| Nitrogen(N) is one of the elements required in large proportion for normal growth and development of a plant, and the most mineral element sucked from soil for plants, which has been widely applied for the wood production. Nowadays the use efficiency of N fertilizer(NUE) in our country is low, ranging from 30% to 35%, leading to severe economic harm and environment deterioration. Therefore, scientific and reasonable management measures, optimal fertilization and increasing the recovery of fertilizer are of great significance. Phyllostachys edulis is an important ecological economical bamboo species in our country, accounting for 0.443 million of hectares. The soil natural fertility and productivity of bamboo forest decrease with management period, which could be better solved by using N fertilizer. But, overusing N fertilizer has caused a series of environmental problems. Therefore, improving NUE is a key problem in intensive farming. 15 N tracer technique could distinguish resources of N efficiently, and has been widely used for the research of distribution of N and NUE. In this research, the distribution of N, NUE and soil N dynamics were studied based on typical moso bamboo forest with intensive management using 15 N tracer technique, and the main results were as follows:(1) The ratio of N derived from N fertilizer to total N(Ndff%) of bamboo was different between different ages: 1 a(5.32%-11.96%)>3 a(3.46%-9.18%)>5 a(2.77%-9.18%). Root, underground trunk and leaf had higher Ndff% in young bamboo;rhizome, root and underground trunk had higher Ndff% in old bamboo. The leaf of young bamboo has higher Ndff% than branch, but leaf in old bamboo was lower, later higher than branch.(2) The distribution of N derived from fertilizer was different in bamboo of different ages : 1 a >3 a >5 a, with the distribution being 16.56±1.73 g、8.27±0.83 g and 7.99±0.90 g in single bamboo and distribution ratio being 43.39%,19.96% and 19.22% in forest. The trunk, underground trunk and leaf had higher distribution ratio in bamboo of 1 a, trunk, rhizome and underground turnk had higher distribution ratio in bamboo of 3 a and 5 a.(3) The NUE was different in bamboo of different ages: 1 a >3 a >5 a, with the figure being 3.15%±0.14%、1.58%±0.10% and 1.52%±0.12% on single level, 6.06%±0.27%、2.79%±0.18% and 2.68%±0.41% on forest level. The trunk, underground trunk and leaf had higher NUE in bamboo of age of 1 a. Trunk, underground trunk and rhizome had higher NUE in bamboo of ages of 3 a and 5 a. Trunk, root and rhizome had higher NUE in the whole forest whose NUE was 13.96%±0.88%. The NUE of leaf of young banmboo had a decreasing trend.(4) Under unfertilization management, soil total N(TN), alkali-hydrolyzale N, ammonium N, nitrate N and microbial biomass N(MBN) had higher value in July, total soluble N(TSN), soluble organic N(SON) and SON/TSN had higher value in October. They all had higher value in July after fertilization except for SON/TSN. Between different soil layers, TN, alkali-hydrolyzable N, nitrate N, SON and TSN had higher value in soil layer of 0-20 cm, ammonium N and SON/TSN had higher value in soil layer of 0-20 cm in July, 20-40 cm in October. After fertilization, they all had higher value in soil layer of 0-20 cm except for nitrate N.(5) The residue ratio of N fertilizer in soil decreased with increasing soil layer and time and the value was 28.92%±1.98% for 0-20 cm soil layer and 11.96%±0.70% for 20-40 cm soil layer after growing season. The amount of residual N fertilizer in 0-40 cm soil layer was 85.86 kg N·hm-2 and the amount of loss was 94.81 kg N·hm-2 with loss ratio being 45.15%.(6) NUE could be promoted efficiently by adjusting the stucture of forest stand and rational application of fertilizer, including cutting the old bamboo and retaining the young, combined application of organic and inorganic manure, reducing fertilizer application appropriately and applying N fertilizer shallowly. |
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