Abstract

Vegetative reconstruction using alfalfa (Medicago sativa) has been effective in many areas to combat desertification. In arid regions of the China Loess Plateau water availability limits alfalfa productivity. Precipitation, runoff, soil moisture, and alfalfa biomass data from 2008 to 2010 on four distinct slopes representative of the Northern Shaanxi Loess Region, were collected. Relationships between precipitation, water availability, water use, and biomass were evaluated. Two methods - the Penman-Monteith-56 method and the water balance method, were used to estimate soil water carrying capacity for alfalfa and were compared. For alfalfa land on steep slopes, the relationship between water availability (Y_s) and precipitation (P) was Y_s = 0.8003P + 2.8568. Available water and alfalfa biomass had a linear correlation and alfalfa biomass and water use had a quadratic correlation. The Penman-Monteith-56 method estimated average annual water use of alfalfa to be 446.6 mm and peak alfalfa production to be 3992.2 to 4173.7 kg ha^-1. This method overestimated annual water use by 24.3 to 25.8% and biomass by 16.1 to 33.5%. Relationships between all measured parameters and recommendations for improving vegetative reconstruction are discussed.

Key words: Penman-Monteith-56 method, soil and water balance principle, Medicago sativa, water availability, desertification.