Nitrate‐Nitrogen Leached Below the Root Zone During and Following Alfalfa

Abstract

The nitrate-nitrogen (N0,-N) contribution to subsurface drainage water by irrigated alfalfa (Medic:ago satire L.) in crop rotations was evaluated by measuring the soil water flux and NON-N concentration below the root zone of alfalfa and crops following alfalfa with and without additional nitrogen fertilization. Under alfalfa grown on Portneuf silt loam (Durixeroilic Calciorthid) with a permeable hardpan, 44 kg NO,-N he year ' moved below the root zone at concentrations betWeen 3 and 15 ppm. During the growing season following alfalfa, 85-96 kg NO,-N he year' moved below the root zone under nonferdlized bean (Phaseolus vulgaris) crops at concentrations between 1 and 83 ppm. The second growing season after alfalfa, 17-29 kg NO,-N he year' at 3-15 ppm NO,-N moved below the root zone of nonfertilized bean and wheat (Tridezun aeitiVillit L.) crops. A field planted to corn (Zea mays L.) and fertilized with 200 and 170 kg N ha-' the first and second year after alfalfa lost 153 and 108 kg NO-N he, respectively, from leaching. Leachate N concentrations varied from 1 to 64 ppm. Unfertilized corn lost 60 and 17 kg NO,-N/ha the first and second year after alfalfa, respectively, at leachate concentrations of 1-31 ppm. The NO,-N concentration in the soil solution below only slightly permeable hardpan areas was between 13 and 67 ppm, but only 10-23 kg he year' moved below the root zone because of the lower water flux through the hardpan. Comparing these results with previous data for the same area suggests that considerable denibifkation and/or dilution takes place at the water table interface since 5.2 ppm NO,-N was the highest concentration measured in the subsurface drainage water with an average of 3.2 ppm NO,-N. The NO,-N contributed by alfalfa in the crop rotation was estimated to equal just half of that accounted for in the subsurface drainage in a previous study on the same irrigated tract.' Contribution from the USDA-SEA-ARS; Univ. The potential health hazards of nitrate nitrogen (NO,-N) in surface and subsurface water has drawn increased public attention to agricultural practices as a possible source of nonpoint source NO 3-N water pollution. Because high NO,-N concentrations in drinking water are considered to pose health hazards to livestock and humans, particularly infants, the U.S. Public Health Service has set a maximum of 10 ppm NO,-N as the standard for drinking water (13). The high NO3-N levels found in some areas may come from any of several sources, and the sources must be idenified if management practices are to be changed to reduce nonpoint NO,-N sources entering subsurface, and eventually, surface waters. Nitrate leaching rates are a function of irrigation and precipitation rate and timing, nitrogen fertilizer application rate and timing (1, 6), and the crops grown (9, 12).Alfalfa (Medicago sativa L.) removes water and NO,-N from deeper in the soil profile than other crops (2,7,11), and is an excellent NO 3 scavenger for reducing the amount of NO3-N leaching following a high N fertilized crop, o...

Nitrogen dynamics under growth chamber conditions as influenced by method of alfalfa termination 2. Plant-available N release

“…However, poor synchrony between N release from legume residues and crop N demands may reduce the fertility benefits of the legume (Huntington et al 1985;Westermann and Crothers 1993). Moreover, this lack of synchrony may result in the accumulation in soil of plantavailable N which may then be prone to loss by leaching and denitrification (Robbins and Carter 1980;Firestone 1982;Campbell et al 1994).…”

Furrow Irr Igation and N Management Strategies to Protect Water Quality

“…This doubling suggests that corn did not use fertilizer N efficiently from this broadcast/sidedress treatment. This treatment's additional 230 kg N ha--1 at season's end was susceptible to leaching that could occur in the winter (Wright et al, 1998) or the following spring (Robbins and Carter, 1980). Profile N totals were not different (P>0.43) from season start to end for any other N placement near either the furrow inlet or outlet in 1989 (Fig.…”

“…In semi-arid areas, nitrate leaching is usually greatest from heavily irrigated profiles that a) have been fertilized excessively (Ayars and Tanji, 1999;Robbins and Carter, 1980) or b) contain much residual N from previous cropping (Robbins and Carter, 1980). From 50 to 150 kg NO 3-N ha-1 can be lost from southern Idaho silt loams during the non-growing season, even with relatively little winter drain-age (Wright et al, 1998).…”

“…From 50 to 150 kg NO 3-N ha-1 can be lost from southern Idaho silt loams during the non-growing season, even with relatively little winter drain-age (Wright et al, 1998). In Idaho and elsewhere, residual and recently mineralized NO3-N can be leached by late-season irrigations (Wright et al, 1998) or an early-season irrigation just before planting (Meek et al 1995;Robbins and Carter, 1980). Irrigation must be well managed to efficiently use N fertilizer applied at nominal, economic rates (Keeney, 1982;Robbins and Carter, 1980;Russelle et al, 1981).…”

“…In Idaho and elsewhere, residual and recently mineralized NO3-N can be leached by late-season irrigations (Wright et al, 1998) or an early-season irrigation just before planting (Meek et al 1995;Robbins and Carter, 1980). Irrigation must be well managed to efficiently use N fertilizer applied at nominal, economic rates (Keeney, 1982;Robbins and Carter, 1980;Russelle et al, 1981). In western Idaho, many producers apply large amounts of N to onion (Allium cepa) to compensate for leaching and denitrification losses from excessive irrigation (B.D.…”