Effects Of Mulching Methods On Soil Carbon Emission And Plough Layer Environment Of Farmland In Dryland

Mulching is widely used in the production of crops in the Northwest dryland,Plastic film mulching effectively solves the"drought and cold"problem that limits the improvement of crop productivity in arid areas,but the problem of residual film and excessive consumption of soil can not be ignored.The application of traditional full-ground straw mulching has the risk of excessive soil temperature drop or even reduced yield in this area.For this reason,the use of the straw strip mulching method with partial ground mulching can effectively coordinate the contradiction between soil moisture and soil temperature.However,in recent years,the climate warming caused by the greenhouse effect has become a great challenge that people are facing today,but there is still a lack of comprehensive and systematic research on the impact of plastic film mulching and straw strip mulching on dryland carbon emissions.In this study,three main crops（winter wheat,spring wheat and potato）were used in the Northwest dryland,and a field experiment was carried out in the semiarid rainfed area of the Northwest Loess Plateau from 2017 to 2020.Three treatments were set up:plastic film mulching（PFM）,straw strip mulching（SSM）and non-mulching（CK）.The influence of different mulching methods on soil carbon emission and the plough layer environment was studied,and the relationship between soil carbon emissions and the plough layer environment and the formation of yield was analyzed,and this study can provide a theoretical basis for dryland emission reduction.The main results are as follows:（1）Mulching can significantly increase the economic yield（EY）of winter wheat and potato,and the yield increase of PFM was greater that of SSM than CK,while the yield increase effect of mulching on spring wheat varied greatly due to years.The reasons for mulching and yield increase were analyzed from the perspective of yield formation:the spike number was mainly increased on winter wheat,the spike number and grain number could be significantly increased on spring wheat,and the single tuber weight was mainly increased on potato.Good vegetative growth under mulching laid a material production foundation for the improvement of economic yields.（2）Mulching had a significant effect on soil physical properties of farmland in dryland.SSM can significantly increase soil water-filled pore space in the plough layer,but it will reduce the soil temperature and soil bulk density in the plough layer.PFM can also significantly increase soil water-filled pore space in the plough layer,but the effect on the soil temperature and soil bulk density in the plough layer varies by crops.Compared with CK,SSM increased soil water-filled pore space of winter wheat,spring wheat and potato by5.4,4.6 and 2.8 percentage points,respectively,but decreased the soil temperature by 1.5℃,0.9℃and 0.7℃,and decreased the soil bulk density by 0.6%,1.1%and 1.1%（P<0.05）.PFM increased soil water-filled pore space of winter wheat,spring wheat and potato by 3.0,4.4 and 4.9 percentage points,and increased soil temperature of spring wheat and potato by0.7°C and 0.8°C,and increased the soil bulk density of spring wheat and potato by 1.1%and1.4%（P<0.05）,but had no significant effect on soil temperature and soil bulk density varies of winter wheat.Increasing soil water-filled pore space can significantly increase the grain number and grain yield of spring wheat,the tuber number per plant and tuber yield of potato.Soil temperature were negatively correlated with the grain number of winter wheat and spring wheat,and the potato number per plant.Reducing soil bulk density could significantly increase spike number and grain yield of winter wheat.（3）Mulching significantly affected soil organic carbon and activated carbon components in the plough layer of farmland in dryland,but the effects on catalase and sucrase activities in the plough layer varied among crops.Compared with CK,SSM significantly increased the soil organic carbon of winter wheat,spring wheat and potato by13.6%,13.6%and 4.3%,respectively,and significantly increased the content of activated carbon components.For SSM,dissolved organic carbon increased the most in spring wheat and potato,and particulate organic carbon increased the most in winter wheat.The effects of PFM on the soil organic carbon and activated carbon components in the plough layer varied greatly among crops.（4）SSM generally reduced soil carbon emission during the growth period of three crops,while PFM did the opposite.The difference of soil carbon emission between mulching treatments mainly depends on the change of soil heterotrophic carbon emission.Compared with CK,SSM significantly reduced soil heterotrophic respiration carbon emission（Rh）during the growth period of winter wheat,spring wheat and potato,soil carbon emission（Rs）was significantly decreased by 11.6%,11.6%and 6.9%.The effects of SSM on soil autotrophic carbon emission（Ra）varied by crops.PFM significantly increased Rh and Ra during the growth period of winter wheat,spring wheat and potato,and significantly increased Rs by 12.8%,17.1%and 31.3%,respectively.SSM significantly improved the soil carbon emission efficiency（EY/Rs）of different crops compared with CK,while the effect of PFM on soil carbon emission efficiency varied by crops.Mulching significantly increased net primary productivity（NPP）of three crops,and SSM had the highest net carbon sequestration potential（NPP/Rs）among the three crops.In addition,the cropland of the three crops all acted as atmospheric CO₂ sinks,and the carbon sinks of SSM and PFM were greater than CK.（5）The soil respiration flux and soil water-filled pore space of winter wheat,spring wheat and potato fit quadratic regression equation.Mulching improved the explanatory power of soil water-filled pore space on soil respiration flux of winter wheat,but decreased the explanatory power of soil water-filled pore space on soil respiration flux of potato.The soil respiration flux and soil temperature of three crops fit an exponential regression equation.SSM and PFM increased the sensitivity of soil respiration flux to soil temperature in winter wheat,but decreased the sensitivity of soil respiration flux to soil temperature in spring wheat and potato.Soil temperature was the main cause of Rs in winter wheat and spring wheat,but Rs in potato fields are sensitive to changes in soil water,temperature and bulk density.The increase of Rh is the main reason for soil carbon loss of various crops.Soil catalase activity had a significant effect on Rs of spring wheat,soil sucrase activity had a significant effect on Rs of potato,but soil enzyme activity had no significant effect on Rs of winter wheat.（6）The regulatory pathways of Rs by environmental factors in the plough layer vary among crops.Rs of winter wheat was jointly affected by the moisture,temperature,bulk density,readily oxidizable organic carbon,particulate organic carbon and dissolved organic carbon in the plough layer,among which the particulate organic carbon had the greatest influence,with an explanatory degree of 84.8%.Rs of spring wheat was jointly affected by the temperature,catalase activity and sucrase activity in the plough layer,and the temperature in the plough layer had the greatest influence,with an explanatory degree of78.9%.Rs of Potato was jointly affected by the moisture,temperature,catalase activity and organic carbon in the plough layer,and organic carbon had the most obvious effect,with an explanatory degree of 81.0%.Straw strip mulching increased ecosystem carbon sequestration and crop carbon sequestration while decreasing soil carbon emissions and improving carbon emissions efficiency in dryland,and it is a cultivation pattern that is conducive to high-yield and high-efficiency,carbon sequestration and emission reduction in dryland agriculture in Northwest China.