting or sidedressing at the 6‐leaf stage with rates of 0, 56, 112, and 168 kg N ha−1. At Clay Center, grain yields and total N accumulation were similar for all tillage‐residue treatment combinations in all years when the highest fertilizer N rate was used. In 2 of 3 yr at Mead, grain yields and total N accumulation were less for no‐till than conventionaltill treatments, but in 1 yr the yields and total N accumulations were greater in no‐till than conventional‐till treatments. At Mead, surface residue resulted in lower grain yields and total N accumulation compared with bare soil at lower N rates, but not at greater N rates, in 2 of 3 yr. Sidedressing fertilizer N was generally a more efficient N placement than broadcasting. Differences between tillage and residue effects at Clay Center and residue effects at Mead were overcome with higher rates of fertilizer N. Tillage effects at Mead did not appear to be N‐related. The data suggest that tillage may be necessary to maintain optimum production levels on finer‐textured soils when spring soil temperatures are cool and slow to warm. When spring soil temperatures are warm, no‐till strategies can be used for optimum production levels on these soils.

Yield and Nitrogen Use Efficiency of Irrigated Corn in the Northern Great Plains

AbstractNitrogen and water are the two most common limitations to crop production in the semiarid northern Great Plains. Little is known about N use efficiency by irrigated corn (Zea mays L.) in this region. A study was conducted to determine how irrigation and N fertility levels affect growth and N use efficiency by corn. Corn was grown under three irrigation levels: precipitation plus irrigation equal to one, two, and three times the calculated evapotranspiration (ET) rate. Fertilizer use efficiency was determined using 15N‐enriched fertilizer applied at rates equivalent to 100 and 200 kg N ha−1. Grain and dry matter yields, N content, and utilization of fertilizer N all exhibited yearly variations, probably the result of annual weather patterns, especially temperature. For years when temperatures during the growing season were below the 30‐yr average and affected corn growth, there were no differences in yields and N content between the two fertility levels. For years when temperatures during the growing season were warm enough for favorable growth, corn responded to increasing N fertility with 60% greater yields, 75% greater N content, and 60% greater percentage N derived from fertilizer with the higher N fertility treatment. Averaged across rates, grain utilized 35% and stover an additional 15% of the applied fertilizer, while 30% remained in the upper 0.6 m of the soil profile at the end of the growing season. Twenty percent of the applied fertilizer could not be accounted for, lost to leaching or denitrification. Supplemental irrigation and N fertilization are viable management practices available to producers in the semiarid northern Great Plains.

Influence of Weed Density and Distribution on Corn (Zea mays) Yield

The impact of weed density and weed distribution on irrigated corn yield was investigated in Colorado. Weed densities examined were 0,33,50, or 100% of the indigenous weed population. A series of weed distribution treatments were achieved by varying the length of the weed-free and weedy zones within the corn row while maintaining a constant weed population of 33 or 50% of the indigenous weed level. Grain yield was affected by weed density, but not by weed distribution. Each additional weed reduced corn yield 8.5 and 2.3 kg ha−1in 1991 and 1992, respectively. When corn yields were estimated with a computer weed/corn management model, weed densities 5 to 8 wk after planting provided a better yield reduction estimate than weed densities immediately before harvest.

Corn (Zea mays) Response to Post-directed Sethoxydim Under Irrigated and Dryland Conditions

Four corn hybrids were evaluated for tolerance to sethoxydim at 110 and 220 kg ha–1applied post-directed at two growth stages (V6–7 and V10–11). Dryland corn grain yields did not respond to sethoxydim, while irrigated corn yields were sensitive to sethoxydim treatments. Sethoxydim at 220 g ha–1reduced the grain yield of hybrid 3377 by 12% at both growth stages. Sethoxydim at the same rate reduced grain yield of hybrid 3379 by 15% when applied to V6–7 corn. Hybrid 3475 had an 11% grain yield reduction from sethoxydim applied at either dosage to V10–11 corn. Under irrigated conditions, a trend toward reduced grain yield was observed for hybrid 3183 at all application times and sethoxydim rates. Corn ear weights and kernel weights differed among hybrids but did not exhibit a response to sethoxydim within hybrids. Visual evaluation for crop injury and measured corn heights did not indicate a response to sethoxydim. There was no yield response in any hybrid to 110 g ha–1applied to V6–7 stage corn indicating this treatment was safe to use on all hybrids evaluated.

