Nitrogen and Phosphorus Decomposition of Debris from Orchard Grass

Grass residues and decomposition of nitrogen and phosphorus in grassing orchards were studied by using the harvest quadrat method. The residues of the 4 grasses, Chamaecrista rotundifolia,Paspalum natatum, Paspalum wetsfeteinii and Borreria latisolia, were 406.00, 1 582.28, 1 542.62 and 658.07 g, respectively, accounting for 33.8%, 76.1%, 59.4%, and 100.0% of the total, respectively. The half-decomposition time of the grass residues was 5 months for P. natatum, C. rotundifolia and B.latisolia, while 6 months for P.wetsfeteini. The nitrogen storage of the annual losses of the 4 grass residues were 90.86%, 67.76%, 88.45% and 88.33%, respectively, which equated the annual losses of orchard nitrogen of 81.16, 119.02, 219.68 and 58.71 kg穐m-2, respectively. These were far less than 864 kg穐m-2.The phosphorus storage of the annual losses of the 4 grass residues were 84.46%, 80.32%, 90.90% and 87.22%, respectively, which equated the annual losses of orchard phosphorus of 167.69, 534.96, 604.49 and 343.22 kg穐m-2, respectively. These were less than the amount of adsorbable phosphorus in the cultivated soil.