Studies On Soil Nitrogen Mineralization Of Poplar Plantation In North Jiangsu Province

To understand the influence of successive plantation on the productivity of the poplar plantation and its mechanism, a comparable sequence of plantation stand age (agricultural land as control, 4 year-old, and 10 year-old stand of first poplar generation) and plantation generation stand (agricultural land as control, 4 year-old of first generation, and 4 year-old of second generation) was established in Chenwei forest farm, Sihong county, Jiangsu in 2004 repectively. Based on investigating the growth of height and diameter at breast height (DBH) of poplar and soil nutrients from the various trial plots, and identifying the exist of soil productive decline, we determined the characteristics of nitrogen mineralization of soils from the trial plots by the method of laboratory incubation, and also determined soil mineralization by the method of in situ soil core-ion exchange resin bag (ISC-IERB) in the 4 year-old poplar plantation stands of first generation and second generation respectively. Meanwhile, to explore maintaining long-term soil productivity of poplar plantation, we carried out the trial of tillage and N fertilization in the 4 year-old stand of second generation by the split-plot design, and determined N mineralization and mineralized inorganic N leaching by the method of ISC-IERB. The growth of poplar and N and P concentration and content of leaves were measured after one year of treatment. The results were as below:1. The growth of the second generation plants was not good as the first ones. The mean height of the 4 year-old stand of second generation was 11 percent lower than of the 4 year-old stand of second generation and the mean DBH was 37 percent lower.2. With the successive plantation, the content of nutrition of the soils decline. Total N content of the 4 year-old stand of second generation soil (1.29 g kg^-1) was significantly lower than the gricultural land soil (1.45 g kg^-1). NO₃^-N content of the 4 year-old stand of second generation soil (7.67 mg kg^-1) was significantly lower than the 4 year-old stand of first generation soil (30.93 mg kg^-1). Totle P contents of the 4 year-old stand of first generation soil (0.75 g kg^-1) was significantly lower than the gricultural land soil (0.98 g kg^-1), and significantly higher than the 4 year-old stand of second generation soil (0.41 g kg^-1). NH₄⁺-N content and Olsen-P content of soils had little difference among the generations.3. Soils incubation in lab indicated that N mineralization is weaken with the successive plantation. Both the incubate method of destroyed sample and the incubate method of intermittent filter showed the N mineralization of the 4 year-old stand of second generation soil was lower than the 4 year-old stand of first generation soil .Temperature and water content were...