Effects of fertilizer on alfalfa growth in winter fallow paddy fields and alfalfa green manure on rice yield

The rotation of alfalfa (Medicago sativa) and rice (Oryza sativa) is a new model for alfalfa plantations in southern China and many key technologies need to be studied. The effects of using fertilizer (basal and topical applications) and alfalfa green manure on plant growth and soil nutrient content in the alfalfa-rice rotation system were studied in winter fallow paddy soil. The results showed that nitrogen, phosphorus and potassium (NPK) fertilizer application greatly increased alfalfa growth, with biomass yield increasing by 22.6% and 41.9%, compared with no-fertilizer, when 225 and 450 kg·ha⁻¹ NPK, respectively, were applied basally. The yield increased further when this was combined with a topical application of NPK, reaching 11 198 kg·ha⁻¹ in early May of the following year under a combined basal (450 kg·ha⁻¹ NPK) and topical (450 kg·ha⁻¹ NPK) application treatment. An increase in shoot numbers was one of the main reasons for the increased yield. The increase in total N, available P, and organic matter in soil 0 – 20 cm was significant (P < 0.05) for the combined basal and topical application; the increase in the protein and P content of the alfalfa plants were also significant (P < 0.05), particularly for a combined basal and topical application at 450 kg·ha⁻¹. The increase in K content was significant (P < 0.05) for both the basal and topical application; however, the latter increased the translocation of K from the shoots to leaves to a significant degree (P < 0.05). The increase in rice growth with the application of alfalfa green manure was significant (P < 0.05), with grain yield increasing by 18.2% compared to the treatment of not planted with alfalfa and not fertilized with green manure. The results indicate that an alfalfa-rice rotation is a highly efficient system that can produce a high yield of alfalfa while also increasing rice grain yield and alleviating soil nutrient levels. The alfalfa-rice model provides an effective way to develop alfalfa cultivation in southern China.