Incorporation of Soil Bulk Density in Simulating Root Distribution of Winter Wheat and Maize in Two Contrasting Soils

Root length density (RLD) in a soil profile is an important factor in determining the root uptake of water and nutrients from soil. Accurate descriptions of the RLD distribution are important in developing models to simulate the flux of water and nutrients in fields. However, the normal vertical root length distribution in a soil profile is usually disrupted because of soil heterogeneity. This study used field-measured RLD of winter wheat (L.) and maize (L.) from two soils in the North China Plain from 2007 to 2010 to examine the effects of soil physical characteristics on the RLD distribution of the double-cropping system. The results showed that RLD distribution pattern was significantly affected by soil bulk density under sufficient water supply. The existence of a hard soil pan under the tillage layer greatly influenced the distribution curve of the RLD. Without bulk density modification, there was an apparent difference between measured and modeled RLD resulting in either overestimating or underestimating root length at certain soil depths. Introducing bulk density into an RLD simulation model significantly reduced the errors of simulated and measured RLD throughout the root zone profile.