Effects Of Structural Variation On Wheat Productivity And Soil Quality And Its Mechanism Under Ridge-furrow Mulching Farming System In Semiarid East African Plateau

The ridge-furrow with mulching system?RFM?has a significant effect on improving crop productivity in semi-arid area.But crop productivity has affected by the changing of the RFM system structural factors,including the ridge-furrow size,mulching material,mulching pattern,planting density and soil nutrients.The coupling relationship between productivity and the structure of RFM system is a hot spot in agroecology.It involves the basic scientific issues to adopt land management and large-scale application for farmers in RFM system,which has not yet been reported,especially in semi-arid rainfed region of eastren Africa Plateau?EAP?.In this study,field experiment with four growing seasons was conducted in Juja,a typical semiarid site of Kenya from 2015 to 2017.It comprises four relatively independent but closely related field experiments:1)wheat productivity respond mechanisms,soil hydrothermal regulative mechanisms and soil quantity under different mulching materials and mulching patterns;2)allometric relationship and yield formation in response to planting density under ridge-furrow plastic mulching in rainfed wheat;3)wheat productivity responses and hydrothermal regulative mechanisms under different ridge-furrow sizes;4)the effects of nitrogen and phosphorus addition on wheat productivity and soil quality under ridge-furrow with mulching plastic.The objectives of this study are to evaluate the quantitative relationship between wheat productivity,water use efficiency and soil physicochemical properties with RFM system structural changes.The main conclusion is as follows:1.Wheat productivity and soil hydrothermal status under different mulching materials and mulching patterns.The experiment was a randomized block design with three replicates for each treatment.Mulching treatments included as follows:1)furrows mulched with wheat straw and ridges mulched with black plastic film?RFbS?,2)furrows mulched with wheat straw and ridges mulched with transparent plastic film?RFtS?,3)furrows unmulched and ridges mulched with black plastic film?RFB?,4)furrows unmulched and ridges mulched with transparent plastic film?RFW?and 5)furrows and ridges both mulched with wheat straw?RFS?.No mulching in RF was used as control group?CK?.The results showed that yield under RFbS,RFtS,RFb,RFt and RFS increased by 79-125.4%,75.1-133.7%,59.3-86.3%,46.3-93.6%and35.4-44.1%,compared with CK in the four growing seasons,respectively.Water use efficiency increased by 125.7-163.2%,118.6-170.2%,71.6-105.3%,60.5-110.5%and 37-54.4%,respectively.Compared with CK,RFbS,RFtS,RFb,RFt and RFS significantly increased soil water storage during the four growing seasons.The order of soil temperature was first RFt,next RFtS,then RFb,RFbS,RF and RFS.Compared with CK,plastic mulching increased soil temperature under white plastic mulching more than black plastic mulching,and mulching straw decreased soil temperature.Among all the ridge-furrow with mulching systems,RFbS and RFtS had the greatest potential for increasing wheat yield and water use efficiency,improved soil water and temperature conditions,and eventually increased wheat productivity and economic benefits.2.Effects of soil quality on different mulching materials and mulching patterns.Compared with CK,RFbS,RFtS and RFS increased significantly soil organic carbon?SOC?and total nitrogen?STN?content,but RFb and RFt significantly reduced SOC and STN.Soil C:N ratio under RFbS and RFtS significantly decreased than that under RFb and RFt.NO₃^--N and NH₄⁺-N contents under RFbS and RFtS significantly increased than those under other treatments.Compared with CK,RFbS,RFtS and RFS significantly increased soil pH and reduced soil bulk density.RFtS and RFbS significantly enhanced soil nutrients,improved soil quality and structure,increased soil organic carbon content,and effectively alleviated soil degradation.3.Density-dependent yield formation and allometric relationships under ridge and furrow with mulching.We conducted a density-dependent yield-formation experiment in field-grown wheat with flat planting?CK?and ridge-furrow with plastic-film mulch?RFM?.Planting densities set as 60,140,220,300,380 and 460 kg ha^-1 seed rates.We found that increased wheat population density(60,140,220,300,380 and 460 kg ha^-1)tended to lower the reproductive allocation and efficiency of conversion of vegetative biomass into reproductive biomass at individual level.Yet at population level,the maximum reproductive output was observed at a medium density(300-380 kg ha^-1),while it was not beneficial to individual survival and reproduction.The principal component analyses?PCA?showed that there were good individual and population performance at 220 kg ha^-1.While the harvestable yield of wheat declined from the peak of medium density(300-380 kg ha^-1),total biomass yield increased with density and then leveled off at 300,380 and 460.Our results showed that RFM system was significantly higher reproduction allocation and efficiency of conversion of vegetation into reproduction compared to conventional flat planting pattern?CK?.4.Effects of ridge-furrow ratio