Grazing height targets for Alexandergrass pastures under continuous stocking in integrated crop-livestock system

ABSTRACT: The aim of this experiment was to identify grazing height targets for Alexandergrass pastures under continuous stocking in integrated crop-livestock system (ICLS). For this purpose, twelve pastures were cultivated into an ICLS area, and maintained at 10, 20, 30, or 40 cm using grazing goats. The following variables were analyzed: leaf and herbage mass, accumulation rate, and allowance; leaf:stem ratio; chemical composition of hand-plucked samples; stocking rate; average daily gain and gain per area. The data were submitted to regression and correlation analysis. Significance was set at 5% (P≤0.05). The main results were: i) herbage and leaf lamina mass increased linearly with grazing height, and pastures maintained at 20 cm already presented the minimum amount recommended for soil cover in ICLS; ii) animal performance achieved an upper asymptotic plateau in pastures maintained around 30-40 cm and it was highly correlated with both grazing height and forage availability (mass and allowance). Alexandergrass pastures under continuous stocking in ICLS should be maintained between 30-40 cm to improve both cover crop biomass and animal performance.摘要：本试验旨在明确农牧综合生产系统（integrated crop-livestock system, ICLS）中采用连续放牧模式的亚历山大草（Alexandergrass）牧场的适宜放牧高度目标。为此，在ICLS区域内设置12块试验牧场，通过放牧山羊将牧场高度分别维持在10、20、30或40 cm。本试验分析的指标包括：叶片与牧草生物量、积累速率及饲草供给量；叶茎比；手采样品的化学成分；放牧率；平均日增重及单位面积增重。所有数据均进行回归与相关性分析，显著性阈值设定为5%（P≤0.05）。主要结果如下：① 牧草与叶片生物量随放牧高度呈线性增长，维持在20 cm的牧场已达到ICLS中土壤覆盖推荐的最低阈值；② 当牧场维持在30~40 cm左右时，家畜生产性能达到渐近上限平台，且该性能与放牧高度及饲草可获得量（生物量与供给量）呈高度相关。综上，ICLS中采用连续放牧模式的亚历山大草牧场应维持在30~40 cm，以同时提升覆盖作物生物量与家畜生产性能。