Immobilization and mineralization of nitrogen and decomposition of straw during incubation of soils mixed with wheat straw and nitrogen fertilizer
Acta Pedologica Sinica 23(2): 97-105
A cinnamon soil and a lime concretion black soil from Huang-Hai-Hai Plain of China and a Palouse silty loam from eastern part of Washington state of U.S.A. were mixed with wheat straw (15N labelled and unlabelled) and nitrogen fertilizer (15N labelled and unlabelled) in different rates and incubated under 20.degree. C and 30.degree. C for 7 weeks to investigate the transformation of fertilizer-N and straw-N. More than 70% even all the mineral N was immobilized in the soils incubated only with straw or low rate of N fertilizer under 20.degree. C or 30.degree. C after 1 week; and immobilization was dominant in the soils during the incubation from 2nd to the week. While less N was immobilized in soils incubated with higher rate of fertilizer after 1 week; and part of the immobilized N was mineralized in the soils incubated under 30.degree. C during the period from 2nd to 7th week. It seems that the immobilization rate of N in the soils decreased with the increase of fertilizer-N added. At the end of incubation, 10-50% of fertilizer-N appeared as mineral-N in the soils with higher rates of N fertilizer. About 50-60% of the fertilizer-N and similar range of straw-N appeared as HCl hydrolyzable N. The immobilization rate decreased with the increase of organic matter and total nitrogen contents of the soils and the raising of incubation temperature.