| In this paper,the effects of agricultural waste returning to field on crop growth,yield and soil nutrients were studied by field plot experiment.The changes of nutrients in the process of agricultural waste composting and the effects of crop straw returning to field on water environment of farmland drainage system were also discussed.There were four treatments in the experiment:mushroom residue returning(a),sawdust returning(b)and corn straw crushing returning(c).Three different levels of agricultural waste returning were set for each treatment.The waste mushroom residue was returned to the field according to 3900kg/mu(L),7400kg/mu(m)and 17000kg/mu(H);1 700 kg/mu(L),2 250 kg/mu(m)and 4 400 kg/mu(H)sawdust were returned to the field;Corn stalks were crushed and returned to field at 2500kg/mu(L),5800kgl mu(m)and 11800kg/mu(H),and CK was not treated.Based on the analysis and comparison of crop growth index,yield,soil nutrient content and nutrient changes in the process of composting,the best amount of returning crop straw to field was determined,and the amount of pollutants produced by returning crop straw to field was estimated,so as to provide theoretical basis for rational utilization of agricultural waste,scientific returning to field and protection of water environment in Ningxia Yellow River irrigation area.The results are as follows(1)The results showed that different amount of mushroom residue returned to the field could promote the growth of Chinese cabbage and celery significantly.Compared with the control group,the growth indexes of Chinese cabbage in high-dose returning group increased by 20.8%,12.5%,16.4%,26.6%,26.3%and 35.9%respectively.The reason may be that sawdust is a kind of wood,which has a slow decomposition rate in the soil and absorbs a lot of water in the soil,affecting the growth of crops.Compared with the control group,the growth indexes of Pakchoi increased by 15.7%,37.5%,11.5%,39.4%,15.1%and 19.9%,respectively.(2)During the whole growth process of celery,the growth indexes of celery with high amount of mushroom residue returned to field were lower,medium amount and control increased significantly.Compared with the control group,the increase rates were 30.8%,12.3%,31.8%,21.3%and 16.2%at 90d;When celery was planted for 90 days,the growth indexes of celery were significantly higher than those of the control group,increased by 10.0%,7.9%,9.1%,3.4%,6.5%compared with the control group.The growth indexes of celery were significantly higher than those of the control group,increased by 27.6%,9.9%,26.6%,9.0%,6.0%compared with the control group.(3)The yield of celery returned to field with high amount of mushroom residue was the highest,reaching 6193.8kg/mu,986.1kg/mu higher than that of the control,and the yield increase rate was 18.9%.The yield of celery returned to field with medium amount was the second,reaching 6080.9kg/mu,and the yield increase rate was 16.8%;The results showed that different amount of sawdust returning had different effects on the yield of celery.When the amount of sawdust returning was low,the yield of celery was the largest,reaching 5742.0kg per mu,with an increase rate of 10.3%.When the amount of sawdust returning was medium,the yield of celery was the second,reaching 5634.6kg per mu,with an increase rate of 8.2%;The yield of celery reached 6142.9kg per mu,which was 935.2kg/mu higher than that of the control,and the yield increase rate was 18.0%.When the amount of straw was high,the yield of celery took the second place,and reached 6069.6kg/mu.(4)The contents of soil organic matter,total nitrogen,total phosphorus and total potassium increased by 72.4%,35.8%,43.3%and 25.2%respectively compared with the control group,followed by the medium amount,and the soil nutrient content increased with the increase of the amount of mushroom residue;The results showed that the effect of sawdust returning on soil nutrients was small,and the increase of soil nutrients was larger when the medium and low amount of sawdust returning were 12.1%,13.6%,13.7%,12.5%and 4.7%,7.4%,14.4%,11.3%higher than the control group,respectively;Compared with the control group,the soil nutrient content increased by 14.2%,32.9%,27.8%,19.5%and 7.0%,25.0%,23.5%,17.5%respectively.(5)In the process of agricultural waste composting,the temperature of the compost increased rapidly,and reached the high temperature stage in three days.On the sixth day,the highest temperature was 68℃.The high temperature stage lasted for 19 days,and entered the maturity stage.The color of the compost became darker,and the composting effect was good,which met the harmless standard of composting in China.During the whole composting process,the content of organic matter decreased by 12.6%at the end of composting;The total nitrogen content decreased at first and then increased.The total nitrogen content decreased to the minimum of 2.0%at 7 days;Compared with the initial value,the total phosphorus increased by 0.5%;The total potassium content increased at first and then decreased,slightly lower than the initial value.(6)According to the estimation of the amount of water pollution sources in sierzhigou,the total nitrogen and total phosphorus produced by straw returning were different,and with the increase of straw returning,the pollutant load increased.Under the conditions of high,medium and low straw returning,the total nitrogen production was 1910.5t,939.1t and 404.8t,and the total phosphorus production was 7.6t,3.7t and 1.6T respectively.Through the comprehensive analysis and comparison of experiments,it is concluded that bacterial residue and straw can partly replace chemical fertilizer and can be used for returning to the field.Sawdust should be pretreated before returning to the field to release nutrients in the soil quickly.Different amounts of straw returning to the field will produce total nitrogen,total phosphorus and other pollutants.These pollutants enter the river in the form of rainfall runoff and farmland drainage in the irrigation area,The water quality of the river is decreased. |
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