Irrigated Corn Research Articles

The Effects of Microdrip and Conventional Drip Irrigation on Water Distribution and Uptake

Drip irrigation at a rate close to plant water uptake necessitates low application rates (microdrip), which affect soil water regime and plant response. This study compare the effect of three emitter discharges, 0.25, 2.0, and 8.0 L h−1, on different aspects of the water regime in daily drip irrigated corn (Zea Mays L.), relying on field observations and numerical simulations. Field observations show that microdrip irrigation (i) tends to increase yield although this was not statistically significant under the experimental conditions; (ii) induces higher relative water content values in the 0‐ to 0.30‐m depth layer, and lower ones in the 0.60‐ to 0.90‐m layer. Numerical simulations, carried out using HYDRUS‐2D, show that microdrip irrigation led to the smallest wetted volume with the least extreme water content gradients both in the horizontal and the vertical axes. A saturated zone below the emitter was obtained only for the 8.0 L h−1 discharge. Comparing water content distributions with depth at the end of the application of the same amount of water close to the emitter, the driest profile is obtained for the lowest application rate. However, when compared at solar noon representing the time of the highest plant water demand, the upper 0.20‐m layer of the soil irrigated at the lowest rate was the wettest. Microdrip irrigation has reduced the dynamic changes in the water content during the day in the most active part of the root zone. It also caused the smallest reduction in the simulated water uptake relative to the potential value.

Modeling the Development of Resistance by Stalk-Boring Lepidoptera (Crambidae) in Areas with Irrigated Transgenic Corn

The population dynamics and population genetics of two bivoltine species of corn borers are modeled in a hypothetical region of irrigated transgenic and nontransgenic corn. European corn borer, Ostrinia nubilalis (Hübner), adults were assumed to disperse throughout the landscape for both mating and oviposition. Southwestern corn borer, Diatraea grandiosella Dyar, adults were assumed to have very localized dispersal behaviors. Resistance developed quickly in both species when the allele for resistance to the transgenic toxin was dominant. When the allele for resistance was not dominant and few or none of the heterozygous larvae survived the toxin, the behaviors of adult insects determined the speed of resistance development. With block refuges of 10–40% the European corn borer developed resistance within 15–38 yr, but the southwestern corn borer never developed resistance within the 100 yr simulated. A row-strip refuge configuration did not change the time for resistance to develop in the European corn borer; however, row-strip refuges cannot be recommended for the southwestern corn borer. Uncertainty about adult behaviors in irrigated corn led us to examine the potential impact of behavior on resistance development. Adult behaviors influenced resistance development more than refuge size. For instance, if the first flight of moths exhibit random mating and uniform oviposition throughout the landscape and the second flight exhibits localized mating and oviposition, resistance developed at least five times faster in the southwestern corn borer population and three times slower in the European corn borer population compared with our standard assumptions. We discuss the implications of adult behavior, refuge configuration, refuge placement within the landscape and year-to-year relocation on resistance management plans.

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.

Nitrate contamination of a rural aquifer and accumulation in the unsaturated zone

Groundwater contamination was studied in a rural setting of the Upper Pantanoso Stream Basin (UPSB) in the southeast of Buenos Aires Province, Argentina, where potential contaminant sources include inorganic fertilizer. Nitrate–N concentrations, greater than accepted level for safe drinking-water of 10 mg l −1 were present in 36% of sampled wells and 67% of samples had nitrate concentrations exceeding the background level of 5 mg l −1. Temporal fluctuation of nitrate concentrations in the groundwater was attributed to seasonal fluctuations in recharge and plant growth. Nitrate concentration was measured in deep soil profiles to determine the extent of leaching. Nitrate accumulation in the unsaturated zone of a soil cropped with potatoes was three times higher than the baseline N concentration found in the pasture. The greatest nitrate concentration in the soil profile occurred under irrigated corn where excessive nitrogen was applied. These results show that high fertilization rates and irrigation lead to increased hazards of groundwater pollution.

Infestation and spatial dependence of weed seedling and mature weed populations in corn

Abstract Knowing the distribution of weed seedlings in farmer-managed fields could help researchers develop reliable distribution maps for site-specific weed management. With a knowledge of the spatial arrangement of a weed population, cost effective sampling programs and management strategies can be designed, so inputs can be selected and applied to specific field areas where management is warranted. In 1997 and 1998, weeds were sampled at 612 to 682 sites in two center pivot irrigated corn fields (71 and 53 ha) in eastern Colorado. Weeds were enumerated when corn reached the two-leaf, four-leaf, and physiological maturity stages in a 76.2- by 76.2-m grid, a random-directed grid where sites were established at intervals of 76.2 m, and a star configuration based on a 7.62- by 7.62-m grid within three 23,225 m2 areas. Directional correlograms were calculated for 0, 30, 60, 90, 120, and 150° from the crop row. Fifteen weed species were observed across fields. Spatial dependence occurred in 7 of the 93 sampl...