The Effect of Rye Cover Crop and Nitrogen Fertilizer Rate on Yield of Irrigated Corn and Residual Soil Nitrogen

The Effect of Rye Cover Crop and Nitrogen Fertilizer Rate on Yield of Irrigated Corn and Residual Soil Nitrogen

Effect of evapotranspiration underprediction on irrigation scheduling and yield of corn: a simulation study

Abstract Underprediction of evapotranspiration ( et ) introduces inaccuracies in water balance-based irrigation scheduling procedures. This may reduce crop yield. A simulation study was performed to evaluate sprinkler irrigated corn yield as affected by irrigation schedules resulting from three levels of et underprediction. Four irrigation uniformity treatments, two soil types, and two weather scenarios in central Washington were also considered. Yield reductions ranging from 1 to 7% and from 8 to 27% were predicted when daily et was underpredicted by 15% and 30%, respectively. Implications of underpredicting et in water balance-based irrigation scheduling techniques are discussed.

The impact of climate change on continuous corn production in the Southern U.S.A.

The Goddard Institute for Space Studies (GISS) General Circulation Model (GCM) has been used in conjunction with a field level plant process model (CERES-Maize) and a field level pesticide transport model (PRZM) to study the impacts of doubled levels of atmospheric CO2 on various aspects of corn production in the Southern U.S.A. Grid-box scale GCM output has been applied to a 38-year time series of historical weather data at 28 different locations for several typical soil profiles throughout the South. Limitations on the use of the climate scenario in conjunction with the process models are discussed. Major shortcomings include: 1) no direct impacts of atmospheric CO2 on plant growth and development in the plant process model; 2) neither macro-pore solute transport nor chemical decay rate response to temperature are included in the pesticide transport model; and 3) the climate change scenario output does not provide information concerning changes in temperature extremes and variability or precipitation frequency, intensity or duration. The latter are particularly critical parameters for the detailed simulation of hydrological processes. In spite of these omissions, the combination of the three models facilitates the study of the impacts of GCM modeled climate change on several inter-related agro-climatic issues of interest to agricultural policy makers. These issues include: changes in dryland and irrigated corn yields; changes in sowing and harvest dates; modification of crop water demand; and estimates of effects on pesticide losses from the soil surface and through leaching from the bottom of the active corn root zone. Model generated results which address these issues are presented but must be used with caution in light of the GCM and process model limitations. The results of this study suggest that substantial changes in agricultural production and management practices may be needed to respond to the climate changes expected to take place throughout the Southern U.S.A.

Nitrogen Management and Nitrification Inhibitor Effects on Nitrogen‐15 Urea: I. Yield and Fertilizer Use Efficiency

AbstractNitrification inhibitors (NI) are sometimes recommended for use with ammoniacal fertilizers in corn (Zea mays L.) production to improve fertilizer N use efficiency (FUE). The objectives of this experiment were to evaluate the effects of the NI nitrapyrin [2‐chloro‐6‐(trichloromethyl) pyridine] application on yield and FUE of irrigated corn, and to monitor the fate of a single application of 15N‐enriched urea during a multiyear period in both soil and plant. Treatments included a factorial combination of two N rates (90 or 180 kg urea‐N ha−1 yr−1) applied during a 3‐yr period, with or without a NI and with or without incorporation, plus a zero‐N control. Twenty‐seven nonweighing lysimeters were used to quantify leaching load. Treatment effects on yield and FUE differed each year due to interactions of climate and N‐management variables. Nonincorporated urea + NI reduced grain yield when leaching load was low and increased yield at the 90 kg ha−1 N rate when leaching load was high. Maximum FUE occurred at the 90 kg ha−1 N rate when leaching load was low. The NI increased FUE only at the 90 kg ha−1 N rate when leaching load was high. Incorporation of urea + NI reduced plant recovery of fertilizer‐derived N (FDN) in the year of application, but resulted in increased uptake of residual FDN in subsequent years. Incorporation of NI with moderate N rates coupled with conservative irrigation management should reduce the risk of yield loss and minimize NO3 movement to groundwater.

