Effect of Nitrogen Sources on Microbial Biomass Nitrogen under Different Soil Types

Knowledge to increase the microbial biomass nitrogen (MBN) as a bulk of free-living microbes in paddy soil is limited. The potential benefit of these microorganisms was evaluated, in this study, under different nitrogen sources and two paddy soils. The results revealed that pots treated with organic matter recorded the maximum value of the total N uptake and MBN, followed by the Urea treated pots. Pots amended with sludge exhibited a higher microbial N forming ability than those amended with straw compost under both soils. But ammonium concentration in soil increased with straw compost application. Under fresh soil treatment, microbial N uptake rate and proportion of plant nitrogen derived from microbial nitrogen sources () were higher than autoclaved soil. A positive correlation was found between the and the total N in rice shoot in both soils. Finally, we can say that MBN was governed not only by the soil nitrogen content but also by the type of the nitrogen source. The addition of sludge to fresh soil increased total MBN and consequently could be indirectly beneficial to rice production especially in poor soils. Thus, soil microbes contribute to plant growth by serving the available nitrogen during the season.