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Xu Z.,Nanjing University of Technology | Lei P.,Nanjing University of Technology | Feng X.,Nanjing University of Technology | Xu X.,Jiangsu Academy of Agricultural Sciences | And 3 more authors.
Acta Agriculturae Scandinavica Section B: Soil and Plant Science

Given the numerous environmental problems caused by chemical fertilizer overuse, agricultural practices are shifting toward the development of environmentally friendly nitrogen (N) fertilizers. In this study, a pot experiment was conducted to investigate the effect of poly(γ-glutamic acid) (γ-PGA), an effective fertilizer synergist, on rapeseed (Brassica napus cv. Qinyou No. 9) productivity, soil N pools, and soil enzymes. Seven treatments were implemented: T1, a check without urea; T2, a check with urea only; T3, urea mixed with glutamic acid; T4, urea mixed with 3 mg of γ-PGA per kilogram of soil; T5, urea mixed with 10 mg of γ-PGA per kilogram of soil; T6, urea coated with γ-PGA (0.9%, m/m); and T7, urea coated with γ-PGA (3.1%, m/m). The results demonstrated that the application of γ-PGA increased the above-ground fresh weight of rapeseed by 7.57-9.26% and the grain yield per pot by 6.46-10.98% compared with T2. The rapeseed grain yield significantly increased from 15.94 ± 0.55 g pot-1 in T2 to 17.69 ± 0.78 g pot-1 in T7. With the increase in pod numbers and seed numbers per pod, the seed yield was significantly improved after γ-PGA application. Culturable soil microbial count and microbial diversity were increased by γ-PGA application. In addition, the effects of application method of γ-PGA have a more important role on the soil microflora than its amount. The reduced loss of N can be attributed to the capacity of γ-PGA to increase the " turnover pool." More mineral N in the soil was immobilized by clays, soil microbes, and γ-PGA at the early growth stage, and the immobilized N was then released at the later growth stage for plant growth. Moreover, urease activity also increased with γ-PGA application. These findings indicated that the urea coated with γ-PGA could be a better choice for agricultural applications. © 2013 © 2013 Taylor & Francis. Source

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