Effects of poly-γ-glutamic acid on soil pore structure, maize grain filling, yield and water use efficiency under mulched drip irrigation

Poly-γ-glutamic acid (γ-PGA) is a biodegradable and non-toxic and harmless water retention agent, contributing significantly to in the sustainable development of agriculture. This study focused that investigated effect of γ-PGA on soil pore structure, maize growth, grain filling characteristics, maize yield and water use efficiency under mulched drip irrigation, and the optimal application strategy of γ-PGA. The effect of γ-PGA application rates (0, 40, and 80 kg ha⁻¹) on soil structure was investigated using soil column experiments. Field experiments analyzed the effects of these γ-PGA rates (0, 20, 60 and 80 kg ha⁻¹) on maize growth. The results showed that γ-PGA changed the position and number of soil pores; with the increase of γ-PGA application rate, the number of soil pores increased. The number of soil pores with an equivalent diameter smaller than 300μm increased by 9–14 times, and those with an equivalent diameter larger than 1000μm increased twelvefold. The soil water storage increased by 2∼27 %. γ-PGA prolonged active grain filling period by 1–3 days, increased the maximum grain filling rate (Vmax) by 3∼15 %, the average grain filling rate (Va) by 7∼27 %, and grain weight by 12∼37 %. γ-PGA treatments significantly increased maize plant height, stem diameter, leaf area index (LAI), ear width, grain number per row and 100-grain weight. Compared with P0, yield and water use efficiency for γ-PGA treatment were increased by 4.9∼21.8 % and 1.0∼18.1 %. Based on the Gaussian optimization model and considering local actual conditions, we recommend that the optimal rate of γ-PGA is 70 kg ha⁻¹ in the region. This study provided a theoretical basis for water-saving irrigation of maize under mulched drip irrigation.