Urea Enhanced with Polyaspartic Acid of a Higher Molecular Weight Significantly Increased Wheat Yield and Nitrogen Use Efficiency

Abstract

Polyaspartic acid (PASP) is widely used in agriculture owing to its role in promoting crop growth and nutrient absorption, and its effects are correlated with its molecular weight. In this study, a field soil column experiment using a 15N tracer was conducted to compare the effects of urea enhanced by PASPs with different molecular weights on wheat yield, nitrogen uptake by wheat, and nitrogen residue in the soil. The results showed that urea enhanced with PASPs (PASPUs) increased the wheat yield by 2.02–9.77% than conventional urea (CU) through enhancing the wheat spike number. PASPUs promoted wheat nitrogen uptake, and urea enhanced with PASPs of high molecular weight (>10 kDa) significantly promoted total nitrogen uptake, fertilizer–N uptake, and soil–N uptake by 9.92%, 4.65%, and 19.62%, respectively, compared with CU. PASPUs reduced fertilizer–N leaching by increasing its residue in the 30–60 cm soil layer and decreasing its amount in the 60–90 cm soil layer. A comprehensive evaluation based on radar charts showed that PASPs of high molecular weight showed a significant improvement in wheat yield and nitrogen–use efficiency, compared with CU and urea enhanced with other molecular weights, and is the most recommended PASP fraction for enhancing nitrogen utilization.