Environmentally friendly urea produced from the association of N-(n-butyl) thiophosphoric triamide with biodegradable polymer coating obtained from a soybean processing byproduct

Abstract

Nitrogen (N) losses in agriculture systems are intense, occurring mainly in the form of ammonia (N–NH3). Strategies to mitigate these losses are indispensable for “clean” agriculture towards circular economy. In this respect, combining urease inhibitors with biodegradable polymer coating in the same fertilizer granule is fundamental for reducing N losses. This is considered an innovative strategy for increasing the efficiency in the use of urea in agriculture worldwide. Therefore, this study aimed to test the effect of urea treated with NBPT (N-(n-butyl) thiophosphoric triamide) at the concentration of 80 mg kg−1 and urea treated with 20 mg kg−1 of NBPT and coated with organic polymer (a soybean byproduct) on the reduction of urease activity and losses of N–NH3 as well as to analyze the effect of pH and soil moisture related to these losses. Two field experiments were conducted simultaneously in the Southeast region of Brazil, in 2018. Conventional urea, urea + NBPT (80 mg kg−1), urea + NBPT (20 mg kg−1) + organic polymer were applied in top-dressing at the rate of 150 kg N ha−1 on maize crop. Soil samples were collected daily from the 1st to 7th day and on the 9th, 12th, 16th, 22nd, and 28th day after the application of the treatments for simultaneous determination of: urease activity, moisture, pH, organic carbon, and the quantification of N–NH3. In Experiment I, urea + NBPT (80 mg kg−1) and urea + NBPT (20 mg kg−1) + organic polymer caused reductions in urease activity and N–NH3 losses when compared with conventional urea. However, this effect occurred only in the first few days after the application of the fertilizers. In Experiment II, urease activity was not affected by the treatments. Nevertheless, there was less loss of N–NH3 in the treatments with urea + NBPT and urea + NBPT + organic polymer. Losses of N–NH3 do not depend only on hydrolysis of urea by urease, but they intensify with an increase in soil moisture coupled to high temperatures. Under tropical conditions, soil moisture has a greater effect than pH on losses of N–NH3. The effect of the inhibitor and the organic polymer on the mitigation of N–NH3 losses occurred up to the 7th day after the application of the fertilizer. The reduction of N–NH3 losses of urea with 20 mg kg1 of NBPT coated with the organic polymer were similar to the losses in treatment using urea treated with 80 mg kg−1 of NBPT.