Studies on Nitrogen Mineralization of Typical Tobacco-growing Soils

In order to investigate the organic nitrogen mineralization of tobacco-growing soils,six typical tobacco-growing soils: Paddy soil(sampled from Shaoyang),Yellow brown soil from Nanzhang,Yellow soil(sampled from Shaoyang),Yellow brown soil from Lichuan,Red soil(sampled from Nanzhang) and Cinnamon soil(sampled from Yishui),were chosen to measure the nitrogen mineralization by using the Warning incubation method.The soils were waterlogged for 56 days.The results indicated that soil ammonium nitrogen showed a tendency to increase sharply,change gently and then decrease significantly during the incubation period.The soil ammonium nitrogen increased rapidly and soil nitrogen mineralization rate was above zero from 0 to 14 days after incubation(DAI),represented as mineralization of soil nitrogen,and the soil nitrogen mineralization rate of the Paddy soil and the Yellow brown soil from Nanzhang was higher than other soils.The soil ammonium nitrogen content changed gently from 14 DAI to 28 DAI.The soil ammonium nitrogen declined remarkably after 28 DAI,and the soil nitrogen mineralization rate was below zero during this period,represented as immobilization of soil nitrogen.The soil ammonium nitrogen content decreased in the order: Paddy soil Yellow brown soil from Nanzhang Yellow soil Yellow brown soil from Licuan Red soil,Cinnamon soil during the soil nitrogen mineralization period.The Paddy soil remained the highest,while the Red and Cinnamon soil remained the lowest soil ammonium nitrogen content among the six soils during the incubation.This demonstrated that the Paddy soil had higher nitrogen-supply ability,but the Red and Cinnamon soil's was lower.Regression analysis showed that the accumulative nitrogen mineralization amount of 7,14,21 and 28 DAI had significant or very significant correlation with soil organic matter and total nitrogen content,which meant that the soil organic matter and total nitrogen content were available index for evaluating soil nitrogen-supply ability.