Delayed control of a hairy vetch ( Vicia villosa Roth) cover crop in irrigated corn production

Although a hairy vetch ( Vicia villosa Roth) cover crop can supply nitrogen and suppress weeds, corn planting in central Illinois must be delayed past optimum planting dates to realize significant benefits from this cover crop. As an alternative to delayed planting, controlling a band of hairy vetch over corn rows followed by a sequential treatment between the rows may allow for increased vegetative growth and greater weed suppression. Vetch between the rows provided greater than 80% weed control if allowed to grow for at least four weeks. These treatments, however, reduced corn height by approximately 20%. If hairy vetch between the rows was controlled within 2 weeks of planting, it did not appear to adversely affect crop growth.

Dispersal of adult European corn borer (Lepidoptera: Crambidae) within and proximal to irrigated and non-irrigated corn.

The European corn borer, Ostrinia nubilalis (Hübner), causes economic damage to corn, Zea mays L., throughout the Corn Belt. Because this insect has become the primary target of Bacillus thuringiensis Berliner (Bt) transgenic corn, current efforts addressing the management of O. nubilalis resistance to Bt corn require information on adult European corn borer dispersal and factors affecting its dispersal. In 1998 we conducted mark-release-recapture, release-recapture, and caged-mating studies to directly measure and compare local dispersal patterns of O. nubilalis adults within and proximal to irrigated and non-irrigated cornfields. Releases of marked adults were made corresponding to the first and second flight of O. nubilalis in eastern Nebraska. Adult dispersal was significantly different between irrigated and non-irrigated cornfields. Released adults tended to remain in and near irrigated cornfields, but dispersed out of and away from non-irrigated cornfields. When released at the edge of the cornfield, neither male nor unmated female O. nubilalis displayed an initial tendency to move out of irrigated corn and into the mixed smooth bromegrass (Bromus inermis Leyss) and broadleaf-weed field edge. Mating efficiency in a late-season cornfield was not significantly different than in dense foxtail (Setaria spp.). Generally, we found that adult O. nubilalis dispersal may vary depending on variables such as action-site availability and agronomic practices and their interaction with O. nubilalis life history.

Economic Analysis of Conservation and Conventional Tillage Cropping Systems on Clayey Soil in Eastern Arkansas

Conservation tillage offers an alternative approach for managing clayey soils in the midsouthern United States. This study compared conservation tillage seedbed preparation vs. conventional tillage main plots with subplots of (i) nonirrigated soybean (Glycine max L. Merr.), (ii) irrigated soybean, (iii) irrigated grain sorghum (Sorghum vulgare L.), (iv) irrigated soybean followed by irrigated grain sorghum, (v) irrigated soybean followed by irrigated corn (Zea mays L.), and (vi) continuous irrigated cotton (Gossypium hirsutum L.) for the years 1986 to 1991 at Keiser, AR. Cropping practices were similar to those used by producers in the area. Grain sorghum yielded better in a soybean rotation than in monoculture and also in conventionally tilled seedbed than in conservation tillage. For other crops, yield did not differ significantly by tillage. Except for cotton, conventional tillage resulted in higher average net returns (NR) than conservation tillage. Although the most profitable system was continuous cotton with conservation tillage, NR varied widely across years, and there were fewer observations for cotton than for other systems in the study. Among conventional tillage seedbed preparation, nonirrigated continuous soybean was more profitable than any of the irrigated systems, including irrigated soybean. However, irrigated soybean resulted in NR that were less variable than nonirrigated soybean. The study confirmed the increased variable costs and decreased equipment costs that accompany conservation tillage systems. Even with the dramatic changes in burndown herbicide costs that have occurred since the study was conducted, the rankings of the cropping systems for profitability would not change.

