Quantification of the interactive effects of nitrogen (N) and water on nitrate (NO3) loss provides an important insight for more effective N and water management. The goal of this study was to evaluate the effect of different irrigation and nitrogen fertilizer levels on nitrate-nitrogen (NO3-N) leaching in a silage maize field. The experiment included four irrigation levels (0.7, 0.85, 1.0, and 1.13 of soil moisture depletion, SMD) and three N fertilization levels (0, 142, and 189 kg N ha-1), with three replications. Ceramic suction cups were used to extract soil solution at 30 and 60 cm soil depths for all 36 experimental plots. Soil NO3-N content of 0�30 and 30�60-cm layers were evaluated at planting and harvest maturity. Total N uptake (NU) by the crop was also determined. Maximum NO3-N leaching out of the 60-cm soil layer was 8.43 kg N ha-1, for the 142 kg N ha-1 and over irrigation (1.13 SMD) treatment. The minimum and maximum seasonal average NO3 concentration at the 60 cm depth was 46 and 138 mg l-1, respectively. Based on our findings, it is possible to control NO3 leaching out of the root zone during the growing season with a proper combination of irrigation and fertilizer management.
Abbreviations AN30, sum of initial NO3-N for the 0�30 cm soil depth, N in irrigation water and applied N fertilizer;
AN60, sum of initial NO3-N for the 0�60 cm soil depth, N in irrigation water and N fertilizer;
Bd, bulk density;
CNC, crop N content;
CSC, ceramic suction cup;
DAP, days after planting;
ET, evapotranspiration;
ETO, reference evapotranspiration;
FC, field capacity;
ID, applied water;
NLIR, NO3-N leaching rate;
NO3-NL30, total NO3-N leached out of 30-cm soil layer;
NO3-NL60, total NO3-N leached out of the 60-cm soil layer;
NO3-NL30G, NO3-N leached out of the 30-cm soil layer during crop season;
NU, crop nitrogen uptake;
NUE, nitrogen use efficiency;
P-M, Penman-Monteith;
PWP, permanent wilting point;
SMD, soil moisture depletion;
TN, soil initial N plus irrigation water N plus applied fertilizer N
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