| Crop straws were rich in carbon, nitrogen, phosphorus and potassium and trace elements,which were important source of nutrition in agricultural production. Straw returning can improve the physical and chemical properties, biological characteristics of soil and soil fertility, which can also increase crop yield. Straw returning can partly return the nutrient that crop uptake to the soil,which can alleviate the excessive consumption of nutrients. This experiment focused on the rice production characteristics of Heilongjiang Province, which conducted from 2010 to 2014 in the Xiangfang experimental station of Northeast Agricultural University. In order to study the returning rice residue decomposition regulation and nutrient release characteristics, nylon mesh bag method was used. Plot experiment was used to study the effect of continuous and interval straw returning on soil nutrient and rice yield, pot experiment was used to study the effect of different amount of fertilizer application and straw returning on soil nutrient and rice yield. The results showed:The returning rice straw decomposition rate increased with straw returning time, the decomposition rate was the fastest in the first year, which was fitted by logarithmic equation and its matching effect was significant, equation was y = 8.954ln(x) + 60.92,R2=0.977. The returning straw decomposition rate was 60.92%, 67.13% and 70.76% in the first, second year and third year,respectively. Returning straw decomposition rate required more than nine years to reach 80%. The returning rice straw humification coefficient decreases gradually with straw returning time, and it had small changes after two years, which fitted by logarithmic equation and its matching effect was significant, the equation was y =-0.09ln(x) + 0.390, R2 = 0.977. The returning rice straw humification coefficient was 0.390, 0.330, 0.291 in the first, second and third year, respectively,the decomposing rate was 0.183 in the ninth year.The decomposition rate of cellulose, hemicellulose, lignin in returning straw increased with straw returning time. The decomposition rate was the fastest in the first year, The relationship between decomposition rate of cellulose, hemicellulose and returning years was fitted by equation modeling and its matching effect was significant, equation were y纤= 13.47ln(x) + 59.72,R2 =0.932;y半= 15.34ln(x) + 69.25,R2 = 0.974;the relationship of lignin and returning time was fitted by linear regression, the equation was y木= 30.15 x,R2 = 0.957.The decomposition rate of cellulose,hemicellulose, lignin was 59.72%, 69.25%, 30.15% in the first year, 69.06%, 79.88%, 60.30% in the second year, 74.52%, 86.10%, 86.10% in the third year, respectively. Cellulose decomposition rate needed 7 years to reach more than 90%, and hemicellulose decomposition rate needed 4 yearsto reach more than 90%. The carbon, nitrogen, phosphorus and potassium release rate of returning straw increased with straw returning time, the release rate was the highest in the first year. The relationship between carbon, nitrogen, phosphorus and potassium release rate and returning time was fitted by equation modeling and its matching effect was significant, the equations were y C=10.04ln(x) + 67.52, R2 = 0.964;y N= 13.41ln(x) + 59.52,R2 = 0.898;y P= 14.10ln(x) + 70.61,R2 = 0.995;y K= 15.37ln(x) + 75.82,R2 = 0.921. The carbon, nitrogen, phosphorus and potassium release rate of returning straw was 67.52%, 59.52%, 70.61%, 75.82% in the first year, 74.50%,68.82%, 80.38%, 86.47% in the second year, 84.27%, 81.10%, 93.30%, 91.77% in the fifth year,respectively.NO3--N was mainly available nitrogen in soil solution during rice growth. The inorganic nitrogen in soil solution decreased under rice straw returning, nitrogen fertilizer application can increase inorganic nitrogen in soil. The inorganic nitrogen in soil solution decreased under rice straw returning after 10 days of transplanting, base fertilizer application could increase 17.80 kg/hm2 nitrogen, which can reach the same level under non straw returning; after manuring 21.39kg/hm2 of nitrogen could reach the same level under non straw returning after 30 days of transplanting. The available phosphorus concentration in soil solution was high in the early stage after transplanting, and decreased with the rice growth. The average decrease of available phosphorus concentration was 0.021 mg/L under rice straw returning, while it had the same changing trend in the soil solution. The available phosphorus concentration in soil solution increased with the application of phosphorus fertilizer, the straw returning treatment required multi-application of 14.23 kg/hm2 P2O5 to reach the same level under non straw returning treatment. The available potassium concentration in soil solution was high in the early stage after transplanting, and decreased with the rice growth. The rice straw returning and potassium application could significantly increase the available potassium concentration in soil solution. The relationship between available potassium concentration in soil solution after transplanting 10 days and the amount of straw returning was fitted by exponential equation, the equation was y=5.124e0.067 x, R2=0.966. According to the rice yield was 7.5 t/hm2, the available potassium concentration in soil solution increased 3.35mg/L under rice straw returning, compared to non straw returning treatment, correspond to multi-application of 27.38 kg/hm2 K2 O under non straw returning treatment.The content of organic carbon, nitrogen, phosphorus and potassium in soil significantly increased under rice straw returning. After 6 years continuous straw returning, we found that the relationship between organic carbon, nitrogen, phosphorus and potassium in soil and the straw returning amount was fitted by linear equation,the equations were y C= 0.162 x,R2= 0.910;y N=0.013 x,R2 = 0.835; y P= 0.006 x,R2 = 0.884;y K= 0.282 x,R2 = 0.964.The effect of straw returning on available nitrogen, phosphorous and potassium in soil were not significant. Straw returning could increased yield of rice, while the effect was not significant. Nitrogen and phosphate application should be increased, potassium application should be appropriately reduced understraw returning. |
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