INNOVATIVE REMOTE SENSING TECHNIQUES TO INCREASE NITROGEN USE EFFICIENCY OF CORN

Nitrogen (N) fertilizer recommendations made without adequate knowledge of the N supply capability of a soil can lead to ineffi-cient use of N. Proper crediting of N from manure and legumes as well as mineralization of N from organic matter is difficult. Remote sensing techniques that use the crop to indicate its N status show considerable promise for improving N management. Objectives of this paper were twofold: 1) to compare the N Reflectance Index (NRI) calculated from ground-based radiometer measurements acquired over irrigated corn (Zea mays L.) at a nadir view (0°) and an oblique view (75°) with measured plant N and 2) to evaluate the NRI obtained from both view angles for correcting in-season N deficiencies in a commercial corn field. The NRI calculated from canopy reflectance was not representative of plant N at the sixth leaf growth stage (V6) for either view angle because of the soil background influence on canopy reflectance. However, the oblique view NRI was a good predictor of plant N at V9 and V12 as was the nadir view NRI at V12. The nadir view NRI was not as sensitive as the oblique view NRI at the V9 growth stage because soil was still visible through the canopy. Consequently, the nadir view NRI provides a conservative estimate of plant N prior to complete canopy cover. Use of the nadir view NRI to detect in-season corn N deficiencies for the 1999 growing season reduced N application during the growing season by 39.2 kg N ha−1without reducing grain yield. If the oblique view NRI would have been used to assess the plant N status, the first fertigation would not have been recommended which would have saved additional N.

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) ...

Operative Calibration Methodology of a TDR Sensor for Soil Moisture Monitoring under Irrigated Crops

Time domain reflectometry (TDR) is more and more frequently used for soil water content measurements in replacement of other techniques as neutron probe. Such observations that can be continuously collected on dataloggers are convenient for monitoring water fluxes under irrigated crops. Though relationships to calculate volumetric water content from analysis of TDR signal and collected data are published in literature or given by manufacturers for different commercialized devices, the results are not satisfactory for many soils and specific calibrations are required. In replacement of the traditional calibration method, two rapid operative computer assisted methods are proposed. The first one is based on drip moistening of a cylindrical sample of disturbed dry soil in which a TDR sensor is vertically embedded. The second one uses the same cylindrical sample wetted close to saturation in which a TDR sensor is inserted step by step during measurements. The data from the two methods were fitted using second degree models. These results are in good agreement with conventional calibration method or gravimetric field measurements of soil water content. Utilization of short time step TDR measurements for monitoring soil water storage under a furrow irrigated corn shows consistent observations with water applications or uptakes by crop. Field comparison with neutron probe and gravimetric measurements corroborate the need of a specific calibration for the soil studied in this paper though its clay content is about 20%.

Irrigation management for corn in the northern Great Plains, USA

Irrigation management influences production costs and affects leaching of nutrients to groundwater. This study was conducted to compare irrigation scheduling techniques on a field-scale site and to determine whether significant irrigation water savings and equivalent yields could be achieved compared with the practices of other commercial growers in the local area. The effects of four irrigation scheduling techniques on seasonal irrigation water requirements and corn grain yields were studied for the 1990–1995 seasons at a field-scale (53.4 ha) site within the Oakes Test Area (OTA) of the Garrison Diversion Unit in southeastern North Dakota, USA. The four scheduling techniques, applied with field quadrants and seasons as dimensions of a modified Latin square statistical design, included irrigating based on tensiometer and infrared canopy temperature measurements, two water balance methods, and irrigating based on CERES–Maize estimates of plant-extractable soil water. No statistically significant differences in seasonal irrigation totals were found between irrigation scheduling methods or irrigation quadrants, while statistically significant differences were found for season. Corn grain yield was significantly affected by seasons, quadrants, and irrigation scheduling methods for both the current and previous seasons. Compared to other commercial growers in the OTA, this study maintained 5% higher yields and saved approximately 30% in irrigation inputs. Careful irrigation scheduling, based on any of the four techniques, offers the potential to reduce input costs for irrigated corn production in the area.

The Effect Of Municipal Solid Waste Compost Application On Soil Water and Water Stress in Irrigated Corn

Land application of municipal solid waste (MSW) compost increases soil organic matter content and influences soil physical properties. This study was conducted to measure the effect of compost on the water holding capacity of soil and water status in corn (Zea mays L.) from 1993 to 1995. The soil was a Hubbard loamy sand (sandy, mixed, Udorthentic Haploboroll) cropped to irrigated corn at the Sand Plain Research Farm at Becker, MN. Compost treatments on dry weight basis were 0 and 90 Mg ha−1 yr−1 from 1993 to 1995, and a one time application at 270 Mg ha−1 in 1993. The soil moisture retention curves were generated in 1994 and corn leaf water potential and soil bulk density were measured each growing season. Based on water retention curves, the addition of compost increased the water holding capacity of soil without significant increase in the estimated available water. This was contradicted by field measurements which showed that compared to a fertilized control one compost source at the 270 Mg ha−1 rate in the year of application increased plant water stress by 0.22 MPa, likely due to salt loading. In the year after the application of the 270 Mg ha−1, two compost sources increased soil water content and corn yield 0.14 cm3 cm−3 and 0.9 Mg ha−1 respectively. The yield increase was also associated with a reduction in plant water stress of 0.14 MPa due to one of the compost sources.

