Effects of long-term rice straw returning on the fertility and productivity of purplish paddy soil

The gross amount of crop straw reached 6.73108 t in China, among which the amount of rice straw account for 23.6%. However, 4560 percent of crop straw were burnt or discarded, which not only wasted organic fertilizer source, but also polluted the environment. Recently, with the development of agriculture, chemical fertilizer was widely applied, but the quantity of barnyard manure and green manure decreased greatly. Straw is an important organic fertilizer source of paddy soil, and straw-returning play a significant role in alleviating the shortage of organic fertilizer input, strengthening nutrient recycle and increasing soil fertility and crop yield. According to our literature reviews, using long-term and systemic location experiment to research effects of straw-returning on soil fertility and crop yield are few. In this paper, we studied the effect of rice straw returned to soil and combinations of rice straw with different chemical fertilizers on fertility and productivity of purple paddy soil according to 8-year location experiment. Meanwhile, K nutrient effects, nutrient recycle and balance in straw were also analyzed to provide a scientific basis for reasonable use and optimum management of straw resource, and sustainable development of productivity of purple paddy soil. The field location experiment in purple paddy soil included 10 treatments: CK, N, NP, NK, NPK, M(rice straw-returning into soil ), MN, MNP, MNK, MNPK, respectively. Three replicates and the area of each plot was 6m2. Rate of fertilization were N 150 kg/ha, P2O5 75kg/ ha, K2O.75 kg/ ha, respectively, among which the P, K and 60% of N as basic dressing and 40%t of N as topdressing. The application rate of straws was 7500 kg/ ha. In later September each year, straws were chopped into 57cm fragments, and incorporated into plow layer, irrigate following. Paddy were transplanted in light of local planting specification. The results showed that single return the rice straw or combination rice straw with chemical fertilizer could maintain, even increase rice productivity and soil fertility. Under above conditions a high sustainable rice yield could be achieved; meanwhile the content of soil organic matter, total N and available P increased, and the balance of soil available K could be maintained. Imbalanced application of N, P, and K chemical fertilizer led to a reduction of rice yield and soil fertility. The Rice straw-returned into soil in the first year increased rice yield of the second year significantly. The 8 years (average) yield of rice straw-returning treatments was 39.5% higher than that of the control, and the straw's production (increasing) effect increased year by year with the time expand of straw-returned into soil. Straw could partly replace chemical K fertilizer because nutrient effects of K brought by straw-returning had same function as that of chemical K fertilizer.