Study On Fixed Ammonium In Soils And Effect Factors On It

Fixed ammonium, an important nitrogen type, plays a remarkable role in soil nitrogen cycle. This dissertation reports the relationships between fixed ammonium and the particle composition, residual organic matter, Kjeldhl nitrogen. We study the feasibility and fine condition of using the Low Temperature Heating Method to determine fixed ammonium in soils, discuss the reason of occurring error. We also study the fixed ammonium in soils sampled west China and effecting factors on it. The results are shown as follows:1. There was correlation between fixed ammonium and particle composition. The contribution to fixed ammonium not only depended on particle size, but also the contents of particles.In soil particles, the content of silt was the highest, followed by sand and clay, according to USSR system and two China systems. Correlation analysis was used to study the relationships between fixed ammonium and particle composition. Results showed that smaller particles were positive correlated with fixed ammonium, but larger particles were negative. In 1978 classification system of China, the particles from fine silt to fine clay were positive related with fixed ammonium. In 1982 classification system, the correlation coefficients between mid silt, fine silt, coarse clay and fixed ammonium were significant or more significant prominence, among of them, 0.01~0.005mm particle was highest. In the combination of particles, no matter what classification system was, almost full combination of particles were correlated with fixed ammonium, accept for fine silt + clay in 1982 China system. However, fine clay and clay was not related significantly with fixed ammonium. The reason was that the analysis result was affected by abnormal data. Fixed ammonium was not only significantly correlated with clay, but also with fine clay, after deleted tow abnormal data.The correlation analysis is an indirect method. The direct method is to determine the contents of fixed ammonium in sand, silt and clay. The results showed that the contents of fixed ammonium in clay was the highest (250 mg Kg-1), followed by silt (163 mg Kg-1) and sand (66 mg Kg-1), accounted for 52.2%, 34.0%, and 13.8% of the sum of three, separately. Furthermore, it was proved that there was no difference between the content determined in 11 soils and the data calculated, that is, the sum of multiplying content of particles by the contents of fixed ammonium.2. There was the difference of relationships between the particle and fixed ammonium in soils from south and north China.The particle components and the contents of the fixed ammonium of 23 soils sampled from north and 12 soils from south China were determined, and the contentsof fixed ammonium in variant particles from 11 typical soils were analyzed. Correlation analysis was used to study the relationships between the fixed ammonium and different particles. The results showed that the content of silt hi north was the highest followed by sand and clay, while the content of sand in south was the highest. The content of fixed ammonium (194 mg Kg-1) in north was larger than that in south (88 mg Kg-1). The content of fixed ammonium in soils from north were related significantly with the content of clay, fine clay, coarse clay, physic clay, and fine silt + clay. The correlation between fixed ammonium and clay, fine clay, coarse clay, fine silt + clay, mid silt + fine silt, and physic clay in south changed from no prominence to a significant level after two abnormal data were deleted. The contents of fixed ammonium in clay from south or north soils were the highest followed by silt and sand, it was proved that there was no difference between the content determined in 11 soils and the data calculated, that is, the sum of multiplying content of particles by the contents of fixed ammonium.3. Whether the Kjeldahl nitrogen method recovers quantitatively the fixed ammonium in soils depended on the clay minerals.The contents of the Kjeldahl nitrgen, the residual fixed ammonium and the fixed ammonium in so...