Experiment on water and nitrogen distribution in soils under ridgefurrow irrigation with ammonium nitrate solution
(1. Institute of Soil and Water Conservation, CAS & MWR, Yangling, Shaanxi 712100, China; 2. Institute of Watersaving Agriculture in Arid Areas of China, Northwest A&F University, Yangling, Shaanxi 712100, China; 3. University of Chinese Academy of Sciences, Beijing 100049, China)
Abstract: In order to provide guidance to reasonable design of irrigation technique and system in ridgefurrow intercropping fields, the infiltration characteristics and soil water and nitrogen distributions in four soil textures under ridgefurrow irrigation with ammonium nitrate solution were investigated in laboratory experimentally by using rectangular soil chambers to simulate the twodimensional infiltration in the irrigation. The distributions of water, nitrate, and ammonium in the soils were clarified. The soil wetting front was also recorded against infiltration time. The results showed that the cumulative infiltration of fertilizer solution and its infiltration rate tend to decrease with increase in clay content of soil texture because of greater soil specific surface area. Note that the increasing slope of the cumulative infiltration curve is significantly dependent of soil texture. The Horton infiltration model with three underdetermined parameters is fairy precise in estimating infiltration of fertilizer solution, in which the steadystate infiltration rate has very practical and is one important reference quantity for determining the flow rate in ridgefurrow irrigation. The wetted front migrates far away in the lateral and vertical directions in coarser soils at the same infiltration condition, the vertically wetted distance is longer than the laterally wetted one, and the wetted front is like an ellipsoid with a long axis in the vertical direction. The relation of laterally wetted distance to infiltration time can be described by an exponential function, while the vertically wetted distance has a linear relation to the square root of infiltration time. It was illustrated that the nitrate accumulates on the boundary of wetted front, but the highest ammonium concentration appears near furrows. The ridgefurrow fertigation technique should be implemented in finer soils to reduce deep percolation of water and nutrients below the root zone and improve water and fertilizer use efficiency in ridgefurrow intercropping fields.
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