Effect Of Combined Application Of Organic And Inorganic Fertilizer On Soil Microbial Biomass Nitrogen And Nitrogen Cycle

Paddy soil has been recognized for its importance in the retention of active nutrition and the environment protection in the wetland. To study the influence of urea and urea combined with rice straw on the soil microbial biomass carbon, nitrogen (SMBC, SMBN), a flooded pot experiment was carried out with two typical paddy soils which were the reddish clayey soil (R) and the purple alluvial soil (P) and sampled in Dongting Lake floodplain in China. The changes of mineral nitrogen, mineralizable nitrogen,fixed ammonium and organic nitrogen were expounded, these factors related to rice uptake nitrogen and SMBN and the labeled substrate nitrogen distribution were also discussed. The experiment was composed of four treatments: control group (CK), labeled urea group (¹⁵NU), the co-incorporation of rice straw powder and labeled urea group (¹⁵NU-S),and the co-incorporation of labeled rice straw power and urea group (¹⁵NS-U), and the ratio of the urea and rice straw combined groups (URSC) was 3:1 by nitrogen.In the rice pot experiment, the average percentages of SMBC to total organic carbon and SMBN to total nitrogen were 2% ～ 5% in different treatments, respectively. The contents of SMBC, SMBN were the lowest at the booting stage, the native SMBN was the majority part of total SMBN. In reddish clayey soil and in purple alluvial soil, the percentages of microbial assimilating urea nitrogen were 1.76% ～ 8.33% and 1.78% ～ 19.17%, respectively; and the percentages of microbial assimilating straw nitrogen were 1.69% 4.98% and 2.05% - 6.23%, respectively. At the matured stage, the percentages of labeled substrate SMBN in ¹⁵NU and ¹⁵NU-S treatments in purple alluvial soil were lower than those in reddish clayey soil. The assimilation capability of inorganic nitrogen increased in the treatment of URSC, there was no significant difference between SMBN in fertilizers treatmeats.Mineral nitrogen increased when the soils were flooded. The average contents of mineral nitrogen in CK and fertilizer treatments in reddish clayey soil were 35.85 mg ? kg^-1 and 126.8mg ? kg^-1, respectively; and those in purple alluvial soil were 128.7 mg ? kg^-1 and 240.2 mg ? kg^-1, respectively. At the beginning of amending fertilizer, the...