Investigating The Mechinisms Of Four Soil Amendments On Improving Oat Yield And Dryland Soil Productivity

Land degradation seriously affects soil productivity and global food security in arid and semi-arid regions.Soil amendments are increasingly being tested to improve soil health attributes with the potential benefits on crop productivity.However,the scientific comparison of field-scale use of single and repeated application of soil amendments has not been reported.The specific objective of this research was to determine the residual and accumulated effects four to five years after a one-time and annual repeated soil amendments,polyacrylamide?PAM?,potassium polyacrylate?PAM-K?,humic amendment?HA?and bentonite-humic acid?BHA?,application on?i?the dynamic changes in soil quality parameters,and?ii?crop productivity indicators at 4-5 years in a dryland area of Loess Plateau,Inner Mongolia,China.The key findings are as follows:1.With increasing the number of years of PAM and PAM-K application,differences in micro-ecological effect were obsreved at different times for the rain-fed farmland.At a depth of 0-60 cm soil,four years of annual application of PAM?M4?and PAM-K?A4?,the soil moisture increased by an average of 34%by M4 and 27%by A4,compared to the control treatment.We also observed a reduction trend across soil amendments in soil bulk density,by an average of 7%,and soil electrical conductivity by 2%.Specifically,soil electrical conductivity was reduced by 23%for M4 and 30%for A4,respectively.Soil nutrient content?available N,P and K?increased in both M4 and A4.Treatments also increased soil microbial biomass carbon?MBC?,nitrogen?MBN?and phosphorus?MBP?by an average of 32%,70%and 53%in M4,and 24%,47%and 35%in A4,respectively.Interestingly,at the 10-20 cm depth,M4 increased MBN by 99%,while at the 0-10 cm depth,increased MBC and MBP by 31%and by 74%,respectively.In the 20-40 cm soil layer,M4 also increased MBC by 62%,and MBP by 50%.Consequently,the oat plant height,aboveground fresh biomass,aboveground dry biomass and grain yield were 76%,147%,128%and 22%for M4,and 34%,91%,102%,and 19%for A4,respectively higher than for the control treatment.A significant improvement in soil quality attributes was observed with repeated annual application of PAM and PAM-K in plowing layer?0-20 cm?and near the application-layer?20-40 cm?.Our results indicate that PAM application is more appropriate for Huangmian soil,than PAM-K,to improve soil health and increase crop yield in dry farming areas.2.Our data illustrated that multiple years of annual application of PAM significantly increased soil profile water storage,while reduced soil bulk density and electrical conductivity in the top?0-20 cm?and deeper layers?20-60 cm?over that for the control or single PAM application.The improved soil micro-ecological environments led to increased activities of soil enzymes urease?up to 106%?,invertase?94%?and catalase?45%?.These in turn promoted soil nutrient turnover and availability?e.g.,76%higher soil alkaline N?,and crop growth,leading to the improved in grain protein?up to 31%?,protein yield?58%?,grain yield?20%?,WUE?3.67 kg hm-2 mm-1?and partial factor productivity of nitrogen?20%?and economic benefit?36%?,as compared to the control treatment.Taken together,these soil and crop performance indicators suggest that repeated annual PAM application for a minimum of 2-3 years would be an effective strategy to combat drought and foster sustainable oat grain quality in dryland agriculture.3.We found that multiple years of annual HA application improved crop growth,and increased grain protein?up to 25%?,grain yield?18%?,water use efficiency?20%?,partial factor productivity of nitrogen?18%?and economic benefit?20%?over that for the control?no HA?during both wet and dry growing seasons.The improved crop residue associated with higher yields led to a greater increment in soil organic carbon sequestration at 0-20/20-60 cm soil layers,soil water storage,and reduction in soil pH,electrical conductivity and bulk density over that for a single HA application.There was an overall improvement in soil micro-environmental conditions.These in turn promoted an increased activity of the soil enzyme urease?up to 128%?and soil nutrient turnover and availability?e.g.,plant available nitrogen was 57%higher for the repeated HA than for the control?.Our results show for the first time that repeated annual HA application of at least 2 years would be a cost-effective strategy to combat land degradation and nurture sustainable crop production in dryland agriculture under widely varying weather scenarios expected with climate change.4.With increasing rates of one-time BHA application,soil profile water storage displayed a piecewise linear increase plus plateau,whereas soil electrical conductivity,pH and bulk density were all reduced significantly?P<0.05?in the top?0-30 cm?and deeper layers?30-60 cm?.The improved soil environments led to an increased activity of soil enzymes urease,invertase and catalase that respectively reached the peak values of 97%?37% and 32% at the rates of 21 to 24 Mg BHA hm^-2.These in turn promoted soil nutrient turnover,leading to a 40%higher soil available P.Compared with the control treatment,application of BHA at the estimated optimum rate?roughly 24 Mg hm"2?increased grain yield by 20%,protein yield by 62%,water use efficiency by 41%,and partial factor productivity of nitrogen by 20%.5.The greatest improvement of economic benefit rate was observed with application of PAM?477 CNY hm-2?,followed by PAM-K?468 CNY hm2?,HA?453 CNY hm-2?and BHA?67 CNY hm-2?.Taken together,different soil amendments had the long-term and accumulation effect on soil water use,soil organic carbon,nutrient turnover,microbial traits and oat production,but the improvement varied depending on the type of material,application strategies,rainfall amount,crop water use during the growing seasons,and soil layers.According to the linear model,the greatest improvement of economic benefit rate was observed with repeated 5 years of PAM application?M5?;M5 would be a new and effective strategy to combat land degradation,and foster a sustainable soil micro-ecological environment and food production in arid and semi-arid agroecosystem under a changing climate scenario.