Beef cattle performance on signal grass pastures deferred and fertilized with nitrogen

ABSTRACT The effect of four nitrogen levels (0, 40, 80 and 120kg N ha-1), applied before deferment on the beef cattle production and structural variables on Urochloa decumbens (signal grass) were assessed from January to October 2012 and from January to September 2013. A randomized block design with three replicates was adopted, in an arrangement of repeated measures in time (grazing period). An interaction effect between nitrogen level and grazing period was observed on extended-plant height and herbage mass. As the nitrogen levels were increased, extended-plant height, herbage mass, total herbage allowance, and efficiency of conversion of fertilizer into herbage were increased. Throughout the grazing period, pasture height, extended-plant height, percentage of leaves, herbage and morphological components allowance, and percentages of leaves and stems in the herbage apparently selected by the animal decreased. Nitrogen levels had no effect on average daily gain or gain per area in the first year. A fixed deferment period with increasing levels of nitrogen fertilization on signal grass pastures does not influence the average daily gain per animal, reduces the efficiency of the nitrogen fertilizer and negatively changes the structural characteristics of the pasture.摘要 本研究于2012年1月至10月及2013年1月至9月期间，评估了休牧前施用的4个施氮水平（0、40、80和120 kg N·ha⁻¹）对俯仰臂形草（Urochloa decumbens，signal grass）牧场的肉牛生产性能及结构性状的影响。试验采用随机区组设计，设置3次重复，并以放牧周期为时间单元开展重复测量。研究发现，施氮水平与放牧周期之间存在显著交互作用，对伸长株高及牧草生物量产生影响。随着施氮水平提升，伸长株高、牧草生物量、总牧草供给量以及肥料牧草转化效率均显著升高。在整个放牧周期内，草层高度、伸长株高、叶片占比、牧草及形态组分供给量，以及动物表观采食牧草中叶片和茎秆的占比均呈下降趋势。试验第一年，施氮水平对肉牛平均日增重及单位面积增重均无显著影响。综上，在信号草牧场采用固定休牧期并提升施氮水平，不会影响单只肉牛的平均日增重，但会降低氮肥利用效率，并对牧场结构性状产生负面影响。