Demanda de irrigação suplementar para a cultura do milho no estado de Minas Gerais

Com o emprego de um modelo de balanço hídrico e de técnicas de sistema de informações geográficas, a demanda máxima diária de irrigação suplementar para a cultura do milho, no Estado de Minas Gerais, foi simulada e espacializada. Consideraram-se solos de textura grossa (disponibilidade total de água - DTA: 0,6 mm cm-1), média (DTA = 1,2 mm cm-1) e fina (DTA = 1,8 mm cm-1). As precipitações dependentes diárias foram estimadas em nível de 75% de probabilidade, utilizando-se a distribuição gama, enquanto a evapotranspiração diária foi em nível de 50% de probabilidade, utilizando-se o modelo proposto por Penman-Monteith (Smith, 1991). Identificou-se, espacialmente, a melhor época de plantio para o milho, considerando-se a menor demanda de irrigação.

Spatial and temporal variability of corn grain yield: site-specific relationships of biotic and abiotic factors.

Inadequate information on factors affecting crop yield variability has contributed to the slow adoption of site-specific farming (SSF). This study was conducted to determine the effects of biotic and abiotic factors on the spatial and temporal variability of irrigated corn grain yields and to derive information useful for SSF. The effects of water (80% evapotranspiration (ET) and 50% ET), hybrid (drought-tolerant and -susceptible), elevation, soil index (SI)(texture), soil NO3–N, arthropods, and diseases on corn grain yield were investigated at Halfway, TX on geo-referenced locations. Grain yields were influenced by interrelationships among biotic and abiotic factors. Grain yields were consistently high under high water treatment, at higher elevations, and on soils with high SI (high clay and silt). Soil NO3–N increased grain yields when water was adequate. Management zones for variable rate fertilizer and water application should, therefore, be based on information on elevation, SI, and soil NO3–N. The effects of arthropods, diseases, and crop stress (due to drought and N) on corn grain yield were unpredictable. Spider mite (Oligonychus pratensis) and common smut (Ustilago zeae) damage occurred under hot and dry conditions in 1998. Spider mite infestations were high in areas with high soil NO3–N. Moderate air temperatures and high relative humidity in 1999 favored southwestern corn borer (Diatraea grandiosella) and common rust (Puccinia maydis) incidences. Knowledge of conditions that favor arthropods and diseases outbreak and crop stress can improve the efficiency of scouting and in-season management of SSF. Management of SSF can be improved when effects of biotic and abiotic factors on grain yield are integrated and evaluated as a system.

Modelling irrigation scheduling to analyse water management at farm level, during water shortages

The area under irrigated corn has significantly increased in the Charente river basin during the last 10 years. Corn water requirements are maximum in the summer, the period with low water flows and highest environmental vulnerability. Periods of water shortage during which irrigation is temporarily forbidden occur frequently. To reduce water demand, specific water saving policies are required. This paper investigates irrigation management strategies at farm level during water shortages. A computer programme called IRMA is used to represent the farmer's decision making process. The model was calibrated and validated using information collected through a detailed monitoring of irrigation and farming practices of three representative farms during two irrigation seasons. The accuracy of the model was good; the difference between measured and simulated cumulative water volume used was slightly less than 8.5%. Analysis of daily simulated water demand shows that farmers have adopted different strategies to deal with water shortages, depending on the physical and socio-economic characteristics of their farms. The application presented in this paper stresses the potential of the proposed approach, if used on a larger farm sample, to compare the expected impact of different water management policies on water demand and irrigation practices at the farm level.

Water Use Efficiency of Different Maturity Corn Hybrids and Grain Sorghum in the Central Great Plains

In areas of finite groundwater resources, the groundwater used for irrigation must be used as efficiently as possible. Yields and water use characteristics of longer-maturity corn (Zea mays L.; 118-d relative maturity), shorter-maturity corn (97-d relative maturity), and grain sorghum [Sorghum bicolor (L.) Moench] under full and limited irrigation were evaluated from 1993 to 1996. Mean yield of longer-maturity corn was 15 bu/acre greater than that of shorter-maturity corn and 50 bu/acre greater than that of grain sorghum. Longer-maturity corn used the greatest amount of water, 3.4 in, greater than shorter-maturity corn or grain sorghum. Average water use rates were similar among the three crops. Mean water use efficiency for longer-maturity corn was not different from that of shorter-maturity corn; mean water use efficiency of grain sorghum was 1.4 bu/acre per in, less. Mean yield of fully irrigated crops was 15 bu/acre greater than that for crops under limited irrigation (replacing 70% of crop evapotranspiration [ET]). Water use efficiency of crops under limited irrigation was 0.7 bu/acre per in, greater than under full irrigation, but full irrigation of corn was more profitable than limited irrigation. These yields, average water use rates, and water use efficiencies indicate no justification for choosing shorter- over longer-maturity corn.

