Evaluation on comprehensive ecological benefits of different hedgerow patterns on slope-farmland in purple soil area

Hedgerow patterns have been used to control soil and water loss, agricultural non-point source pollution (especially nitrogen and phosphorus from slope-farmlands) in hilly areas. A comprehensive and rational evaluation of the ecological benefits of hedgerow patterns in slope-farmlands was critical for further evaluating eco-economic and social benefits of hedgerows. This has been deemed necessary for promoting and popularizing the application of optimized hedgerow patterns in hilly areas. However, critical questions (e.g., the use of unilateral evaluation indexes) have persisted relative studies on evaluation of the ecological benefits of hedgerow. These indexes have generally not accounted for controlling agricultural non-point source pollutants. Hence this paper established an evaluation index system including indexes for soil and water loss, agricultural non-point pollutants, anti-erosion forces and land productivity. It also evaluated the comprehensive ecological benefits of Amorpha fruticosa, Vetiveria zizaniodes, Medicago sativa and Eulaliopsis binata hedgerow patterns on slope-farmlands of the southwestern purple soil zone. The weights of the evaluation indexes were integrated in analytical hierarchy process and entropy weight decision-making calculations. The results showed a significant increase in comprehensive ecological benefits. The indexes for comprehensive ecological benefit (A), soil and water conservation one (B₁), agricultural non-point source pollutant control (B₂), soil anti-erosion force (B₃) and land productivity (B₄) of hedgerow patterns increased by 206.4% 301.9%, 228.6% 278.4%, 212.6% 346.6%, 93.7% 126.0% and 23.6% 35.8%, respectively, compared with the conventional cross-slope farming pattern. The order of different type ecological benefits for hedgerow patterns was B₂ (1.165) > B₁ (0.962) > B₄ (0.495) > B₃ (0.332). The order of improvement of comprehensive ecological benefits for different hedgerow patterns was A. fruticosa > V. zizaniodes Vetiver on 20° slope-farmland, M. sativa > E. binata in 13° slope-farmland. The mean increase in comprehensive ecological benefit of hedgerow patterns on 20° slope-farmland was 295.0%, which was higher than that of 13° slope-farmland by 211.0% over the conventional cross-slope farming pattern. Therefore maintaining shrub hedgerow patterns on slope-farmlands of southwest purple hilly region (especially on lager than 20° slope- farmlands) greatly increased the comprehensive ecological benefits.