The Impact of Different Levels of Nitrogen Fertigation and Irrigation on Nitrogen Leaching of Corn Silage

Abstract

The reduction of NO3--N contamination and increase in crop production depend upon proper management of irrigation and nitrogen fertilizer. To optimize crop management, it is necessary to evaluate all parameters that are involved in the soil nitrogen cycle, including the date, amount and type of nitrogen fertilizer and irrigation applications. The objective of this study was to evaluate the effect of different levels of irrigation and nitrogen management on nitrate leaching of corn grown for silage. The experiment included four levels of irrigation, e.g., 1.13 ETC, 1.0 ETC, 0.85 ETC, and 0.7 ETC, and three levels of nitrogen, e.g., 200 kg N ha--1, 150 kg N ha--1, and 0 kg N ha--1. The soil solution was sampled at a depth of 60 cm 24 hours after each irrigation and rainfall event. The nitrate concentration of each sample was determined to quantify the amount of NO3--N that was leached below the root zone. The NO3--N content of the soil up to the depth of 60 cm at planting and harvesting and the total nitrogen uptake by the crop were also determined. The amount of NO3--N leached below the depth of 60 cm in the 1.13 ETC and 1.0 ETC treatments with 200 kg nitrogen were 7.0 and 6.5 kg ha--1 and with 150 kg nitrogen applied were 8.4 and 3.1 kg ha--1, respectively. No nitrate leaching occurred from the 0.85 ETC and 0.7 ETC treatments. The major portion of the fertilizer that was applied for 0.85 ETC and 0.7 ETC treatments remained unused in the soil, while a small amount was taken up by the corn crop and the remainder was volatilized. Increasing the amount of fertilizer resulted in an increase in nitrogen uptake but reduced the ratio of plant uptake to total nitrogen applied. The amount of nitrate leaching significantly increased in response to an increase in the amount of fertilizer applied in the 1.13 ETC treatments. N leaching was controlled by irrigation and fertilizer management for the 150 and 200 kg nitrogen levels at full and over irrigation treatments, but a portion of N was lost as volatilization or remained in the soil at deficit irrigation levels. Irrigation should be based on crop demand, such as ETc, rather than a fixed application rate. Fertilizer should be applied through the irrigation system and should also be based on crop demand. In this experiment, N uptake decreased and nitrogen volatilization and final soil nitrogen increased for the deficit irrigation treatments as compared to the full irrigation treatments. Therefore, in order to avoid nitrogen loss, the amount of nitrogen fertilizer application should be reduced in proportion to the severity of the existing water stress condition.