INDEX OF HORIZONTALITY AND REMOVAL OF TISSUES FROM MARANDU PALISADE GRASS

Abstract Possibly, the greater availability of nutrients in the soil will promote a more pronounced modification of the growth form of forage plant under high frequency of defoliation. To test this hypothesis, we characterized the changes in the growth form of Brachiaria brizantha cv. Marandu syn. Urochloa brizantha cv. Marandu (marandu palisade grass) submitted to cutting intervals and fertilization, as well as the effect of these modifications on the forages removed and remnant from the cut. This study was carried out in two experimental periods. In each period, independent yet similar in nature experiments were performed. In Experiment 1, from October 2013 to February 2014, marandu palisade grass was fertilized with 70 kg.ha-1 of N and 50 kg.ha-1 of P2O5 and cut intervals (7, 14, 28, 56, and 112 days) were evaluated in a randomized complete block design with four replications. In Experiment 2, from November 2014 to March 2015, in addition to the same cut intervals evaluated in Experiment 1, two fertilization conditions were also studied, one of which was low (50 kg.ha-1 of P2O5 and 75 kg.ha-1 of N) and another one that was high (100 kg.ha-1 of P2O5 and 300 kg.ha-1 of N). In Experiment 2, a factorial scheme with two levels of fertilization and five levels of cut intervals was used in a randomized block design with four replications. In Experiment 1, the highest indexes of horizontality (IH) occurred (p<0.05) in the plants under cut intervals of 7, 14 and 28 days, in relation to the plants cut every 56 and 112 days. In Experiment 2, only the plant cut every 7 days showed an increase of IH (from 1.3 to 1.5) (p<0.05) with the improvement of the high fertilization condition. The remaining forage mass increased (p<0.05) with the cut interval, from 412 to 483 g.m-2 and from 412 to 571 g.m-2 in Experiments 1 and 2, respectively. In Experiment 2, there was an increase (p<0.05) in the remaining forage mass (from 447 to 505 g.m-2) and the percentage of live stem (from 23 to 33%) with fertilization at all cut intervals. In both experiments, the highest cut intervals increased (p<0.05) the forage mass removed (from 95 to 840 g.m-2 and from 44.8 to 843 g.m-2 in experiments 1 and 2, respectively) and leaf area index (LAI) removed (from 1.0 to 4.3 and from 0.4 to 3.9 in experiments 1 and 2, respectively). In Experiment 2, the improved fertilization condition resulted in an increase (p<0.05) in the forage mass removed (from 261.3 to 391.8 g.m-2) and LAI removed (from 1.6 to 2.1). In Experiment 2, when the fertilization condition was high, there was (p<0.05) less percentage of live leaf removed in the canopies under intermediate cuts (28 and 56 days). When defoliation is very frequent, the greater availability of nutrients in the soil contributes to the marandu palisade grass to modify its form of growth from upright to prostrate, compared to the condition of less availability of nutrients in the soil. Increasing the cut interval and fertilization improved the forage removal of marandu grass.

摘要 土壤养分有效性的提升，或可在高频刈割条件下更显著地改变饲用植物的生长形态。为验证该假说，本研究针对马兰杜栅状臂形草（*Brachiaria brizantha* cv. Marandu，异名*Urochloa brizantha* cv. Marandu，俗称marandu palisade grass）在不同刈割间隔与施肥处理下的生长形态变化，以及上述变化对刈割后被移除牧草量与残留牧草量的影响进行了表征。
本研究设置两个试验周期开展，各周期内均设置独立但性质相近的试验。
试验1于2013年10月至2014年2月实施，供试材料为施加70 kg·ha⁻¹氮与50 kg·ha⁻¹五氧化二磷的马兰杜栅状臂形草，采用随机完全区组设计，设置5个刈割间隔梯度（7、14、28、56及112天），共4次重复。
试验2于2014年11月至2015年3月实施，除沿用试验1的5个刈割间隔梯度外，额外设置2种施肥处理：低肥组（施加75 kg·ha⁻¹氮与50 kg·ha⁻¹五氧化二磷）与高肥组（施加300 kg·ha⁻¹氮与100 kg·ha⁻¹五氧化二磷）。试验2采用两因素（施肥水平与刈割间隔）随机完全区组设计，共4次重复。
试验1结果显示，刈割间隔为7、14与28天的植株，其水平性指数（IH）显著高于（p<0.05）刈割间隔为56与112天的植株。试验2中，仅刈割间隔为7天的植株，其水平性指数（IH）随高肥处理水平提升从1.3升高至1.5，差异具有统计学意义（p<0.05）。
残留牧草生物量随刈割间隔延长而显著提升（p<0.05），试验1与试验2中分别从412 g·m⁻²升至483 g·m⁻²、从412 g·m⁻²升至571 g·m⁻²。试验2中，在所有刈割间隔下，施肥处理均使残留牧草生物量（从447 g·m⁻²升至505 g·m⁻²）与活茎秆占比（从23%升至33%）显著提升（p<0.05）。
两个试验中，刈割间隔延长均使被移除牧草生物量（试验1与试验2分别从95 g·m⁻²升至840 g·m⁻²、从44.8 g·m⁻²升至843 g·m⁻²）与被移除叶面积指数（LAI）（试验1与试验2分别从1.0升至4.3、从0.4升至3.9）显著提升（p<0.05）。试验2中，高肥处理可使被移除牧草生物量（从261.3 g·m⁻²升至391.8 g·m⁻²）与被移除叶面积指数（LAI）（从1.6升至2.1）显著提升（p<0.05）。试验2中，当施肥水平为高肥时，中等刈割间隔（28与56天）下冠层被移除的活叶占比显著降低（p<0.05）。
当刈割频率极高时，相较于土壤养分有效性较低的条件，土壤养分有效性提升可促使马兰杜栅状臂形草将生长形态从直立型转变为匍匐型。延长刈割间隔与提升施肥水平均可改善马兰杜栅状臂形草的牧草收获量。