Root Function in Nutrient Uptake and Soil Water Effect on NO3−-N and NH4+-N Migration

Root function in uptake of nutrients and the effect of soil water on the transfer and distribution of NO3−-N in arable soil were studied using summer maize (Zea mays L. var. Shandan 9) as a testing crop. Results showed that root growth and water supply had a significant effect on NO3−-N transfer and made NO3−-N distributed evenly from bulk soil to rhizosphere soil. Under a natural condition with irrigation, the difference of NO3−-N concentration at different distance points from a maize plant was smaller, while obvious difference of NO3−-N concentration was observed under conditions of limited root growth space without irrigation. Whether root growth space was restricted or not, the content of soil NO3−-N decreased gradually from 10 to 0 cm from the plant, being opposite to the root absorbing area in soils. When root-grown space was limited, changes of NO3−-N concentration at different distances from a plant were similar to that of water content in tendency. Results showed that NO3−-N could be transferred as solute to plant root systems with water uptake by plants. However, the transfer and distribution of NH4+-N were not influenced by root growth and soil water supply, being different to NO3−-N.