Effects of green manure rotation on soil properties and yield and quality of silage maize in saline-alkali soils

Saline-alkali lands are widespread in Datong Basin, Shanxi Province. For years, little manure has been used to improve the saline-alkali soils in the region. The barren soil and harsh ecological environment have resulted in a very low production efficiency of agriculture. Green manure has not only been an important part of modern agriculture, but also been traditionally used in agriculture in China for improvement of soil quality. In order to explore the effects of plantation and incorporation of green manure in saline-alkali soil management, a field experiment was conducted to explore the effects of green manure crops in middle level saline-alkali lands on soil physic-chemical properties, maize silage yield and protein content. Soil water content, pH, EC, nitrogen, available nitrogen, available phosphorus and available potassium were analyzed. Six types of green manure (Vicia villosa Roth., Sesbania cannabina Poir., Melilotus officinalis L., Medicago sativa L., Vicia sativa L. and Lolium perenne L.) were used in the study. Results showed that compared with the control (no green manure plantation), soil water content increased by 1.0%-6.2% during the middle and later growth periods of green manure, whereas soil pH and EC decreased by 0.03-0.43 mS·cm^-1 and 0.12-1.50 mS·cm^-1, respectively. Incorporation of green manure led to the return of 15.6-195.4 kg(N)·hm^-2, 5.3-58.8 kg(P₂O₅)·hm^-2 and 34.5-127.9 kg(K₂O)·hm^-2 to soil. With overturning of green manure, soil organic matter, total nitrogen, alkali-hydrolyzed nitrogen, available phosphorus and available potassium contents in the 0-20 cm soil layer increased by 0.42-1.86 g·kg^-1, 0.05-0.34 g·kg^-1, 0.5-32.3 mg·kg^-1, 0.42-4.65 mg·kg^-1 and 3.8-26.1 mg·kg^-1, respectively. The yield and protein content of silage maize increased by 1 294-19 391 kg·hm^-2 and 0.4-23.9 mg·g^-1, respectively. Compared with L. perenne, V. villosa and M. suaveolens increased soil water content respectively by 1.2%-5.2% and 1.0%-5.0% during the middle and later growth periods, whereas decreased soil pH by 0.06-1.30 and 0.06-1.27 and EC by 0.08-0.51 mS·cm^-1 and 0.08-0.47 mS·cm^-1, respectively. Overturning of V. villosa and M. suaveolens respectively returned 179.8 kg(N)·hm^-2 and 150.3 kg(N)·hm^-2, 40.9 kg(P₂O₅)·hm^-2 and 36.2 kg(P₂O₅)·hm^-2, and 65.0 kg(K₂O)·hm^-2 and 93.4 kg(K₂O)·hm^-2 to the soil. The yield of silage maize increased respectively by 18 097 kg·hm^-2 and 14 903 kg·hm^-2 with overturning of V. villosa and M. suaveolens, and protein content increased respectively by 23.5 mg·g^-1 and 19.2 mg·g^-1, compared with overturning of L. perenne. In general, the cultivation of legume green manures was better than graminaceous green manure (L. perenne) in decreasing soil pH, keeping soil water content, returning N, P₂O₅ and K₂O to soil and enhancing soil organic matter. Among the green manures used, V. villosa was the most effective, followed by M. suaveolens. In short, the approach of "planting and incorporating green manure and then rotation" was applicable in similar saline-alkali soil conditions. The planting and incorporation of green manure economically, effectively and environmentally improved medium saline lands, enhanced soil fertility and returned nutrient to soil.