Influence of urea fertilization and urease inhibitor on the size and activity of the soil microbial biomass under conventional and zero tillage at two sites

Fertilizers are frequently used in agriculture to enhance crop yield and qu ality. Increasingly, microbial and enzyme inhibitors are being used to enha nce the efficiency of fertilizer nitrogen use. The assumption being made is that the impact of these compounds is short-term or localized and thus doe s not adversely impact soil quality. This study investigates the implicatio ns of urea fertilizer with and without urease inhibitor [N-(n-butyl) thioph osphoric triamide, NBPT], conventional and zero tillage systems,and soil ty pes on the soil biological characteristics including N mineralization. Micr oplot studies were conducted in clay loam and fine sandy loam soils in Mani toba. Soil type had a significant effect on the soil organic C but tillage did not have any significant effect. Soil microbial biomass C content range d widely (131-1215 mu g g(-1) soil). The clay loam soil generally tended to contain higher biomass C than the sandy loam soil. The potential soil mine ral N production (N-0) was higher in clay loam soil (92.6 mu g g(-1) soil) than sandy loam soil (40.2 mu g g(-1) soil). Tillage systems, urea and urea se inhibitor application had no significant impact on the soil biomass C, N -0, arylsulfatase or acid and alkaline phosphatase content. At these sites considerable fluctuations occurred in the microbial and biochemical propert ies due to the variation of soil type. In general, these fluctuations were mainly related to soil organic matter and soil moisture content. Tillage sy stem, urea with and without NBPT application did not contribute any notable impact on the soil biological properties reported in this study.