| As an important biomass resource,straw was often discarded and burned without efficient use,which caused great harm to the environment.Straw returning is an important way to solve the problem of straw burning and discarding.In order to facilitate the subsequent utilization of straw returning,high standing stubble is often remained after crop harvested.The previous research has studied the effects of stubble height on the growth of its after-reap crops.However,few studies focus on the chemical and physical characteristics changes of the high stubble-keeping straw and its impact on the follow-up utilization of straws.The aims of this thesis are(1)to study the nutrient distributions and the heating value changes of the high stubble rice straw during the time remained in the field;(2)to analyze the effects of rainfall precipitation and intensity on mineral nutrients of high stubble rice straw;(3)to analyze the effect of different straw-returning regimes on soil nutrients and soil microbial diversity;and(4)to analyze the impact of different rice straw returning methods on the environment.Field study and stimulating lab test were conducted in this study.High stubble remaining treatment was carried out on the rice straw of Liangyou 262(stubble clipped at 60 cm)which was harvested in mid October 2015 and Nanjing 9108(stubble clipped at 50 cm)which was harvested in early December 2016.Three till treatments were convention tillage and high stubble returning(CTH),no tillage and high stubble remaining(NTH),no tillage and high stubble mulching(NTS).No tillage and low stubble remaining(NTL)treatment was also set as control.The main results of the thesis were as follows:(1)The nutrient contents in the high standing stubble of rice straws showed distinct vertical distribution phenomenon.Besides of potassium,the content of hemi-cellulose,total nitrogen,total phosphorus,calcium and magnesium in the high standing stubble increased from the base to the top;while the content of straw’s lignin and cellulose decreased.At the harvesting season with higher temperature,the moisture content of Liangyou 262 rice straw changed marginally,which was mainly kept between 65%and 70%.In the lower temperature season,the moisture content of straw ranged from 47%to 68%,which was significantly relative to the rainfall.After remaining 35 days,the nutrient content of Liangyou 262 rice straw and Nanjing 9108 rice straw changed obviously.Liangyou 262 rice straw’s hemi-cellulose content decreased by 7.36%,the content of magnesium decreased by 20.09%,the content of calcium decreased by 35.58%,and its ash content decreased by 7.13%.The cellulose content increased by 4.24%,lignin content increased by 23.41%,and its calorific value increased by 1.67%.Liangyou 262 rice straw’s cellulose content increased by 4.24%,lignin content increased by 23.41%,and its calorific value increased by 1.67%.Liangyou 262 rice straw’s content of total nitrogen,total phosphorus and total contents of hemi-cellulose,lignin,and cellulose showed a slightly change.Nanjing 9108 rice straw’s hemi-cellulose content decreased by 9.63%,the content of magnesium decreased by 17.44%,the content of calcium decreased by 19.22%,and its ash content decreased by 5.80%.The cellulose content increased by 4.24%,lignin content increased by 23.41%,and its calorific value increased by 1.67%.Nanjing 9108 rice straw’s cellulose content increased by 4.33%,lignin content increased by 35.42%,and calorific value increased by 0.94%.Nanjing 9108 rice straw’s content of total nitrogen,total phosphorus and total contents of Hemi-cellulose,lignin,and cellulose haven’t change significantly.(2)At the total rainfall of 50 mm,the potassium leaching amount reached 0.3 g kg-1;whereas the content of calcium,magnesium ash had no significant change.Under the same rainfall intensity,rainfall increased and the potassium leaching quantity also increased with the increase of rainfall time.There was no significant difference in total potassium content of high stubble rice straw under different rainfall intensities at the same rainfall.In addition,the lab testing results showed that the content of mineral nutrients decreased with the change of time after spike cutting.Rainfall can accelerate the leaching of potassium,while changes of the content of magnesium,calcium and other mineral elements had little relationship with rainfall.The main reason of the decrease of the mineral nutrient content in the high stubble rice straw would be the nutrient release caused by the self metabolism of rice straw,and the rainfall will accelerate the movement of potassium to the soil.Thus,it is not feasible to reduce the actual utilization value of straw itself as a resource for soil improvement by rainfall.(3)The seed germination time of the after-reap wheat under NTH treatment was earlier,compared with that under three other treatments.The content of available potassium in soil under NTH treatment was 20 mg·kg-1 higher than that under NTL treatment,but less than that under CTH treatment and NTS treatment.The contents of available phosphorus and alkali alkaline nitrogen in soil treated with NTH were lower than those of the other three treatments.Soil microbial diversity index and average well color development in the treatments of NTH were both lower than those under CTH treatment.However,there was no significant difference between treatments of NTL treatment and NTS treatment.(4)Compared with CTH and NTS treatment,NTH treatment can also effectively avoid the emissions of greenhouse gas caused by straw burning,and it can reduce the loss of soil organic carbon content.Compared with CTH and NTS treatment,NTH can not avoid the environmental problems caused by fertilization,but it can greatly reduce the water environment problem caused by the retreating of the farmland.This thesis has been studied systematically the nutrient vertical distribution of rice straw,which has positive influence to recycle straw according to different parts.In the rainy season,remaining high stubble and delayed recovery cannot effectively dry rice straw.The change of main physical and chemical characters of high stubble rice straw was not significant during the month or more remaining in the field,and will not affect the subsequent collection and value of energy utilization.Rainfall would accelerate the transfer of potassium from the straw to the soil,but had little effect on other mineral nutrients.It is not feasible to reduce the ash content of straw and improve the quality of straw fuel by rainfall.In this study,no tillage and high stubble remaining treatment could effectively increase the content of available potassium in soil,but had little influence on soil available phosphorus,alkaline nitrogen,as well as the soil microbial diversity.In addition,it is less potentially harmful to the environment. |
PDF Full Text Request