Abstract:
Objective The aims were to study the changes of soil nutrient content and nutrient uptake and utilization characteristics of rice under different matching ratios of Chinese milk vetch (Astragalus sinicus L.) and nitrogen fertilizer, which could provide a theoretical basis for the rational use of zoysia and chemical nitrogen fertilization in southern rice areas.
Method Under the rice-purslane crop rotation system, the treatments were designated, regular fertilization(CF) as control, and four gradients of purslane tillage (15, 22.5, 30, 37.5 t hm−2) at two levels of N fertilizer (80N%, 60N%), for a total of 9 treatments. During the rice harvesting period, soil pH, organic matter, total nitrogen, available phosphorus, available potassium, uptake of nitrogen, phosphorus and potassium and yield of rice were determined using conventional methods. Correlation analysis of different indicators was performed by partial least squares path model (PLS-PM).
Result The results showed that the soil available phosphorus contents significantly increased by 5.08% - 7.46% and 5.40% - 12.38% at 80% N and 60% N levels when the amounts of Chinese milk vetch was tilled at 22.5 t hm−2 and above, respectively. The soil organic matter and available potassium content was inevitably increased. At the same time, the above-ground P2O5 and K2O uptakes of rice could be significantly increased when the Chinese milk vetch returned amount reached above 22.5 t hm−2 and 30 t hm−2 at both N levels, respectively. Overall both improved phosphorus and potassium fertilizer uptake rates and were able to maintain rice yields without decreasing. Correlation analysis showed that the amount of Chinese milk vetch and the level of nitrogen fertilizer application had a highly significant positive correlation on soil available nutrient content, total nitrogen, aboveground nutrient uptake and rice yield, respectively.
Conclusion The return to soil of Chinese milk vetch could significantly affect the soil organic matter, total nitrogen, available phosphorus, available potassium, above-ground nutrient uptake and yield of rice. The level of nitrogen fertilizer application mainly affected the content of soil total nitrogen and thus the above-ground nutrient uptake and yield of rice. The yield of rice could be maintained when 20% chemical nitrogen fertilizer is reduced after the amount of zoysia tilling is 22.5 t hm−2 or more in this area, and the rice yield could also be kept when 40% chemical nitrogen fertilizer is reduced after the amount of zoysia tilling is 30 t hm−2 or more.