The nitrogen loss in drained soils

Abstract

We need to understand the effects of present-day agricultural production technology on chemical movement within and from watersheds. The soils and climate within a watershed, within a region, or both affect the movement of chemicals through the watersheds. The amounts of agricultural chemicals reaching the water sources are difficult to quantify since chemical loads usually cannot be directly measured or calculated with much confidence from water quality monitoring data. Estimation techniques or deterministic models simulating the water and chemical movement processes are useful tools to assess the magnitude of water pollution in large watersheds.Two computer simulation models were used in this study. The CREAMS model (Knisel, 1980) was used to predict the volume of drainage and NO3-N loads in the water; the DRAINAGE model (Kanwar et al., 1983) was used as a check on the CREAMS model. Weather data for 23 years from Humboldt County in north-central Iowa were used in the model simulations to estimate the effect of various agricultural management practices on the quality of drainage water. The results of this simulation study show that larger applications of nitrogen fertilizer resulted in larger nitrate losses through subsurface drainage. Nitrate-nitrogen leaching losses were considerably less under a corn-soybean rotation than under continuous corn production; this difference shows that crop production activities and fertilizer management practices can make a significant impact on the quality of drainage water from agricultural watersheds.