Avoidance of environmental pollution and high forage yield by growing napiergrass

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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.