Studies On Soil Nitrogen Mineralization And Influenced Factors In Plantations

In order to explore the fertility degradation in the different successive rotations of poplar plantations, the poplar plantations with the different ages and different rotations (the first rotation of seven-year-old, the first rotation of eleven-year-old, the second rotation of six-year-old, the second rotation of nine-year-old and farmland) were selected in Sihong County, Suqian City, Jiangsu province in this paper. The research adopts in situ soil core-ion exchange resin bag (ISC-IERB) and laboratory training methods to study soil nitrogen mineralization and influence factors, based on investigating the growth of poplar we determined the relationship between fertility degradation and soil nitrogen mineralization. For further understanding the mechanism of fertility degradation of poplar plantation, we should strengthen the poplar forest soil fertility technical measures to prevent the soil fertility declination. The main results were showed as follow:1. The average height and diameter in breast height of the second rotation plants were not good as the first rotation plants. The average height and the diameter in breast height in the second rotation of six-year-old was 14% and 30% lower than that in the first rotation of seven-year-old, respectively. And similarly, the average height and the diameter in breast height in the second rotation of nine-year-old was 10% and 28% lower than that in the first rotation of eleven-year-old respectively.2. Studies show that the mineralization rate of poplar plantation soils was obviously decreased with the increase of poplar plantation ages, as the first rotation of seven-year-old> the first rotation of eleven-year-old, the second rotation of six-year-old> the second rotation of nine-year-old.3. Studies show that the mineralization rate of poplar plantation soils was obviously decreased with the increase of poplar plantation generations, as the first rotation of seven-year-old> the second rotation of six-year-old, the first rotation of eleven-year-old> the second rotation of nine-year-old.4. The ammonification content and nitrification content of a year in different plantations was the first rotation> the second rotation.5. The seasonal changes of the ammonification rate and the nitrification rate were obviously. The maximum value of the ammonification rate(0.902mg/kg.d) was in the period of August 20th to October 20th, and the minimum value of the ammonification rate(0.126 mg/kg.d) in the period of March 20th to April 20th; The maximum value of the nitrification rate(0.655mg/kg.d) was in the period of June 20th to August 20th, the minimum value of the nitrification rate(0.044 mg/kg.d) in the period of January 20th to March 20th. 6. In the different temperature incubation in the Lab, of soils, the soil mineralized N for all poplar plantations were as the greatest at 15℃, and both the ammonification rate and the nitrification rate were the largest at 15℃. The mineralized N and the ammonification rate as well as the nitrification rate were the greastest in the the condition of 50% field capacity, and obviously higher than that in the conditions of 100% field capacity and 150% field capacity.