on wheat productivity,soil water and temperature under ridge-furrow with mulching plastic.The field experiment was composed of seven different levels of ridge-furrow ratios under ridge-furrow with mulching plastic?RFM?and flat plating with no mulching?CK?.The ridge-furrow ratios as follows:1)40:20,?R₄F₂?;2)30:20,?R₃F₂?;3)20:20,?R₂F₂?;4)30:40,?R₃F₄?;5)20:40,?R₂F₄?;6)30:60,?R₃F₆?and 7)20:60?R₂F₆?.The results showed that soil moisture and temperature decreased with the increases of ridge-furrow ratio.Compared with CK,the soil moisture storage under R₄F₂,R₃F₂,R₂F₂,R₃F₄ and R₂F₄ significantly increased,and soil temperature under R₄F₂,R₃F₂ and R₂F₂ were significantly higher than that under CK.RFM significantly increased wheat yield and water use efficiency,the increases under R₂F₂ was highest.Wheat yield under R₂F₂ increased by83.8%-90.3%compared to CK,and water use efficiency increased by103.7%-115.6%.Through nonlinear fitting,the maximum values of wheat yield,water use efficiency and harvest index appeared in the ridge-furrow ratio of 1.3-1.38,1.37-1.45 and 1.45-1.56,respectively.Wheat yield and water use efficiency decreased with the increase of ridge-furrow width by linear fitting.In summary,R₃F₂and R₂F₂ significantly improved the soil water and temperature conditions,and was the optimum ridge-furrow ratio for improving wheat productivity.5.Effects of ridge height on wheat productivity,soil water and temperature under ridge-furrow with mulching plastic.The field experiment was composed of three different levels of ridge heights?i.e.high ridge?HR?,medium ridge?MR?and low ridge?LR??under ridge-furrow with mulching plastic?RFM?and flat plating with no mulching?CK?.Soil moisture and temperature under the three ridge height treatments were significantly higher than those under CK.With the increase of ridge height,soil moisture increased,but the soil temperature decreased.Compared with CK,wheat yield and water use efficiency were significantly increased in all ridge height treatments.Wheat yield and water use efficiency were the greatest,and increased by82.8%-90.3%and 103.7-115.6%,respectively.The medium ridge significantly improved the soil water and temperature conditions,which could increase wheat productivity.6.Effects of nitrogen and phosphorus addition on wheat productivity under ridge-furrow with mulching system.This study was designed to explore the effects of farming system and nutrient addition.The farming system included ridge-furrow with mulching plastic?RFM?and flat plating?FP?.The nutrient addition was used four treatments as follows:control treatment without fertilizer addition?CK?,nitrogen addition?N?,phosphorus addition?P?,and nitrogen and phosphorus addition?NP?.We found that farming system,nutrient addition and their interactions had significant effects on wheat yield,biomass and water use efficiency.N,P and NP addition significantly increased wheat yield,biomass and water use efficiency both in RFM and FP farming system.For wheat yield,N,P and NP under RFM treatment increased by 75.5-80.4%,69.3-90.6%and 116.4-129.6%compared with CK,and N,P and NP addition under FP treatment increased by 76.5-135.3%,100-126.3%and119.3-169.5%,respectively.For water use efficiency,compared with CK,N,P and NP increased by 97.8-101.4%,94.1-114.5%and 155.5-181.3%in RFM system,and increased by 108.1-187%,137.5-179.2%and 208.6-261.3%in FP treatment,respectively.Among all nutrient addition treatments,RFM significantly increased wheat yield,biomass,and water use efficiency compared to CK.7.The effect of nitrogen and phosphorus addition on soil organic carbon soil quality under ridge-furrow with mulching system.N addition significantly decreased while P addition increased CO₂ emission,and N and P addition did not affect CO₂emission.N addition generally increased DOC and mineralized nitrogen content,led to soil acidification,decreased soil microbial biomass and enzyme activity,which suppressed SOC decomposition.P addition increased the content of DOC and AP,promoted the enzyme to decomposing soil cellulose,glucosamine,polyamine and lignin,decreased the APA,and finally enhanced SOC decomposition.Compared with FP,RFM significantly increased CO₂ emission,which was due to the increases in DOC,microbial biomass and enzyme activity.Compared with FP,RFM significantly increased soil soluble carbon,microbial biomass and enzyme activity,thus accelerated soil CO₂ emission.In sum,RFM combined mulching wheat straw improved soil hydrothermal conditions,increased the soil water and nutrient use efficiency,so that the better yield effect could be achieved.Meanwhile,it could increase the content of soil organic carbon and slow down the mineralization process of mulching plastic on organic matter,it is an innovative farming practice to improve field sustainable development.Tanken together,dual plastic and straw mulching system,planting density of 220 kg ha^-1,ridge-furrow ratio of 1-1.5,ridge-furrow unit size of 40 cm,ridge height of 15cm and rational nitrogen and phosphrous fertilization were the optimum RFM system in semi-arid regions of EAP.It is important in promoting farmland productivity and soil quality,and provides theoretical basis and scientific support for addressing climate change and food security in semiarid EAP.