Study On Nutrient Release Characteristics Of Crop Residue And Effect Of Crop Residue Returning On Crop Yield And Soil Fertilty

The nutrient release patterns and effect of crop residue return on crop yield and soil fertility were sudied by combining field experiment with simulation experiment. 3 experiments were conducted in this research: (1) the residue of crop (rape, rice, wheat) which were widely planted in the Middle-Lower Yangtze Area decomposition characteristics and nutrients release were studied by nylon net bags under simulating model of rice cultivation; (2) effect of different amounts of rice straw and rape stalk on physicochemical properties of soil surface solution under waterlogged incubation and soil fertility after incubation were explored; (3) the expriment of effect of crop residue return on crop yield, nutrient balance and soil fertility was carried out in the hilly of Eastern Hubei, which treated by different tillage.The main results were as followed:1. The decomposition characteristic of rice straw, wheat straw and rape stalk were studied by method of nylon net bag. The decomposition rate of crop residue was much faster at the beginning (during 30 d), which appeared that rape stalk decomposed faster than rice straw and wheat straw. After the faster decomposition stage, crop residue kept a steady and slow decomposing rate all the time until the end of experiment, and had no influence among rice straw, wheat straw, and rape stalk. After 124 days, the cumulative decomposition rates of rice straw, wheat straw and rape straw were 49.17%, 52.17% and 49.8% respectively. As for the nutrient release rates, it could be arranged with respect to nutrient release rate in this sequence: K > P > C > N from 3 types of crop residue. The rice straw, wheat straw and rape stalk carbon emission was rapid at the beginning and up to 57.53%, 66.58%, and 52.54% at the end of the experiment. The release of nitrogen from crop residue was fast at the beginning of the 20 days, and then entered a relatively stable stage. The phosphorus released from crop residue was rapid at the beginning of the 6 days, which was up to 50%, then in a relative steady stage. Within the first 12 days, the K release rate accounted for 98%, which was close to its total content. Further study revealed that K release rate of wheat straw, rice straw and rape stalk were 93.90 %, 84.38 %, 83.17 % within 2 h.The proportion of between carbon and nitrogen or carbon and phosphorus declinded after straws returned to the field. The declining rate of rape straw was higher than that of stalk and wheat straws.2. The objective of this research was to determine the effect of rape stalk rates on soil surface solution properties through a simulation experiment. Four rape stalk rates was designed as 0, 100, 200 and 300 g/pot and electrical conductivity (EC), pH, total nitrogen (TN), ammonium nitrogen, nitrate nitrogen, organic nitrogen, total phosphorus (TP), total potassium (TK) were measured during the 116 d experiment. The result showed that EC was increased obviously at the beginning and the peak value appeared at the 8^th day with 823, 919, 1242 and 1531μs/cm for the four treatemts. The pH had a slow decrease trend at the 3 beginning days, and then increased rapidly until 16 days and then kept a relatively stable state. The result showed TN was increased obviously at beginning, and the peak value appeared at the 8^th day with 21.81, 32.41, 39.12, and 41.55 mg/L for the four treatents and TN declined rapidly from 8^th day to 44^th day, but there was no significance for TN among different treatments. After 116 d cultivation, final concentration of TN was 7.87, 12.63, 16.88, 22.53 mg/L for the 4 treatments. The ammonium nitrogen had a similar trend as TN. Nitrate nitrogen was very low under long-term submergence. TP was increased by straw returning. TK was increased obviously at the 1^st day with 7356, 29.33, 64.13, and 109.55 mg/L K for different straw use rates which indicated water TK was increased with straw rates increase, and TK kept a steady level during the whole experiment period. The results revealed that rice straw returned back to field could increase soil surface water EC, TP and TK concentration, and there was positive correlation between straw rate and these itemes, while straw returned had little effect on pH and TN. In terms of the nutrients loss, the period within 30 days after the straw application was a critical time to control N, P, and K loss.3. The objective of this research was to determine the effect of rice straw and its returned rates on soil surface solution properties through a simulation experiment. Four rice straw rates was designed as 0, 100, 200 and 300 g/pot and electrical conductivity (EC), pH, total nitrogen (TN), total phosphorus (TP), total potassium (TK) were measured during the 124 d experiment. The result showed EC was increased obviously at beginning and the peak value appeared at the 36^th day with 960, 1150, 1467 and 1620μs/cm for the four treatmentts. The pH had slow decrease trend at the 3 beginning days, and then increased rapidly until 16 days and then kept a relatively stable state. The result showed each treatment had a high TN concentration at the beginning of the experiment which was caused by urea application, and TN was declined rapidly from 20^th day to 76^th day, but there was no difference for TN among different treatments. TP was increased by straw returning. TK was increased obviously at the 1^st day with 6.87, 36.10, 60.27, and 114.23 mg/L K for different starw use rates which indicated water TK was increased with starw rates increase, and TK kept a steady level during the whole experiment period. The results revealed that rice straw returned back to field could increase soil surface water EC, TP and TK concentration, and there was positive correlation between straw rate and these itemes, while starw returned had little effect on pH and TN. In terms of the nutrients loss, the period within 30 days after the straw application was a critical time to control N, P, K loss.4.The analysis of soil fertility after crop residue simulation experiment, Comparison of soil fertility that showed a similar trend in rice straw and rape stalk. The measurement of returning crop residue into soil can effectively increase the content of total organic matters, and there was proportional to the amount of crop residue. Activities organic carbon increased, while stable organic carbon changed less. There was a close relationship between soil organic matter and soil total nitrogen.The more crop residue was used, the higher was the soil total nitrogen. Crop residue application increased the content of soil available potassium, and there was a positive correlation between soil available K and the amount of crop residue used. Application crop residue had little effect on soil pH, and available P.5. The field experimental results showed that the crop residue reapplication increase the yields of paddy rice and rapeseed significantly. Different tillage methods also influenced crop yield, and conventional cultivation was better than no-tillage. Straw returned to the field enabled to reduce bulk density, increase total porosity, improve soil structure, increase the content of the total organic carbon and organic carbon which easy oxidated, reduce the stability of organic matter, increase the activity of organic matter. The total nitrogen was improved, but the pH, available phosphorus, total phosphorus and total potassium changed little. There was hardly difference with different farming methods.