| Soil erosion with unstable and low precipitation limit the agriculture production on the Loess plateau,China.Therefore,how to improve soil condition and thus crop productivity enhancement of cultivated land is a huge challenge facing in the Loess Plateau.In semi-arid areas,conservation tillage is considered to be a key measure to inhibit soil degradation and improve rainfall utilization.However,long-term single conservation tillage often causes problems such as soil compaction and nutrient stratification,which limit land productivity.Rotational tillage system can alternately use different tillage methods,effectively overcome the disadvantages caused by single tillage method.Soil and land productivity improvement is a long-term and slow process,however,at present,the analysis of rotational tillage study is mostly based on the results of short-term experiments.Rotational tillage systems with different tillage methods combination may showed short-term or gradually accumulated advantages,however,the existing research still lacks the analysis of the long-term in-situ effect of rotational tillage on soil productivity improvement.There are still knowledge gaps of how about long-term rotational tillage on soil improvement?Do they have environmental and ecological advantages?Does the land productivity level rise?All of these are not only basic agricultural production issues,but also extension and innovation of the farming system.They are even a major demand for the implementation of the strategy of small farmers'economy and farmers'precise poverty alleviation in the Loess Plateau.Therefore,based on a long-term residue returned tillage experiment?2007-2019?under the Wheat-Maize rotation system,with the conventional plowing?CC?as the control,We set three fertilization pattern:Common fertilization(N=255 kg·ha-1,P=150 kg·ha-1),regionally recommended balanced fertilization mode(BF:N=150 kg·ha-1,P=120 kg·ha-1,K=90 kg·ha-1),and reduced fertilization mode(DF:N=75 kg·ha-1,P=60 kg·ha-1,K=45 kg·ha-1),and five tillage systems:continuous no tillage?NN?,continuous subsoiling tillage?SS?,no-tillage and subsoiling tillage rotation?NS?,subsoiling tillage and plowing tillage rotation?SC?,plowing tillage and no tillage rotation?CN?.The soil water storage,soil structure improvement,soil main nutrient accumulation and soil productivity improvement were analyzed.In addition,the greenhouse gas emissions of the farmland during the whole wheat and maize cycle were measured from 2017 to 2019.The soil microbial characteristics at wheat harvest in June2018 were subjected to diversity and metagenomic sequencing to further evaluate the environmental effects of long-term in-situ tillage and explore the microbial mechanisms of nutrient enhancement.The results may provide a basis for further development and innovation of the Loess Plateau tillage system.The main findings of this study are as follows:1. With the increase of in-situ time,the effect of tillage on soil moisture gradually strengthened,and the application of NN treatment during the cycle will be beneficial to the soil water storage increasing at the end of the cycle.At Cycle 1,Cycle 2,Cycle 3,NS significantly increased the precipitation conserve rate by 3.4%,7.1%,and 5.0%,during fallow time,compared with CC.With the increase of in-situ time,the soil water conserve rates of CN and NS were significantly higher than CC in Cycle 4,and the storage rates of CN were significantly higher than NS in Cycle 5 and Cycle 6,and the storage was significantly improved compared to CC by 8.6%and 7.4%,respectively.During the critical growth period,the NN observed the highest soil water storage in the initial filling stage under the three fertilization,followed by NS and CN.Analysis of the water use efficiency during the cycle showed that in Cycle 1 and Cycle 2 both of fertilization and tillage significantly affected water use efficiency,and the effect of fertilization was greater than that of tillage.With the increase of in-situ time,the effect of fertilization on water use efficiency gradually weakened,but the effect of tillage on water use efficiency gradually strengthened,In Cycle 5 and Cycle 6,CN showed advantages than others.In Cycle 6,soil water use efficiency of the combination CN and BF is equal to CN and DF,and the absolute value of water use efficiency improved by 1.2%compared with the combination of CF and CC.2. In this study,the contents of macroaggregates in the 0-20cm soil layer under the six tillage methods of the three fertilization methods all gradually increased with the increase of the tillage application,and all showed the effect of improving the soil structure.Under balanced fertilization,the rate of macroaggregates content in NN treated soil increased fastest,and the content of macroaggregates in BF and NN treated soils was the highest,after11 years of tillage application.Compared with the combination of CC and CF,the content of macroaggregates under BF and NN significantly increased by 6.17%,indicating that the application of mechanical tillage in rotation tillage system will show partial destruction of the aggregates.3. The test time had the most significant effect on the soil organic matter content in the0-20 cm soil layer,followed by tillage.With the increase of the test time,the soil organic matter content gradually increased.Under different tillage treatments,after 11 years of continuous tillage,NN had the highest soil organic matter content,followed by SS.Tillage has the most significant effect on soil organic matter content in the 20-40cm soil layer.Under different tillage treatments,after 11 years of test,the CN had the highest soil organic matter content,and increased by 1.21 g·kg-1,0.92 g·kg-1and 0.74 g·kg-1than CC under CF,BF an DF.4. With the increase of the test time,the soil total nitrogen showed a decreasing trend in Cycle1-Cycle 3,and increasing fluctuation in Cycle 3-Cycle 6.The NN observed the highest total nitrogen content in the 0-20 cm soil layer.In the 20-40 cm soil layer,soil total nitrogen content fluctuated weakly.The soil total nitrogen content of NN and SS under DF and CF treatment showed a downward trend with test time.After 11 years