Productivity and nutritive value of elephant grass pastures under organic and conventional production systems

Abstract: Elephant grass (EG) (Pennisetum purpureum Schum.) have great importance in tropical and subtropical climates, especially on dairy farms. Normally, EG is established alone under high fertilization levels. EG in organic production system can improve low production costs and environmental issues, are still little known. The aim of this research was to evaluate the performance of herbage yield, nutritive value, extraction/ export nutrient and forage yield and animal responses. Three production systems of EG were analyzed: (i) EG mixed spontaneous-growing species (SGE) in warm-season and ryegrass (R) in cool-season under organic production; (ii) EG mixed SGE + R under conventional system (positive control); and (iii) EG based under conventional production (control). Holstein cows were used in a rotational stocking. Forage samples were collected to evaluate the pasture and animal responses. Seven grazing cycles were performed during the experimental period (312 days). Herbage yield, forage intake, and stocking rate were 12548; 10270; 19168 kg ha-1 and 2.5; 2.6; 2.7% and 3.3; 2.1; 4.5 AU ha-1 day-1, respectively. Crude protein of EG was 17.9; 15.4; 16.4%, respectively. Mixed pastures, in conventional and organic production, had a better forage distribution throughout the seasons. Highest forage yield and extraction/ export nutrient was reported in pure EG within the conventional system.

摘要：象草（Elephant grass, EG）（Pennisetum purpureum Schum.）在热带与亚热带气候区域具有重要应用价值，尤其在奶牛养殖场均应用广泛。传统种植模式下，象草多在高施肥水平下单一种植。而有机生产体系中的象草种植方式，虽可降低生产成本、改善环境问题，但其相关应用效果仍鲜有研究。本研究旨在评估象草的牧草产量、营养价值、养分吸收/输出量，以及饲用表现与动物饲喂响应。
本研究共分析3种象草种植体系：（i）有机生产体系下，暖季混播自然生长物种（spontaneous-growing species, SGE）与冷季黑麦草（ryegrass, R）的象草混播模式；（ii）常规生产体系下，象草与SGE+R混播模式（阳性对照组）；（iii）常规生产体系下的纯象草种植模式（空白对照组）。
试验采用轮牧（rotational stocking）方式饲养荷斯坦奶牛（Holstein cows），采集牧草样本以评估牧场表现与动物饲喂响应。试验周期共计312天，共完成7个放牧周期（grazing cycles）。结果显示，牧草产量、饲草采食量（forage intake）与载畜率（stocking rate）分别为12548、10270、19168 kg·ha⁻¹，以及2.5%、2.6%、2.7%，和3.3、2.1、4.5 AU·ha⁻¹·d⁻¹；三个体系下象草的粗蛋白（crude protein）含量分别为17.9%、15.4%、16.4%。
常规与有机生产体系下的混播牧草地，全年饲草分布更为均匀。常规生产体系下的纯象草种植模式，其牧草产量与养分吸收/输出量均为最高。