Abstract
The anionic polymer γ-polyglutamic acid (γ-PGA) was used to coat urea and slow its dissolution. Three types of slow release urea (SRU) fertilizers (polymer coated urea with pore constriction, polymer coated urea with enzyme inhibitor and polymer coated urea with pore constriction and enzyme inhibitor) were prepared and tested for the N-release rate. After using SRU, the effect on the tomato growth was analyzed. The extracts of SRU were analyzed for NH3/NH4 +-N and NO3 −-N. The N-release rate was used to determine the optimum ratio of ingredients. The results show that the three types of SRU met the dissolution rate standards recommended by the Committee of European Normalization. γ-PGA SRU increased the chlorophyll content of tomato (flowering stage) by an average of 100% compared with that grew in untreated urea. The results from soil analysis (0-60 cm in tomato pots) indicate that the content of NH3/NH4 +-N in SRU-treated pots was 25%–61% higher than that in soil from urea-treated pots during the growing period, while the content of NO3 −-N was nearly 50% lower after the tomato had been harvested. Newly formulated SRU fertilizer increases nitrogen uptake and reduces loss of applied nitrogen. Plant growth is enhanced, a valuable resource is conserved, and the aquatic environment benefits from decreased level of nitrate in agricultural run-off.
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