Irrigated Corn Response to Soil‐Test Indices and Fertilizer Nitrogen, Phosphorous, Potassium, and Magnesium

AbstractImproved soil‐water management techniques have made irrigated corn (Zea mays L.) yields of more than 12.5 Mg ha−1 possible in the southeastern USA. Data relating fertilizer rates and soil test indices to grain yield under intensive water management are needed to maximize fertilizer use efficiency. The objective of this study was to generate fertility index‐yield response data from which critical levels of Mehlich 1 soil test P, K, and Mg could be calculated. Irrigated corn was grown at Quincy, FL during 1980 and 1981. Nitrogen was applied at 168, 336, and 504 kg ha−1, P at 0, 29, 59, and 118 kg ha−1, K at 0, 209, and 418 kg ha−1, and Mg at 0, 67, and 134 kg ha−1 in a total of 11 treatments. Indices of available nutrients were measured via the Mehlich 1 soil test prior to each season. For both years, a minimum application of 168 kg ha−1 of N, 29 kg ha−1 of P, and 0 kg ha−1 of Mg was required for maximum grain yield, which averaged 11.2 Mg ha−1. For K, maximum yield occurred with minimum applications of 209 and 0 kg ha−1 in 1980 and 1981, respectively. Calculated critical Mehlich 1 soil test levels were 9, 45, and 33 mg kg−1 for P, K, and Mg, respectively. Comparison of our results with current soil test rating categories and corresponding recommended fertilizer rates indicated that maximum corn yield was obtained with a P fertilizer rate which was 50 kg ha−1 lower than the recommended rate.

Fertilizer Nitrogen and Residual Nitrate‐Nitrogen Effects on Irrigated Corn Yield

AbstractMultirate nitrogen studies were conducted for a 6‐yr period, on an irrigated clay loam soil, to determine the influence of applied N and residual soil N on the grain yield of corn (Zea mays L.). Soil samples were taken prior to fertilizer application each year in depth increments of 0 to 0.15, 0.15 to 0.30, 0.30 to 0.60 and 0.60 to 0.90 m and analyzed for nitrate‐N (NO‐3‐N). Applied N and residual soil NO‐3‐N were found to significantly influence grain yields. Regression analyses of the data showed highly significant relationships between (i) quantities of NO‐3‐N measured in the upper portions and those measured in the lower portions of the soil profile and (ii) grain yield and applied N and residual NO‐3‐N. Highest coefficients of determination were obtained when residual NO‐3‐N was included as a separate independent variable in the regression equation. Results indicated that residual NO‐3‐N measured to 0.15 m would be sufficient for evaluation of residual N effects on irrigated corn grain yield on this soil. Fertilizer N requirements for several combinations of grain yield and residual soil NO‐3‐N were calculated using the N requirement index (NRI) and a power function, and simple and multiple linear response equations generated by regression analysis. A range of values was obtained, with NRI most frequently predicting the highest N requirement. The marginal rate of substitution of residual soil NO‐3‐N for applied fertilizer N was variable and influenced by (i) amount of residual NO‐3‐N, (ii) depth of measurement of residual NO‐3‐N and (iii) maximum grain yield. Fertilizer use efficiency (FUE) was influenced by grain yield, fertilizer N rate, and amount of residual soil NO‐3‐N. The greatest reduction in FUE resulted from residual soil NO‐3‐N. In order to maximize FUE, it is necessary to apply the amount of fertilizer N to achieve a given yield level and simultaneously leave as little as possible in the soil to carry over to the next crop year.