Integrated Evaluation On Soil Quality Under Different Tillage Systems In Semi-arid Area Of The Loess Plateau

In 2001,Gansu Agricultural University started a long-term conservation tillage project,funded by Australian Centre for International Agricultural Research,at Lijiabu Village,Dingxi,Gansu Province.The overall aim of the project was to study the effects of conservation tillage on crop productivity and soil quality,the adaptation of conservation tillage in the Loess Plateau where soil is prone to severe erosion,and its underlying mechanisms.The PhD project was part of this long-term project.There were six treatments with two tillage systems and three ground covers,namely conventional tillage (T),no-till without stubble retention(NT),conventional tillage with stubble incorporated (TS),no-till with stubble retention(NTS),conventional tillage with plastic film mulch(TP) and no-till with plastic film mulch(NTP).The experiment was fully-phased with two rotation sequences.Phase 1 started with field pea followed by spring wheat(P→W) whereas phase 2 started with spring wheat followed by field pea(W→P).The objectives of this thesis are:1) to quantitatively analyze effects of soil chemical,physical and biological properties on soil quality and productivity under different tillage systems and the driving factors for the changes of soil quality under tillage in a long-term,2) to select the best soil quality assessment indicators,and 3) to establish soil quality assessment models that are suitable for the erodible environment of semi-arid region on the Loess Plateau.The key results from the study are summarized as follows:1) The study selected 8 most sensitive indicators out of 29 assessment indictors that are used to evaluate soil physical quality,soil fertility,soil health and land productivity in the semi-arid region in the Loess Plateau.These 8 indicators were water stable aggregates,organic matter,total nitrogen,available nitrogen,invertase activities,grain yield,net income,ratio of output and input.The integrated assessment models established using the addition and multiplication method and weighted integrated method for soil quality assessed under different tillage systems,and the results from two assessment systems were similar and highly correlated.This showed that these 8 indicators could provide the best fit for the actual situation in the western Loess Plateau. 2) Soil quality can be improved by NTS.The order of integrated soil quality index(ISQI) from high to low was NTS,TS,NTP,NT,T and TP in P→W rotation,and NTS,TS, NT,NTP,T and TP in W→P rotation.No-tillage and stubble retention,in general,can improve soil structure,reduce soil and water erosion and soil nutrient loss,and hence increase crop productivity.This will,in turn,increase organic material returned back to soil,ensuring the high reproduction and activity of soil organisms.Accordingly,soil biological activity is conducive to improvement of soil structure and soil fertilizer.As a result,the healthy farmland ecosystem is built,thus inducing improved soil quality. Moreover,soil physical quality,fertilizer quality,soil health and integrated soil quality in W→P rotation were higher than that in P→W rotation.On the contrary,Soil productivity in W→P rotation was lower than that in P→W rotation.4) Soil physical quality can be improved by NTS.Soil water,soil structure and water infiltration rather than soil temperature were the dominant indictors for soil physical quality.The order of soil physical quality index(SPQI) from high to low was NTS,NTP, NT,TS,T and TP in P→W rotations,while the order of SPQI was NTS,NTP,TS,NT, TP and T in W→P rotation.This indicated that NTS have the strongest effect on soil physical quality.There is no big difference among different treatments' bulk density and total porosity,but Non-capillary porosity and aggregates under NTS was greatly improved,enhancing soil infiltration and reducing runoff and sediment.Surface soil water content under no-till with stubble retention was greatly improved up to 56% compare to conventional tillage,although there is no big difference among different treatments' water storage at 0-200cm.The average WUE of field pea under NTS cross years was 15.8%,17.3%,10.3%,5.4%and 9.2%higher than that of T,NT,TS,TP,an NTP,respectively.The average WUE of spring wheat under NTS cross years was 0.6% lower than that of TP,and 15.6%,16,7%,12.6%and 0.8%higher than that of T,NT,TS and NTP,respectively.Improved soil structure arised from no-tillage and stubble retention can enhance water infiltration,reduce runoff and increase topsoil water content,hence improve soil physical quality.4) Soil fertilizer quality can be improved by the two stubble retention systems.The balance of soil nutrients determined the direction of soil fertility.The order of soil fertilizer quality index(SFQI) from high to low was:NTS,TS,NTP,NT,T and TP in P→W rotation,and NTS,TS,NT,NTP,TP and T in W→P rotation.In comparison with the baseline soil fertility before experiment started,total and available N and P increased for all the treatments,especially on the NTS and TS treatments.Potassium, however,decreased for all the treatments except for NTS and TS treatments.This indicated that the NTS and TS treatment can replenish the soil nutrient pool via stubble retention or stubble incorporation.Soil nitrogen,phosphor and potassium decreased due to harvesting products.Output of soil potassium removed out of cropland with crop straw,which can be returned back to soil by organic material recycling.The output of soil nitrogen and phosphor is associated with grain seeds,which is removed from crop field forever.Therefore,stubble retention combined with nitrogen and phosphor fertilizer supply can replenish the soil nutrient pool in the loess plateau. Although soil pH value can not be used to directly indicate the level of soil nutrients,it is a useful indicator to indirectly show the soil fertilizer quality by influencing transformation,forms and availability of soil nutrients.On the contrary,the change of pH had an opposite trend to the change of soil nutrients under both rotation sequences. This suggested that although soil pH value can not be used to directly indicate the level of soil nutrients,it is a useful indicator to indirectly show the soil fertilizer quality by influencing transformation,forms and availability of soil nutrients.5) Soil health can be improved by the 3 no-till treatments.Soil catalase and hydrolases activities are the dominant factors to improve soil health.The soil health index(SHI) orders from high to low were:NTS,NTP,NT,TS,TP and T in both rotation sequences. Soil catalase and hydrolases activities in 0-30cm were higher on the no-till treatments (NT,NTS and NTP) than on the cultivation treatments(T,TS and TP) regardless cover or not,covered by stubble or plastic film mulch.This indicated that soil catalase and hydrolases activities are the dominant factors for the 3 no-till treatments(NTS,NTP, NT) to improve soil health.Relatively,microorganism amount is intermediate for the NTS treatment,but soil health index on NTS were higher than those on the other tillage systems.This showed that not all microorganisms but active microbiomass that can help maintain soil nutrient recycling and improve soil health,indicating microorganism amount is an unimportant factor for soil health.6) Soil productivity can be improved by the 3 no-till treatments.Grain yield,benefits and ratio of output and input were the dominant factors of soil productivity.The order of soil productivity index(SPI) from high to low was:NTP,NTS,NT,TP,T and TS in P→W rotation,and NTS,NT,NTP,TP,T,TS and TP in W→P rotation.NTS improved the rotation grain yield significantly while no-till without stubble retention had the worst grain yield compare to conventional tillage system.The average yield of spring wheat under NTS was 18.10%,26.21%,13.15%,2.34%and 2.38%higher than that under T,NT,TS,TP and NTP respectively.The average yield of field pea under NTS was 20.25%,30.33%,15.83%,8.82%and 10.39%higher than that under T,NT,TS, TP and NTP respectively.The average benefits of NT within 3 rotation cycles was 37.52%,194.58%,9.02%,86.79%and 13.99%higher than that of T,TS,NTS,TP and NTP respectively.The average ratio of output and input under NT within 3 rotation cycles was 0.61,1.28,0.52,1.10 and 0.52 times higher than that of T,TS,NTS,TP and NTP respectively.