Effect of wheat straw addition with nitrogen application on physical-chemical properties of white paddy soil

Objectives The effects of wheat straw directly returning to paddy soil under different ratios of basal-topdressing of nitrogen (N) applications on soil physical-chemical properties and rice yield were studied to provide a scientific base for fertility improvement of low-yield white paddy soil in Jianghuai hilly lands.

Methods Two factor split field experiments were conducted concussively for four years. Wheat straw returning (3000 kg/hm²) or not was the main factor; N fertilizer was divided into three parts and applied in basal, tillering stage and heading stage 80–0–20, 60–20–20, and 40–30–30. The treatments were coded as N_80–0–20, N_80–0–20 + S, N_60–20–20, N_60–20–20 + S, N_40–30–30 and N_40–30–30 + S. Samples of 0–20 cm topsoil were collected to analyze soil physical-chemical properties, aggregates composition and bulk density. Rice yields were investigated.

Results Compared with no wheat straw returning, wheat straw returning improved soil pH effectively under the three N ratios. Under the N ratio of 40–30–30, the soil pH was significantly increased, from acidic and slightly acidic to slightly acidic and neutral, respectively. The soil organic matter, available P, K contents and CEC were also increased significantly with the returning of wheat straw. The contents of >5 mm and 1–0.25 mm mechanical-stable and water stable aggregates were increased, and micro aggregates (< 0.25 mm) were reduced, which indicated the improvement of soil aggregate quality. Soil bulk density was decreased, and total porosity was increased which showed the adverse physical properties of white soil were improved. Straw addition under the N application ratio of 60–20–20 showed the best effect on the improvement of white soil. Rice grain yields in four experimental sites under three N application ratios were increased by 10.2%–23.4%, 0.8%–5.5%, 4.9%–6.4% and 6.4%–9.6%, with the mean of 16.2%, 3.6%, 5.5% and 8.1%, respectively, the N_60–20–20 + S treatment obtained the highest grain yield.

Conclusions Considering the rice grain yield, soil nutrient contents, aggregate stability, bulk density and porosity, N application ratio of 60–20–20 combined with wheat straw directly returning to field can effectively improve the fertility of low-yield white paddy soil, and increase rice yield in Jianghuai hilly lands under single-rice cropping system in Anhui Province.