种植密度对光敏型高丹草营养成分及动态变化的影响

在黄土高原雨养农业区,以光敏型高丹草品种“大卡BMR”和“海牛”为材料,采用8.33、12.50和16.67万穴·hm^-2 3个低、中、高密度全膜平铺穴播种植,在植株不同生长阶段,测定了粗蛋白(CP)、中性洗涤纤维(NDF)、酸性洗涤纤维(ADF)、总可消化养分(TDN)和糖锤度(BX)含量,以研究光敏型高丹草在当地的最佳种植密度和收获时期。结果表明:生长发育进程在植株营养形成过程中占主导地位。在品种间,两品种生长前期CP含量差异较大(P<0.05);“大卡BMR”的NDF、ADF和BX整体低于“海牛”,TDN含量高于“海牛”。密度对营养成分有影响,CP含量随密度的增大有所降低;密度对BX含量前期影响较大(P<0.05),中后期影响不明显(P>0.05);在全生长期内NDF和ADF含量整体上高密度处理明显低于(P<0.05)低密度处理;密度对TDN含量影响明显(P<0.05),生长后期(出苗后126~140 d)依次均为高密度>中密度>低密度。营养成分和产量的动态变化表现为,两品种随生长发育进程的延长,CP含量均呈逐渐下降的变化趋势,BX均呈逐渐上升的变化趋势,NDF和ADF含量均呈“升—降—升”的变化趋势,TDN含量均呈“降—升—降”的变化趋势;在出苗后126~140 d,干物质产量仍在上升,CP和TDN产量平稳,TDN的含量处于下降趋势。这种动态变化为北方不抽穗或能抽穗不能成熟的光敏型高丹草最佳刈割期的决策提供了重要依据。从饲草生产角度考虑,在春播一茬青贮收割模式下,当地以“大卡BMR”品种较好,种植密度以每公顷12.50万穴较好,两品种均在出苗后126~140 d(9月上中旬,大卡BMR处于抽穗期、海牛处于开花期)刈割最佳。

Effect of planting density on plant nutrients and their dynamics in PPS sorghum-sudangrass hybrids

This study investigated the optimum planting density and harvest date of photoperiod-sensitive (PPS) sorghum-sudangrass hybrids in the rain-fed farming region of the Loess Plateau. Two hybrids, “Big Kahuna BMR” and “Monster”, were planted with 3 different densities (83300, 125000 and 166700 holes·ha^-1) on double ridge soil covered with plastic-film fully mulched. The contents of crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), total digestible nutrient (TDN) and brix (BX) were measured in the plants at different growth stages. Results showed that the growth and development process played a major role in the formation of plant nutritional ingredients. The nutritional difference between the 2 varieties was more significant in the early than late growing stages. The NDF, ADF and BX contents of “Big Kahuna BMR” were all lower than “Monster”, while its TDN contents were higher. CP content declined with increased planting densities. BX contents were more influenced by density in the early than middle or late stages. For the entire growth period, NDF and ADF contents in higher density plantings were significantly lower. In the late growth period (126 to 140 d after seeding), TDN contents progressively decreased as density increased. As density increased, the 2 varieties’ CP contents gradually decreased during the growth process, while BX contents increased. NDF, ADF and TDN contents trended as ascent-descent-ascent from 70 to 140 d after seeding. In the final period of 126 to 140 d, dry matter yield continued to increase but CP and TDN contents did not change significantly (although TDN decreased slightly). These dynamic changes in nutrient content and yield indicate the best harvest date for PPS sorghum-sudangrass. In terms of forage production, the optimum variety for spring sowing with a one-cut system for silage is “Big Kahuna BMR”, with 125000 holes per hectare the preferred density. For both varieties, the optimum harvest period is between 126 to 140 d after seeding (in early or mid-September), when “Big Kahuna BMR” is booting and “Monster” is flowering.