of continuous tillage application,CN treatment under DF observed the highest soil total nitrogen content,followed by CN treatment under BF.5. During the whole period of the wheat and maize rotation system,the maximum percentage of carbon emissions from farmland soil was from the fallow period.The rate of soil carbon emissions during fallow period ranged from 5.8 to 6.6 kg C·ha-1·d-1 and carbon emissions ranged from 1680 to 1980 kg C·ha-1.Across all of the tillage methods,NN,NS,CN,and SS treatments significantly reduced soil carbon emissions,in the fallow period,compared with CC.Under different tillage methods,SC observed the highest total carbon emissions,by a significant increase of 84 kg C·ha-1 compared with CC.NS and SC significantly increased N2O emissions during the maize growing season,by 266 kg N·ha-1and 434 kg N·ha-1 than CC,respectively,no differences observed among SS,NN,CN and CC.The calculation of the total GWP during of whole cycle showed that the application of SS,NN,NS,and CN could significantly reduce the GWP value.Among them,NN treatment observed the lowest GWP value,significantly decreased by 2130 kg·CO2·ha-1 than CC.6. Tillage significantly affected the Shannon index of the bacterial community,not the ACE index.At TOP10,tillage had significant effects on Proteobacteria,Acidobacteria,Actinobacteria,Chloroflexi,Gemmatimonadetes,Planctomycetes,and Tectomicrobia.NS significantly increased the abundance of Acidobacteria,Chloroflexi,and Gemmatimonadetes,while decreased the abundance of proteobacteria.Compared with CC,SC significantly increased the abundance of Gemmatimonadetes and Planctomycetes,while decreased the abundance of Proteobacteria and Actinobacteria species.CN and NN significantly increased the abundance of Gemmatimonadetes and Acidobacteria than CC,respectively,while SS significantly decreased Proteobacteria.7. NN treatment significantly increased the genes of Carbon metabolism,Biosynthesis of amino acids and Carbon fixation pathways in prokaryotes than those of CC,while decreased the gene abundance of Glycine,serine and threonine metabolism and Citrate cycle?TCA cycle?.The results showed that in comparison to the CC,no-tillage may increase the carbon metabolism,amino acid biosynthesis,and prokaryotic carbon fixation potential,while may reduce the metabolism of glycine,serine and threonine,and decrease the soil Gene Abundance Related to the Tricarboxylic Acid Cycle.Further analysis of COG species related genes of prokaryote carbon fixation in the KEGG pathway showed that,compared with CC,the prokaryote carbon fixation pathway related species Crenarchaeote?29d5 and Crenarchaeote?76h13 belong to Crenarchaeota Archaeon?MY3,Evergladensis,Gargensis and Viennensis belong to Thaumarchaeota under NN significantly increased,indicating that NN be conducive to improving the soil's ability to fix carbon by the increase of species related to carbon fixation by prokaryotes.Compared with CC treatment,NN treatment significantly decreased the abundance of genes related to the tricarboxylic acid cycle pathway.Further analysis of the gene abundance of each reaction-related enzyme in the tricarboxylic acid cycle pathway showed that tillage significantly affected the gene abundance of malate dehydrogenase?1.1.5.4?and citrate synthase?2.3.3.1?.Among them,NN treatment significantly increased the gene abundance of malate dehydrogenase compared to CC,which may be beneficial to the conversion of malate to oxaloacetate during the tricarboxylic acid cycle.In addition,NN decreased the abundance of citric acid synthase gene compared to CC,which may decrease the reaction rate of the tricarboxylic acid cycle,by decreasing conversion of acetyl-Co A to citric acid,which is the rate limiting enzyme of the tricarboxylic acid cycle.8. In the initial of the experiment,the yield different weakly across all of the treatment,while with the in-situ time increase,the difference of yield under tillage methods became larger.After Cycle 3,the yield of NS and CN increased greatly.The findings showed that with the extension of the in-situ time,the combination of plowing tillage and no tillage rotation and the no tillage and subsoiling tillage rotation significantly improved the level of soil productivity.The CN treatment observed the lowest yield stability index and highest yield sustainability index,indicating that the plowing tillage and no tillage rotation be the more suitable tillage combinations for yield enhancement and stabilizing the loess plateau.In general,long-term single conservation tillage and rotational tillage under straw returning fields showed soil improvement effects.Continuous NN application could efficiently increase soil water storage,at the same time,NS and CN rotation tillage application can effectively improve soil water storage and soil retention during the fallow period.The NN treatment under balanced fertilization observed the fastest soil aggregates increase rate,which may be better for the soil structure restoration.With the increase of the cycle,the soil organic matter and total nitrogen content increased fluctuate.After 11 years,NN observed the soil organic matter and total nitrogen content in the 0-20cm soil layer,while CN and CC significantly increased soil organic matter and total nitrogen content in20-40cm soil layer compared to NN.Compared with CC,application of NN significantly increased prokaryotes carbon-fixing pathway-related species,and decreased tricarboxylic acid cycle-related genes,indicating that the addition of no-tillage will increase soil carbon fixation capacity and decrease carbon emission rate.In addition,the application of SS,NN,NS,and CN can significantly reduce the GWP value.Yield analysis showed that with the extension of the positioning time,the CN rotational treatment can effectively improve the productivity of cultivated land.Therefore,it is recommended that the no-tillage could be the base tillage on the loess plateau,which can be combined with the plowing tillage method to adjust the soil structure and soil nutrient distribution to achieve the purpose of soil and soil productivity improvement. |
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