CONTROLLING GROUNDWATER QUALITY WITH ENDOGENOUS REGULATORY INSTRUMENTS

ABSTRACT. This research presents a competitive dynamic model that endogenously evaluates the economics of regulatory tax‐policy options. This model is then applied to an irrigated corn production area west of Kearney, Nebraska, where the average groundwater contamination level from nitrates is reported to be 8.7 parts per million (ppm). Results indicate that no regulatory policies are necessary for maintaining potable groundwater quality with either a surge‐flow irrigation system or a sprinkler irrigation system. In areas where conventional furrow irrigation technology is being used, higher net economic benefits result from the adoption of a variable‐tax on nitrogen fertilizer use, followed by a constant‐unit tax and a pollution tax.

Corn Yield Response to Tillage with Furrow Irrigation

Conservation tillage techniques have gained widespread, but not universal, use in irrigated corn (Zea mays L.) production. This study was conducted to evaluate yield impacts associated with conservation tillage methods when compared with conventional techniques in a replicated field experiment for 17 consecutive years in Nebraska (1976-1992). Six tillage treatments were imposed on continuous corn production and replicated three times. Tillage treatments ranged from traditional (disk and surface plant) to no-till (slot plant on existing ridge). Post-plant operations were uniformly applied to accommodate furrow irrigation. Over the life of the project the conservation tillage treatments (ridge till, rotary till, and slot plant) had a 4 bu/acre increase in grain yield over the conventional treatments (those having chisel, disk, or lister operations). The advantage of the conservation tillage systems was amplified by corresponding lower production costs. The rotary, ridge, and slot tillage systems had S7.72, S14.22, and $16.22/acre lower annual tillage and herbicide costs (1990 dollars), respectively, than the conventional tillage system with a disking operation. The conservation tillage treatments significantly lowered stalk rot and residual spring soil nitrate N concentrations. Other comparisons showing significant differences were list vs. chisel and disk for harvest population and soil potassium concentrations, and ridge vs. rotary for harvest population. None of the other comparisons tested had significant differences for grain yield or other soil parameters. Overall, this study indicates that conservation tillage on irrigated continuous-corn is advantageous over conventional methods.

Evaluation of the Root Zone Water Quality Model for Conditions in Central Nebraska

AbstractThe Root Zone Water Quality Model (RZWQM) was evaluated for a region that has a long history of irrigated corn (Zea mays L.). Imprecise irrigation and plentiful fertilizer applications have contributed to the buildup of NO3‐N in ground water, where concentrations often exceed 30 mg L−1. Experiments were conducted to evaluate the effects of management practices on corn yield, N uptake, plant biomass, leaf area development, soil water content, and soil N. Field‐measured results from 1992 were used to calibrate RZWQM. The model was evaluated by simulating three irrigation levels and five fertilizer rates for 1993 and 1994. The model simulated the soil water pattern satisfactorily during most of the growing season; however, the simulated soil profile water content was lower than field conditions in the spring and fall. Transpiration appears to be excessive when the leaf area index (LAI) is small. Simulated yields exceeded measured values, with the largest errors for small fertilizer applications in 1993 and for large fertilizer applications in 1994. The mean error between measured and modeled yields was 2.9 Mg ha−1, with a root mean square error (RMSE) equal to 46% of the mean yield for all treatments over the 3 years. Estimates of LAI and aboveground biomass were closer to measured values, with mean errors of 5% for leaf area and 1% for biomass. The relative RMSE for LAI and biomass was 26 and 17%, respectively. The model underestimated aboveground N uptake, with a mean error of 25 kg N ha−1 and a relative RMSE of 41%. While development of the comprehensive RZWQM has been constructive, improvements are still needed. Excessive depletions in the spring and fall overstate storage of off‐season precipitation, and this leads to underestimating annual leaching losses. Combining excessive yield predictions with low N uptake estimates exaggerates the N use efficiency. These discrepancies will have a profound effect on the simulated impact of management practices. Leaching losses and yield effects will be understated, which may lead to development of policies that affect producers more severely than the model implies.