Optimization of plant coverage in relation to water balance in the Loess Plateau of China Wei Fu a, b , Mingbin Huang a, ⁎, Jacques Gallichand c , Mingan Shao a a State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F University, Shaanxi 712100, China b Key laboratory of Mollisols Agroecology, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin 150081,China c Département des Sols et de Génie Agroalimentaire, FSAA, Université Laval, Québec, Canada abstract article info Article history: Received 23 March 2011 Received in revised form 16 December 2011 Accepted 19 December 2011 Available online 3 February 2012 Keywords: Soil water balance Optimal plant coverage Semi-arid area Soil erosion Loess Plateau A series of revegetation practices have been implemented to improve the environmental quality and to re- duce water and soil losses in the wind and water erosion transitional belt of China's Loess Plateau. An incom- patibility 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 cover- age 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 con- tent in the 0–200 cm 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 0–200 cm soil layer decreased with increasing plant coverage. Soil desiccation occurred at various depths in the 0–200 cm 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 0–200 cm profile under different plant coverages. During the verification phase, the root mean square error (RMSE) between the measured and sim- ulated soil water contents ranged from 0.022 to 0.033 cm 3 cm -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. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The wind and water erosion transitional belt of China's Loess Plateau experiences intensive soil erosion, vegetation degradation, and soil desertification (Cha and Tang, 2000; Tang, 2000). The Chinese Government has implemented vegetation restoration prac- tices, e.g. planting perennial shrubs and grasses, to improve the envi- ronmental quality and to reduce water and soil losses in the area. In this semi-arid region, however, an incompatibility exists between the limited soil water availability and the extensive plant coverage re- quired for protecting the land (Xia and Shao, 2008). Increasing plant coverage can significantly reduce the sediment yield and effectively control soil erosion (Cerdá, 1999; Elwell and Stocking, 1976; Morgan et al., 1997). Snelder and Bryan (1995) investigated the relationship between plant coverage and soil loss under simulated rainstorms. They found that soil loss was the maxi- mum for plant coverages less than 25%, and that a minimum of 55% plant coverage was required to achieve satisfactory soil erosion con- trol. García-Ruiz et al. (1995) and Molinillo et al. (1997) showed that in the mountainous northern Spain, soil loss increased rapidly when reducing plant coverage, and that little soil loss occurred for shrub coverages greater than 40%–60%. In the northern China Loess Plateau, Guo and Shao (2009) showed that sediment yield was in- versely proportional to plant coverage of C. korshinkii, and that this inverse relationship could be expressed by a sigmoid function. However important plant coverage is for soil erosion control, the maximum plant coverage is determined by soil water availability. In China's Loess Plateau, extensive plant coverages were achieved dur- ing vegetation restoration efforts at the cost of severe soil desiccation and formation of dry layers. Soil desiccation can have a detrimental effect on the environmental and hydrological processes (Chen et al., 2008; Wang et al., 2010). For example, soil desiccation promotes Geoderma 173-174 (2012) 134–144 ⁎ Corresponding author at: Northwest A&F University, Yangling, Shaanxi 712100, China. Tel.:+86 29 87019071; fax: + 86 29 87012210. E-mail address: hmingbin@yahoo.com (M. Huang). 0016-7061/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.geoderma.2011.12.016 Contents lists available at SciVerse ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma