Study On Decomposing Dynamic Of Tumorous Stem Mustard Leaves In Soil And Its Nutrient Effect To Rice

The nutrient release dynamic of tumorous stem mustard leaves in soil, effect of tumorous stem mustard leaves returning to soil on rice yield and soil fertility, as well as the present status of nutrient resource management in rice-tumorous stem mustard rotation system were studied by investigation, pot trial, field experiment and laboratory analysis. The purposes of this study were to provide detailed data for utilizing nutrient resource effectively in Chongqing. The main results were as follows:It showed in investigation that the nitrogen fertilizer was used a little more in tumorous stem mustard in Chongqing and the utilization differences among farmers were so obvious that probably lead to the fertilizer lack or excessiveness. The average amount of nitrogen application was 23.3kg N/666.7m2 with the maximum 37.6kg N/666.7m2 and the minimum 13.8kg N/666.7m2, 60% farmers used the nitrogen fertilizer more than 22kg N/666.7m2 and the nitrogen fertilizer was used more in the beginning of growth stage than later which didn't accord with the nutrient absorption rule of the tumorous stem mustard. The nitrogen fertilizer was usually used two or three times with the ratio of 20:30: 50, but the equitable ratio was 20:70:10. The nutrient equilibrium was lost with nitrogen excessively and potassium scarcely.The average amount of nutrient(contained organic manner) used in tumorous stem mustard was 25.6kg/666.7m²N, 8.5kg/666.7m² P₂O₅ and 9.6kg/666.7m² K₂O, the ratio of N, P₂O₅ and K₂O input was 1: 0.332: 0.375, while the ratio of tumorous stem mustard needed was 1: 0.2-0.4: 1-1.7. Among the total nutrient input, the fertilizer of N, P and K accounted for 91.0%, 65.9% and 15.6% respectively, which showed that the nitrogen was mainly provided by fertilizer and the potassium was provided mostly by organic manner. The potassium fertilizer wasn't used by 50% peasant households and used by others with the amount of 1.5-7kg K₂O/666.7m² and most of 2.5kg K₂O/666.7m².After tumorous stem mustard being harvested, its leaves were turned over to field immediately. No fertilizer was used in rice by 80% of peasant households. If being used, the nitrogen fertilizer application was below 69kg N/ hm². The fertilization experience is still short of being studied at present.The results in field and simulated experiments was that tumorous stem mustard leaves had decomposed with the ratio of 96.2% during 50 days under natural condition in field, which showedthat the tumorous stem mustard leaves turnover to field could do no harm to the rice in next season because it had decomposed completely in two months from harvest to transplanting rice. That the tumorous stem mustard leaves turnover could raise the content of the soil inorganic N appearing the net mineralization during the whole culture stage; Wheat straw and rice straw reduced the content of the soil inorganic N appearing the net regularization; Rape straw showed the net mineralization at the beginning of the culture stage, then showed the net regularization. All of these straw treatments raised the content of olsen-P and effective K in soil, the tumorous stem mustard leaves was the best among of them.In the long-period rice-tumorous stem mustard field, even if no fertilizer was used, the rice could make high yield such as 9.2t/hm2 because of plenty of fertilizer to tumorous stem mustard and tumorous stem mustard leaves turnover. Among equal nutrient of tumorous stem mustard leaves turnover, fertilizer and combination of them treatments the rice grain yield had no marked differences, which showed that the tumorous stem mustard leaves and fertilizer could make the same effect to the soil. The result of the rice yield in pot experiment showed that organic manner used together with fertilizer in poor soil had important effect to provide nutrient continuously in soil and raise the rice yield.The rule that rice absorbed nutrition was adapted to three growing focuses in the whole stage. The absorption to nitrogen took on two peaks, one of them was between two and four weeks after transplantation, the other was between eight and ten weeks. The phosphor and potassium absorption peak appeared between eight and ten weeks after transplantation. The effective N content in tumorous stem mustard treatments changed less and the content of effective N, P and K were all higher than other treatments, while the effective N in fertilizer treatments change more which showed that tumorous stem mustard leaves could provide nutrient continuously and stably according to absorption of rice and satisfy the rice with NPK in later stage, so tumorous stem mustard leaves were natural slow release fertilizer.The absorption and accumulation of rice to nitrogen, phosphor and potassium in fertilizer treatments were more than those in control. The absorption and accumulation and the harvest index of rice to nitrogen, phosphor and potassium in tumorous stem mustard leaves with fertilizer treatments were all more than other equal nutrient treatments. The nitrogen and phosphor that the rice absorbed mostly deposited in grain while potassium mainly did in straw. Simultaneously, along with the fertilizer amount raised, the harvest index of nitrogen, phosphor and potassium decreased and the surplus nutrient absorbed mainly deposited in straw. So it is important to return straw to field for maintaining soil fertility and especially mitigating the shortage of phosphor and potassium in China.