| The Loess Plateau is rich in light and heat resources.And the farmland productivity was limited by drought,water shortage and infertility in this area.The large-scale application of mulching measures has effectively improved soil hydrothermal condition and increased crop yield.But at the same time,a great number of crop straws was removed which reducing the input of carbon sources dominated by organic materials,degrading the soil structure,and affecting the growth of crops.Previous researches have suggested that the improvement effect of straw returning on crop yield and soil quality is affected by soil and climate type.Biochar,an inert material derived by straw carbonization,has the characteristics of high porosity and adsorption.Incorporate biochar to the field has a great potential in improving crop yield,soil structure,and soil quality.Nowadays,there are many researches on the effects of straw-C input on soil structure and C&N content in farmland.But there are few researches on the effects of straw carbon input on soil aggregate structure,soil C and N content in dryland farmland,especially in dryland mulched farmland.Therefore,in this study,a two-factor completely randomized block field experiment was set up in a typical Loess Plateau area in Northwest China（Guyuan,Ningxia）.Straw（S）and biochar（B）were added under two planting methods of double ridges with full mulching and plat planting without mulching,respectively,and non-return field was used as control（N）.Six treatments were formed:film mulching with added straw（MS）,film mulching with added biochar（MB）,film mulching without added（MN）,straw added（S）,biochar added（B）non-mulching without added（N）.The effects of different straw carbon inputs on soil hydrothermal,aggregate characteristics,organic carbon,maize productivity,and economic benefits in mulching farmland were studied.The following main results were obtained from the two consecutive years of field experiment from 2020 to 2021:（1）Film mulching and straw carbon input improved the hydrothermal condition in two experimental years.Mulching treatment increased soil water storage compared with non-mulching treatment.Soil water storage under MB and MS treatment was 2.11%and 0.59%higher than MN treatment,respectively.Mulching reduced the effect of air temperature on the soil temperature,extended the warming time and reduced the diurnal temperature difference.（2）The soil aggregate structure was significantly（P<0.05）improved under mulching and straw/biochar added.Compared with N and MN treatments,macroaggregates contents in each returning treatment was significantly increased by 29.50%and 32.48%respectively.Film mulching could significantly（P<0.05）increase the soil macroaggregates.The content of>0.25mm average macroaggregates during 0-60 cm soil layer under MS and MB increased by 31.15%and 27.99%,respectively,compared with MN.The aggregate geometric mean diameter and mean weight diameter increased by 4.27%and 9.41%under mulching treatments in two experiments years.（3）The soil C and N content were increased under straw and biochar added treatments.Contrast with straw-C input,soil organic carbon,dissolved organic carbon,microbial biomass carbon,aggregates organic carbon,and alkali-hydrolyzed nitrogen were decreased under film mulching treatments.Straw-C input treatments significantly（P<0.05）increase soil organic carbon by 7.61%,and the increasement under biochar returning was 2.56%higher than straw from 2020 to 2021.In addition,the aggregate organic carbon content was positively correlated with the aggregate particle size.Both straw and biochar added treatments significantly（P<0.05）improved soil particle organic carbon（22.8%）,dissolved organic carbon（32.37%）and microbial biomass carbon（41.38%）on average from 2020 to 2021.And biochar added combined with plastic film mulching had a better effect than straw returning.On the other hand,straw-C input improved soil total N and alkali-hydrolyzed N content.Meanwhile,compared with MN,MB treatment could promote the accumulation of 0-60 cm nitrate nitrogen content,but decreased the leaching in 60-200 cm soil layer.（4）The biomass and yield of spring maize were significantly increased under mulching and straw carbon input in two experimental years.Straw input significantly increased aboveground biomass and yield by 12.90%and 12.58%,respectively.In two consecutive growing seasons,mulching and straw carbon input significantly improved farmland water use efficiency.MB significantly improved water use efficiency than MS.Mulching increased the income by increasing grain and straw yield.The net income of MS treatment was 839.1yuan·hm-2 higher than MN treatment in two years.Although biochar added increased grain and straw yields and increased output,but net income was reduced due to the high cost of biochar materials.In conclusion,straw carbon input improved soil moisture condition,soil aggregate structure,soil carbon and nitrogen content,and increased spring maize aboveground biomass,spring maize yield,and farmland economic benefits in dryland mulched farmland.The application of biochar under the condition of mulching film has the most significant effect.It can improve soil aggregate structure and soil fertility while maintaining yield,which is helpful to realize sustainable agricultural development in arid areas. |
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