Research On The Effect Of Irrigation And Straw Returning On Soil Physical&Chemical Properties And The Growth Of Wheat

Straw is abundant in China,but the utilization rate is quite low.A large number of straw is burned every year,which causes various problems such as environmental pollution,traffic accidents and so on.Straw contains nitrogen,phosphorus,potassium and trace elements.It is an important renewable resource.It is of great significance to alleviate the imbalance of nutrient elements and make up for the deficiency of soil fertility.Irrigation is not required generally during the growth of winter wheat in the south of China where rainfall is sufficient to meet the needs of winter wheat's growth.The decomposition of straw is slow under natural conditions,so it usually takes a long time to work.However,raising the soil moisture content in the field can accelerate the decomposition of straw.Therefore,this experiment set up a set of irrigation treatment.When the soil moisture content was lower than 75%of field capacity,irrigation was carried out to raise it to 85%,aimed at accelerating the decomposition and promoting nutrient release.The field plot experiment was carried out in the period from 2015 to 2016.In this experiment,three treatments were carried out including straw returning with irrigation(PG treatment),straw returning without irrigation(PN treatment),and no straw retuning and no irrigation(CK treatment).The effects of irrigation and straw returning on soil physical and chemical properties,growth factors and yield were studied to reveal soil physical characteristics,fertility characteristics and the rhythm of wheat's growth.It provides scientific basis for improving the effect of straw returning to field and improving the yield of wheat.The main results of the study are as follows:(1)Irrigation and straw returning can improve soil physical properties.With the gradual decay of straw to form humus,the soil becomes looser,and its structure improves.Straw returning can reduce volumetric weight effectively.The relationship of the volumetric weight of each growth period is PG<PN<CK.Straw returning has the effect of reducing the ineffective evaporation and preserving moisture.The relationship of the soil evaporation after rain is PG<PN<CK,and relationship of the evaporation inhibition rate is PN<PG The effect of straw returning on soil moisture has a duplicity.The relationship of water content is CK<PG<PN at seedling stage,tillering stage and mature stage.But the relationship of water content is PN<PG<CK at jointing stage and heading stage.(2)Irrigation and straw returning can improve soil fertility effectively.In the process of straw decay,all kinds of nutrients are released into soil.At the same time,there are complex chemical reactions that promoting the release and activation of various nutrients in the soil.The relationships of content of organic matter,available phosphorus and available potassium in wheat's growth period are all CK<PN<PG.Compared with no straw returning,straw returning can improve the nutrient content of soil.But it is not enough to offset the consumption of crop growth.Therefore,straw returning must be combined with the phosphate fertilizer,potash fertilizer.At the seedling stage and tillering stage,the relationship of hydrolysable nitrogen content is PG<PN<CK,and its relationship is CK<PG<PN in the period from regeneration stage to maturity stage.In the early stage of straw returning,hydrolysable nitrogen content will be reduced,so it should be combined with the application of nitrogen fertilizer.In the late stage of the decomposition of straw,the absorbed nitrogen before will be gradually released,having the effect of slow release fertilizer.(3)Irrigation and straw returning are beneficial to the growth of winter wheat and the increase the yield.The relationship of plant height is CK<PG<PN at seedling stage and it becomes CK<PN<PG from tillering stage to maturity stage.The relationship of the dry matter accumulation is CK<PG<PN at seedling stage and tillering stage,and it becomes CK<PN<PG from period of regeneration to period of mature.Due to the accelerated growth of wheat after irrigation,these changes happen.Finally,the actual yield of PG treatment is 6.53%more than that of CK treatment.And the actual yield of PN treatment is 3.13%more than that of CK treatment.The increase of spike number and 1000 grain weight mainly results in the increse of yield.