| Northeastern China is the main maize production area.In recent years,the biomass of maize straw has increased continuously with the continuous improvement of maize yield,and the straws are abundant in macronutrient and micronutrient,which are one of the sources important of soil nutrients.Due to the special climate conditions,namely little precipitation and low temperature in spring and winter,and the straw decomposes,which leads to the deterioration of the soil sowing layer environment after straw returning.This is the main problem that it is difficult to implement the straw returning in northeast China.Brown soil is one of the main dryland farming soil types in China,and the area in Liaoning province accounts for 49% of the country's total area.It's crucial to research the efficient utilization of corn straw resource in upland brown soil to the sustainable development in northeast China.In this research,the straw returning methods experiment was carried out for continuous six years from 2014 to 2019,and the regional comparative experiment was set in 2014 and 2015 to research the straw decomposition rate and nutrient release under different straw returning methods(no tillage,rotary tillage,plow tillage)as well as the effect on soil total nutrient content.On the basis of the regional comparative experiment,the positioning experiment of straw returning was set in micro for four consecutive years from 2016 to 2019 to investigate the influence of straw returning methods(mixed,buried,removal)and tillage depth(10,30,50 cm)on straw decomposition,soil structure and function.The main purpose of the study is to provide theoretical basis and technical support for straw returning in upland brown soil in northeast China.The main research results are as follows:Three returning methods including no tillage(NTS),rotary tillage(RTS)and plow tillage(PTS)were set,and the results showed that straw decomposition rates were high at the early phase and slowed down at the later phase under the different straw returning methods,with the order of nutrients release rates in all treatments of K > P > C > N.The mean decomposition rates of straw in both years were 38.8%,78.0% and 65.9% respectively for NTS,RTS and PTS treatments.Nutrients release rates of returned straws under NTS,RTS and PTS treatments were respectively 56.5%,78.8% and 69.4% for C,16.7%,53.5% and 38.8%for N,81.3%,92.5% and 89.8% for P,and 92.0%,99.4% and 98.9% for K.The tendency for straw decomposition and C and N release under NTS treatment fitted well with Logistic function,but those of RTS and PTS treatments fitted Michaelis-Menten function.Moreover,K and P nutrients release of all the three treatments changed according to the Michaelis-Menten functions.Straw returning enhanced organic carbon and total nitrogen contents of the 0-15 cm soil depth for RTS and 15-25 cm soil depth for PTS.Then total soil P content of RTS treatment was significantly higher than that of PTS(P < 0.05).However,therewas no significant difference in total soil P content between RTS and NTS treatments,and in total soil K content for all the treatments.The soil fertility were higher under RTS and PTS than NTS with the variation of straw decomposition and soil nutrient in short term straw returning pattern.The straw decomposition was lower under SMO treatment compared with SMT and SMF treatments at the first straw returning year(2016),but the tendency was reverse at the second(2017)and third(2018)years.The straw decomposition proportion under SBO treatment was higher than SBT and SBF in the three straw returning years.The straw nitrogen release was consistent with straw decomposition,while the straw carbon release decreased with tillage depths increased.The soil organic carbon and total nitrogen were decreased with soil depths increased,while increased with straw returning years.Straw returning significantly increased soil organic carbon and total nitrogen compared with straw removal,and the soil organic carbon,total nitrogen and C/N were increased under different tillage depths with straw returning.The tillage 10 cm treatment significantly increased soil organic carbon and total nitrogen stocks in 0-10 and 10-20 cm soil depth layers,tillage 30 cm treatment significantly increased soil organic carbon and total nitrogen stocks in 20-30 cm soil depth layer and tillage 50 cm treatment significantly increased soil organic carbon and total nitrogen stocks 30-40 and 40-50 cm soil depth layers under straw returning treatments.SBT treatment could significantly increased soil organic carbon and total nitrogen stocks in 0-50 cm soil profile in the three years.The relationships between straw decomposition proportion and soil organic carbon,total nitrogen content were showed the positive linear relationships at0-10 and 10-20 cm soil depths,the parabola relationships at 20-30 cm soil depth,and the negative linear relationships at 30-40,40-50,and 50-60 cm soil depth.The release of carbon and nitrogen from straw during decomposition increased the soil organic carbon and nitrogen,and the tilled layer were enriched with soil organic carbon and nitrogen content or stocks.The soil bulk density were decreased with straw returning years increased,and the difference between straw returning and removal were unobvious at the first returning year(2016),while straw returning significantly decreased soil bulk density at the second and third years compared with straw removal treatments.Soil bulk density and soil compaction were increased with soil depths increased.The soil three-phase ratio were decreased under tillage 50 cm treatment at the first and second returning years,and the results was reversed at the third year.The 0-20 cm soil depth soil temperature and water content were significantly influenced by the environment and showed seasonally.The effect of straw returning and tillage depth on soil temperature was not significant,while the deep tillage increased water infiltration depth.> 0.25 mm water-stable aggregate content in tillage 10 and 30 cm treatments was higher than tillage 50 cm,and it was decreased with soil depth increased,tillage 10 cm treatments increased water-stable aggregate content at each size and the meanweight diameter reached peak at each soil depth under all the straw returning methods.The soil structure was destroyed and soil three-phase ratio was increased,> 0.25 mm water-stable aggregate content decreased,increased the water leaching loss with deep tillage.SMO treatment increased soil organic carbon,total nitrogen,total phosphorus and total potassium significantly in 0-10 cm soil depth layer,SBO treatment increased soil organic carbon,total nitrogen,total phosphorus and total potassium significantly in 10-30 cm soil depth layer.The urease and acid phosphatase activity were increased at 0-10 cm and 10-30 cm soil depth layers under SMO/SBO and SMT/SBT,respectively.The ?-glucosidase and N-acetyl-?-D-glucosidase activity were decreased under SM treatments.The bacterial and fungal abundance were significantly increased at 0-10 and 10-30 cm soil depth layers under SMO and SMT treatments,respectively.The relationships between soil p H and bacterial,fungal abundance were negative and the relationship between Chao1 index in Alpha and soil environment factors was insignificant,while the relationships were discovered between Shannon index and soil acid phosphatase activity,urease activity,p H,available potassium,available phosphorus and total nitrogen content were significant,and the relations in bacterial and fungal were reverse.Fungal microbial composition was more obviously affected by environmental conditions compared with bacterial microbial composition.Comprehensive analysis that soil bulk density and soil compaction were decrease,> 0.25 mm water-stable aggregate content increased which maintained soil organic carbon and nitrogen content,improved soil bacterial and fungal abundance as well as urease and acid phosphatase activity at 10-30 cm soil layer under SBT treatment,which has an obvious positive effect on soil fertility in this paper. |
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