Optimization of plant coverage in relation to water balance in the Loess Plateau of China

Abstract

A series of revegetation practices have been implemented to improve the environmental quality and to reduce water and soil losses in the wind and water erosion transitional belt of China's Loess Plateau. An incompatibility exists between the limited water availability and the extensive plant coverage needed to protect the soil from accelerated erosion. The objective of this study was to investigate the relationship between plant coverage and soil water to determine the optimal plant coverage for the two dominant shrubs (Caragana korshinkii Kom and Salix psammophila) in this area. Experiments were performed with four coverage treatments (T0, T1, T2, and T3) for each shrub during the growing seasons of 2008, 2009 and 2010. Soil water content was measured with a neutron probe. The Simultaneous Heat and Water Transfer (SHAW) model was used to simulate soil water content variations for a critical climatic year, i.e. the one-in-ten dry year. The soil and plant parameters of the SHAW model were calibrated using the measured soil water content in the 0–200cm soil layer of the T2 coverage for each species. The calibrated model was verified using measurements for T0, T1, and T3 plant coverages. The results indicated that soil water storage in the 0–200cm soil layer decreased with increasing plant coverage. Soil desiccation occurred at various depths in the 0–200cm soil layer for the different plant coverages. The degree of soil desiccation was greater for the two shrubs when plant coverage was more extensive. The SHAW model, calibrated for soil and plant parameters, accurately simulated soil water variations in the 0–200cm profile under different plant coverages. During the verification phase, the root mean square error (RMSE) between the measured and simulated soil water contents ranged from 0.022 to 0.033cm3cm−3 and the relative root mean square error (RRMSE) ranged from 14.4% to 24.6%. Based on the observed and modeled interactions of soil water depletion and plant growth, the optimal plant coverage corresponds to a maximum LAI of 1.27 for C. korshinkii and 0.70 for S. psammophila.