Evaluation of Nitrogen and Irrigation Management for Corn Production using. Water High in Nitrate1. D. L. MARTIN, D. G. WATTS, L. N. MIELKE, K. D. FRANK, ...
Evaluation of Nitrogen and Irrigation Management for Corn Production using Water High in Nitrate1 D. L. MARTIN, D. G. WATTS, L. N. MIELKE, K. D. FRANK, AND D. E. EisENHAUER 2 ABSTRACT
some small municipalities are faced with the prospect of abandoning their domestic wells because concentrations exceed U.S. Public Health Service maximum standards of 10 ppm. A sizable portion of the accumulation of NO3~-N in the groundwater appears to be the result of N loss from irrigated corn (Zea mays L.) fields. The problem is generally most severe in areas where furrow irrigation is practiced on loamy sands or sandy loam soils but also occurs on finer-textured soils. There is growing pressure on farmers to modify management practices to reduce the NO3~-N leaching losses from agricultural lands. Producers are now faced with the question of how best to alter traditional management to minimize nitrogen (N) leaching losses while maintaining profitable yields. Interim guidelines have been established to aid producers in the decision making process. However, much remains unknown about the interaction of irrigation and N management practices in situations where increasing amounts of N are available in the irrigation water. To supplement ongoing field research in this problem area, we have used a field-calibrated computer model to estimate what the N uptake, leaching loss, and uptake efficiencies of fertilizer and groundwater N sources might be for a range of nitrogen-water management practices and groundwater NO3~-N concentrations. The utility of the model study is threefold: (i) it provides a better understanding of the contribution of the various N sources to uptake and leaching losses as management and groundwater NO3~-N concentrations change; (ii) it helps clarify how management can be best modified to minimize environmental impact; and (iii) it projects management practice effect on N uptake which may affect yield. The results of simulation studies must be viewed in a relative sense, recognizing that they are subject to all of the errors and approximations inherent in attempts to model complex systems.
A field-calibrated computer model was used to study the interaction of nitrogen (N) and water management for corn (Zea mays L.) production on sandy soils in the central Platte Valley of Nebraska. Most irrigation in this area is with pumped groundwater which at many locations contains from 10 to 30 ppm (or more) of nitrate nitrogen (NO3~-N). Simulation results were used to estimate the effects of irrigation management, N management, and the NO, -N concentration of the irrigation water upon N uptake by corn, the uptake efficiency of groundwater and fertilizer N, and the potential for pollution of groundwater with NO3~-N. Nitrogen uptake was also partitioned according to N source (groundwater N, applied fertilizer N, and residual plus mineralized N). Simulation results showed that: 1) Nitrogen uptake was strongly influenced by the amount of fertilizer N and irrigation water applied, and to a lesser extent by the NO3~-N concentration of the irrigation water. There was also a strong interaction of these parameters in determining N uptake. 2) The uptake efficiency of fertilizer N was very sensitive to excess irrigation and only slightly affected by the amount of fertilizer applied or the NO3~-N concentration of the irrigation water. 3) The uptake efficiency of groundwater N was strongly affected by the amount of irrigation water applied and the NO, -N concentration of the water while the amount of fertilizer applied had a lesser effect. In general, groundwater uptake efficiencies were higher and more stable than fertilizer uptake efficiencies. 4) Excess irrigation increased N uptake from groundwater sources under certain conditions. The groundwater N contribution to uptake was large for irrigation water containing >10 ppm NO3~-N and was primarily determined by the amount of irrigation and the NO, -N concentration. For 25 ppm NO,~-N irrigation water and small fertilizer applications more N was extracted from the groundwater through irrigation than was lost due to leaching. Additional Index Words: groundwater nitrogen, fertilizer nitrogen, nitrogen uptake efficiency, groundwater pollution, partitioning of nitrogen uptake. Martin, D. L., D. G. Watts, L. N. Mielke, K. D. Frank, and D. E. Eisenhauer. 1982. Evaluation of nitrogen and irrigation management for corn production using water high in nitrate. Soil Sci. Soc. Am. J. 46:1056-1062.
PROCEDURE The model used in this study is that of Watts and Hanks (1978). It describes the net changes of N in the root system of irrigated corn on sandy soil due to transformations, movement, and plant uptake for different water management practices. The model was modified to include NO3~-N contained in the groundwater as a N source, to simulate water and solute flow in layered soils, to simulate the application of anhydrous amonia (NH3), and to use growing degree days rather than calendar days as a time base for several physical-biological processes (Martin, 1979). The simulation model is site specific in that it requires soil-moisture release data, hydraulic conductivity data, initial N distribution within the soil profile, and several other soil-specific constants to simulate N uptake and leaching. Field experiments were conducted at two sites near the towns of Clarks and Bellwood in the summer of 1978 to provide calibration and verification data for the model. At the Clarks site the soil is a Fonner sandy loam (a
ROUNDWATER is the primary source of irrigation water in the Platte River Valley in central and eastern Nebraska. Currently, there are over 11,000 irrigation wells in the valley with the majority of these having pumping lifts
