Avoidance of environmental pollution and high forage yield by growing napiergrass

纳皮草对土壤中矿物质的吸收能力强，产量高。因此，可以期望避免畜牧业中粪肥的积累对环境造成污染，并通过粪肥的施用获得较高的饲料产量。为了证明这一预期的实现，并阐明为实现这一预期，在不同肥料投入水平下，以鲜重最高490吨/公顷的水平，比较了甘油三酯和高粱的生长特性。两种牧草的干物质产量均随肥料投入水平的增加而增加。但在高肥料投入量条件下，产量随肥料投入量的增加而增加的速度较慢。在较长的刈割间隔期下，红茅产量增长的减缓比高粱更为严重。由此推断，叶面积指数越高，产量增长越慢。另一方面，随着肥料投入水平的增加，sorgo的根重显著增加，而napiergrass的根重没有增加。根系生长差异的具体机制以及根系生长与增产的关系尚不清楚。两种牧草的土壤中均未发现无机氮的积累，但在最高肥料投入水平下生长的红茅茎中，硝态氮的积累水平高于对牛的危险水平。这似乎是由于产量增长放缓造成的。这种放缓的机制应该在未来澄清。

Napiergrass has high abilities to absorb minerals in the soil and to product high forage yield. Therefore, it can be expected to avoid environmental pollution caused by accumulation of manure in the animal husbandry and to obtain a high forage yield through the application of manure into the napiergrass field. In order to prove the realization of this expect and to clarify the growth characteristics of napiergrass to realize the expect, the growth of napiergrass and sorgo was compared under various levels of manure input with the highest level of 490 ton/ha in fresh weight.The dry matter yields of both grasses were increased by the increment of level of manure input. However, the increase of the yield following the increment of the levelof manure input, got slow under high level of manure input. This slow down of the yield increment was more severe in napiergrass than sorgo and under longer cutting interval in napiergrass. It was inferred that the higher the leaf area index, the slower the yield increment. On the other hand, the root weight of sorgo was significantly increased by the increment of level of manure input and that of napiergrass was not increased. The mechanisms of this specific difference in root growth and the relation of the root growth and the yield increment were not clarified. Although there was not found any accumulatin of inorganic nitrogen in the field of both grasses, the nitrate nitrogen was accumulated to the higher level than the dangerous level for cattles, in the stem of napiergrass grown under the highest level of manure input. This was seemed to be brought about by the slow down of yield increment. The mechanism of this slow down should be clarified in the future.