Abstract
Poly-γ-glutamic acid (γ-PGA) is proposed as an environmentally friendly super water-absorbable agent and fertilizer synergist. However, the influences of γ-PGA on soil aggregates, crop growth, nutrient uptake, water-fertilizer productivity, and economic benefit are still not well-understood. The objective of this study was therefore to explore the effects of γ-PGA on soil water storage (SWS), water-stable aggregates, aboveground dry matter, nitrogen (N) and phosphorus (P) uptake amount and efficiency, cotton yield, irrigation water productivity (IWP), partial factor productivity (PFP) for fertilizer (N, P, and K), and cost-benefit analysis in desertified soil of Northwest China. A field experiment, which consisted of five γ-PGA application rates (0, 20, 40, 80, and 160 kg ha−1, labeled as CK, P20, P40, P80, and P160), was conducted in the cotton growing seasons of 2015 and 2016. The results showed that γ-PGA application significantly increased the SWS of root zone and decreased water consumption. γ-PGA application significantly enhanced the proportion of soil macro-aggregates and the mean weight diameter (MWD) of water-stable aggregates. Compared with the CK, γ-PGA application significantly improved aboveground dry matter, cotton yield, N and P uptake amount and efficiency, IWP, and PFP for fertilizer (N, P, and K). Moreover, γ-PGA application significantly increased net profit of the farmer compared with the CK. However, water-fertilizer productivity and net profit could not maintain a trend of continuous increase with increasing γ-PGA application rates. According to analyzing the production and net profit functions of γ-PGA application, we found that the highest water-fertilizer productivity and net profit were achieved when γ-PGA application rate was 65 kg ha−1. Therefore, this study suggested that 65 kg ha−1 might be recommended as an appropriate γ-PGA application strategy to deal with water scarcity and improve economic benefit and water-fertilizer productivity in barren desertified soils of Northwest China.
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