| At present,the methods of straw incorporation in China are mainly straw mulching and straw plowed into soil,which still exist many problems such as the reduction of seed quality and soil moisture,and the competition of nitrogen between soil microbes and crop because of the straw slow decomposition when crop straw is applied into soil,thereby negatively affecting the crop yield.These problems can be affected by straw-incorporation methods,and an appropriate method may solve the problems above.Therefore,the objectives of this study were to select an efficient straw incorporation method to accelerate the decomposition rate of crop straw and promote the growth of winter wheat.To achieve this goal,a 5-year field experiment was carried out in the year of 2011-2016 at the Key Laboratory of Agricultural Soil and Water Engineering in Area sponsored by Ministry of Education(34°18?N,108°04?E;506 m a.s.l),at Northwest A & F University.Summer maize straw was used.There were six treatments: control treatment with no straw returning(CK),long straw returning by covering soil(LM),long straw plowed into soil(LP),powdered straw plowed into soil(SP),long-ammoniated straw plowed into soil(ALP)and powdered-ammoniated straw plowed into soil(ASP).We investigated the effect of different pre-treated straw returning on soil physical,chemical and biological properties,winter wheat growth and yield,and then used factor analysis and cluster analysis to evaluate the soil quality under different treatments.The main conclusions are as follows:(1)The treatment of ammoniated straw(ALP and ASP)significantly reduced the soil bulk density,and significantly increased soil porosity and saturated water content of the topsoil layer(0-10 cm),while the effects of conventional straw returning(LM and LP)on topsoil bulk density,soil porosity and saturated water content was indistinctive in short-term.After 5 years for straw incorporation,compared with the control,straw incorporation significantly reduced the soil bulk density,significantly increased the soil porosity and saturated water content of the 0-20 cm soil layer,in which the effect of the powdered and/or ammoniated straw incorporation on improving the soil bulk density,porosity and saturated water content was better than that of conventional straw incorporation.The different straw incorporation had great influence on soil water holding and release capacity at the low water suction,and the effect of ammoniated straw incorporation on improving soil water retention and water release capacity was better than that of conventional straw incorporation.The effect on the soil water holding and water release capacity at medial water suction decreased gradually between different straw incorporation.Compared with the control,straw incorporation mainly improved the total content of water availability by increasing the water content at low water suction section,in which the effect of the powdered and/or ammoniated straw incorporation on improving total content of water availability was better than that of conventional straw incorporation.The powdered and ammoniated straw incorporation worked best with the total content of water availability,compared with other treatments.(2)Straw incorporation last time and soil depth had great influence on the content of >0.25 mm aggregates and the stability of soil structure.Compared with the control,straw incorporation significantly increased the >0.25 mm mechanical stable and water stable aggregates contents at 0-20 cm soil layer,especially for the water stable aggregates.The effect of ammoniated straw incorporation on increasing >0.25 mm mechanical stable and water stable aggregates at 0-20 cm soil layer was better than that of conventional straw incorporation,while the effect of straw length on >0.25 mm soil aggregates was indistinctive.Conventional straw incorporation improved the stability of mechanical stable aggregates at 0-20 cm soil layer and the stability of water stable aggregates at 0-10 cm soil layer in the short term(2 years),while ammoniated straw incorporation could improve the stability of both mechanical stable and water stable aggregates at 0-20 cm soil layer.Compared with the control,straw incorporation could significantly improve the stability of mechanical stable and water stable aggregates at 0-20 cm soil layer in long-term(5 years)for straw incorporation,and the effect of ammoniated straw incorporation on the stable of soil aggregates was the more significant than that of conventional straw incorporation.(3)The treatment of powdered and/or ammoniated straw accelerated the straw decomposition rate and improved soil respiration,and the powdered-ammoniated straw incorporation worked best compared with other treatments.The straw remaining with the treatment SP was 52.26%,which was significantly decreased by 18.4% and 8.2%,respectively,compared with the LM and LP,and the straw remaining with the treatment ALP was 48.79%,which was significantly decreased by 23.8% and 14.3%,respectively,compared with LM and LP,and the straw remaining with the treatment was 42.17%,which was significantly decreased by 34.1% and 25.9%,respectively,compared with LM and LP.And there was a significant positive correlation between soil respiration and straw decomposition rate during the early growth of winter wheat,but the correlation was not obvious in the late growth of winter wheat.Compared with the control,the straw incorporation improved the SOC and TN contents in the 0-20 cm soil layer.And the SOC content of the ammoniated straw incorporation was lower,the TN content of which was higher than that of the conventional straw incorporation.Compared with the control,straw incorporation increased the MBC,MBN,DOC and DON contents and improved the activity of soil sucrase,urease,catalase and alkaline phosphatase in 0-20 cm soil layer during winter wheat growing stages,and ammoniated straw incorporation worked better than conventional straw.(4)The treatment of ammoniated straw(ALP and ASP)had higher soil water storage of 0~100 cm soil layer at the late growth stage of winter wheat,and had lower total water consumption of winter wheat than that of unammoniated straw plowed into soil(LP and SP).The effect of straw incorporation on crop yield and water use efficiency was affected by year and irrigation.Comparably,the treatment of ammoniated straw was better than conventional straw in improving soil physical,chemistry and biological properties,which provided the suitable environment for the growth of winter wheat,increased the effective panicle number and aboveground biomass of winter wheat effectively,and as a result,improved the grain yield and water use efficiency of winter wheat.The 5-year mean winter wheat yields with ALP and ASP was higher than that of conventional straw incorporation,which was significantly increased 7.9% and 11.6%,respectively,compared with LM and by 5.5% and 9.1%,respectively,compared with LP.The 5-year mean water use efficiency(WUE)with ALP and ASP was significantly increased by 7.5% and 11.4%,respectively,compared with LM,and by 7.1% and 11.0%,respectively,compared with LP.(5)A total of 18 soil indicators were selected,and factor analysis and minimum Euclidean distance method were employed to evaluate the overall soil fertility.Two principal factors can be used to characterize the cumulative is 88.58%,and the order of soil quality was as follows: ASP >ALP >SP >LP >LM >CK,that is,the ammoniated straw incorporation worked better than conventional straw on improving soil quality.Cluster analysis showed that six treatments were divided into four groups,and the soil quality of ALP and ASP was the highest,followed by the conventional straw plowed into soil(LP and SP),straw mulching(LM)and the control treatment(CK),which was consistent with the result of factor analysis.Besides,ammoniated straw incorporation could significantly increased the winter wheat yield,which was consistent with the results of factor analysis and cluster analysis,indicating that it was reliable to evaluate the soil quality under different treatments by factor analysis. |
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