Forage potential of sorghum-clover intercropping systems in semi-arid conditions

ABSTRACT To identify the optimum intercropping system of sorghum and clover in terms of quantity and quality of forage yield, a two-year experiment was conducted in a semi-arid region of Iran, during the 2016 and 2017 growing seasons. Treatments consisted of eight cropping systems: S75C25 (75% sorghum + 25% clover), S50C50 and S25C75, as replacement series; S100C50, S50C100, and S100C100 as additive series; and sole cultures of sorghum and clover. The highest and lowest dry matter (DM) yield (29.17 and 10.71 Mg·ha-1) were found in the S100C100 and clover monoculture systems, respectively. Although the highest content of crude protein (CP) and digestible dry matter (DDM) were recorded from clover monoculture, the maximum yield of CP and DDM were obtained from the S100C100. Increasing the proportion of clover in intercropping decreased the acid detergent fiber and neutral detergent fiber, increased the relative feed value, net energy for lactation and dry matter intake. Increasing the proportion of sorghum in intercropping improved the yield of DM, CP and DDM. The land equivalent ratio for DM yield was higher than one in all intercropping treatments but were significantly higher in the additive intercropping systems. Overall, it could be concluded that sorghum and clover additive intercropping systems increased forage yield and quality, however if simultaneous increase of the quantity and quality of forage is the interest of this study then the S100C100 system had a significant advantage over other treatments and can be a suitable alternative for sorghum and clover monoculture systems in semi-arid regions.摘要：为探究饲草产量与品质最优的高粱-白三叶间作体系，本研究于2016及2017年生长季在伊朗半干旱区域开展了为期两年的田间试验。试验共设置8种种植体系：替代系列体系包括S75C25（75%高粱+25%白三叶）、S50C50、S25C75；加性系列体系包括S100C50、S50C100、S100C100；以及高粱单作与白三叶单作体系。S100C100体系与白三叶单作体系的干物质（dry matter, DM）产量分别达最高（29.17 Mg·ha⁻¹）与最低（10.71 Mg·ha⁻¹）。尽管白三叶单作体系的粗蛋白（crude protein, CP）与可消化干物质（digestible dry matter, DDM）含量最高，但S100C100体系的CP与DDM总产量最高。间作体系中白三叶占比提升可降低酸性洗涤纤维与中性洗涤纤维含量，同时提高相对饲用价值、泌乳净能与干物质采食量；而高粱占比提升则可提高DM、CP与DDM的总产量。所有间作处理的干物质产量土地当量比均大于1，其中加性间作体系的土地当量比显著更高。综合而言，本研究可得出如下结论：高粱-白三叶加性间作体系可提升饲草产量与品质；若以同步兼顾饲草产量与品质提升为目标，则S100C100体系相较其他处理具有显著优势，可作为半干旱区域高粱与白三叶单作体系的适宜替代方案。