Effects Of Different Tillage Methods On Rice Field Quality And Pesticide Dissipation

Guangdong is one of the major agricultural production bases in China.In recent years,inappropriate farming practices have led to the deterioration of soil quality and the increasing agricultural non-point source pollution,all of which had impeded the sustainable development of agriculture in Guangdong.In this thesis,Taishan city was taken as the pilot test site and field experiments were used to study the effects of tillage patterns on soil quality(including soil nutrient elements,organic contents and microbes)and pesticide dissipation.Four tillage methods,including traditional farming(TF),control fertilizer and control pesticide farming(CFCPF),less tillage straw returning(LTSR)and no-tillage straw returning(NTSTR)were set as treatment and fields without farming for years as the control,aiming to provide scientific bases for the development of pesticide application technologies,explore the feasibility and potential to increase rice productivity and reduce agricultural non-point source pollution.1.The differences in paddy field quality under different cultivation(1)Nutrient element.In this paper,the total nitrogen(N)contents of LTSR,NTSTR,CFCPF and TF were 243.72,233.64,225.57 and 222.67 mg/kg,respectively.They were almost 12.69%,8.03%,4.3% and 2.96% higher than the controls.Their total potassium(K)content was 20.09,19.89,20.42 and 20.08 mg/kg,respectively and these were 3.93%,2.9%,5.64% and 14.23% higher than the control.The contents of total phosphorus(P)and available phosphorus in TF methods were 2390.96 mg/kg and 174.28 mg/kg,respectively,which were significantly higher than other tillage methods.The results showed that soil nutrients were significantly different among different tillage methods.(2)Soil biomass.The soil carbon(C)content under the LTSR,NTSTR,and CFCPF was 106.38,47.39 and 73.13 mg/kg,respectively.They were 246.7%,54.5% and 138.4%higher than the control,while the soil biomass carbon content of TF was 20.05 mg/kg,which was 34.6% lower than the control.Soil nitrogen(N)content under LTSR,NTSTR and CFCPF was 42.29,15.82 and 15.54 mg/kg,respectively.They were 347.5%,67.4%,and 64.4% higher than the control.The soil biomass nitrogen content of 7.44 mg/kg under TF,which was 21.3% lower than that of control.The results showed that there were significant differences in soil biomass under different tillage patterns.Among them,LTSR had the highest soil biomass and TF had the lowest soil biomass.(3)Soil organic matter.The soil organic matter content under LTSR,NTSTR,CFCPF and TF was 49.58,48.15,46.53 and 43.13 mg/kg,respectively.The results showed that the soil organic matter content of LTSR was significantly different from TF and there was no significant difference between NTSTR and CFCPF.(4)Soil microbial population diversity.The results showed that,there was little difference between NTSTR and CFCPF.Both of them had good kinship microbial populations with high abundance and uniformity.2.The dissolution and absorption of pesticides under different tillage methods(1)During the soil relaxation period.The degradation half-lives of 60% Butachlor Emulsion in LTSR,NTSTR,CFCPF and TF were 7.07,6.30,7.62 and 6.73 d,respectively.After 28 days,all the degradation rates reached more than 94%.The degradation half-lives of 20% clothianidin suspension were 10.04,9.63,12.60,and 8.45 d,respectively.After 35 days,the degradation rate under CFCPF was 83.71% while the others were over 94%.The degradation half-lives of 75% tricyclazole wettable powder were 20.39,16.50,18.24 and12.84 d,respectively.The results showed that during the soil relaxation period,the degradation of pesticides under TF was faster and that under CFCPF was slower.(2)During the rice growth period.The dissipation half-lives of 60% Butachlor Emulsion,20% clothianidin suspension,and 75% tricyclazole wettable powder on plants under NTSTR were 1.30,0.98,and 2.06 d,respectively.The half-lives of LTSR were 1.27,1.21,and 2.56,respectively,which were faster than those of TF and CFCPF.The dissipation half-lives of 60% Butachlor Emulsion,20% clothianidin suspension,and 75%tricyclazole wettable powder in soil were 1.28,1.23,and 1.00 d,respectively,which were also faster than those of TF and CFCPF.The results showed that pesticides degraded rapidly under NTSTR and LTSR during the rice growth period.In summary,the results of this experiment showed that under the NTSTR and LTSR,the soil fertility was better,the soil microbial diversity was more abundant,and the dissipation of pesticides was faster in the growth period of rice.Therefore,less tillage straw returning and no-tillage straw returning methods would help to reduce agricultural non-point source pollution in Guangdong.