Influence of Humic Acid on the Effectiveness of NBPT in Different Types of Soils

To improve the performance of the urease inhibitor (UI) N-butyl thiophosphorothioate triamine (NBPT) in various fertilizer applications, we combined the humic acid (HA) from coal and NBPT with urea to preliminarily evaluate the effect of HA on the degradation and effectiveness of NBPT. An incubation experiment was conducted in black soil (Chernozem, FAO) and heilu soil (Calcic Kastanozem, FAO), and the NBPT content, urea-nitrogen (N) transformation, enzyme activity related to N transformation and microbial biomass carbon (MBC) content were measured. The results showed that combining NBPT and HA had opposite effects in different soils. In heilu soil, HA delayed the degradation of NBPT, and urea hydrolysis was delayed by approximately 65 days. In black soil, HA accelerated the degradation of NBPT and increased soil urease activity and the MBC content. We concluded that differences in soil MBC content and pH led to differences in the effect of HA on NBPT and that a rapid increase in microbial carbon content caused by HA in black soils led to a faster rate of NBPT degradation. However, the underlying mechanism must be further investigated. In different soils, we concluded that HA affects the effectiveness of NBPT by changing the half-life of NBPT; moreover, the effectiveness of the formulation should be verified in field experiments.