| Under global climate change,significant inadequacy in food production ability and on-field rainwater collection in semiarid east African Plateau?EAP?has aroused widespread concerns.In semiarid area of west China,especially in the Loess Plateau?LP?,an advanced farming management system,i.e.ridge-furrow?RF?mulching system has demonstrated a substantial potential to boost local maize production over last decade,owing to its high-efficient rainwater harvesting and utilization,low-cost input and high economical profitability.However,whether this system is effective and feasible in semiarid EAP remains an unanswered fundamental question.On the other hand,the impacts of balanced fertilization and cultivar maturity group on crop yield and water use efficiency under RF system are still unclear.The clarification on those questions aforementioned is not only the kernel of dryland agriculture theory research,but also the strategic demands of the B&R project.Therefore,based on typical RF mulching practices including RF with transparent film mulching?RFT?,RF with black film mulching?RFT?,RF with straw mulching?RFT?and RF with no mulching as CK,a series of field experiments and technical validation were conducted in EAP and LP during 2012-2014 growing seasons.We first introduced Chinese RF system to EAP through incorporating two key issues of local dryland maize production,i.e.cultivar selection and fertilization management.Two seemingly independent but tightly linked field factorial experiments were established in a semiarid farm of Kenya in 2012 and 2013 growing seasons.In first trial,three maize cultivars with different maturity group?early-,mid-and late-maturing cultivars?were planted under four alternative ridge-furrow mulching patterns?RFT,RFB,RFS and CK?.For the second one,according to local fertilization practice,three different rates of compound fertilizer application(high level: F2,375 kg ha-1;tranditional level: F1,225 kg ha-1;no fertilization as F0)were imposed to the three RF practices as RFT,RFB and CK.In order to explore the mechanisms of improved crop productivity in EAP due to introduced RF system with balanced fertilization and cultivar selection,a series of critical agronomic and ecological parameters were measured as following: soil water storage,soil thermal balance,crop water consumption and utilization,soil carbon pool,soil enzyme activity,crop phenology pattern,growth indicators,biomass accumulation and distribution,yield and components,reproduction efficiency,grain nutrition absorption,water/fertilization use efficiency and economic benefits and so on.In addition,based on the mechanism study above,a few of optimal season-specific technique combinations of RF system with cultivar selection and fertilization level were identified and recommended in dryland maize production in EAP.Finally,to conduct an accurate risk evaluation in course of RF introduction from LP to EAP,a contrastive analysis was performed through repeating a paralleled cultivar × RF system factorial experiment at Shitougou station in LP in 2014 growing season.The capacities of soil water storage/utilization,soil organic carbon balance,phenology modification,reproductive success and economic benefit output were compared between EAP and LP.The findings presented could be expected to set up a theoretical basis for promoting effective innovation and improvement on introduced RF system in EAP in recent future.For one thing,the potential mechanism contributed to improved dryland maize productivity due to RF system can be summarized as following:1.RF film mulching not only extended duration of soil water availability,but also established a dynamic model of evapotranspiration suitable crop water consumption.Compared to CK,RFT and RFB increased topsoil water storage by 48.9% and 49.9%,along with a significant improvement in sub-and deep-soil moisture.Crop water consumption at late growth stages were also significantly enhanced in film-mulched plots.Importantly,both RFT and RFB reduced evaporation-based evapotranspiration of maize field in early growing season by 18.8,19.0 mm,but significantly increased evapotranspiration in late season by 21.2 mm and 19.1mm respectively,compared to CK.2.The season-specific selection on different plastic film improved soil thermal balance to facilitate crop growth and reproduction.Compared to CK,RFT in relatively cool 2012 growing season averagely increased soil temperature?10 cm depth?by 1.3? through warming effect of transparent film.Conversely,in 2013 with a relatively warm climate,RFB averagely reduced soil temperature by 0.5? due to cooling effect of black film mulching.More significant temperature reduction was recorded in heading stage of maize growth,which could provide an ability to heat resistance.3.The dynamic balance of soil organic carbon?SOC?was confirmed to be neutral and soil enzyme activity was consistently enhanced under RF system.Both RFT and RFB increased SOC consumption within growing season by 0.7,0.8 g kg-1,while tended to accelerate SOC recovery during fallow season in a greater magnitude in comparison with CK.The soil enzyme activities of catalase,polyphenol oxidase and urease were 6.6 mg g-1,47.0 mg kg-1 and 1.0 mg g-1 higher in RFT plots,7.8 mg g-1,51.4 mg kg-1 and 0.9 mg g-1 higher in RFT plots than those under controlled plots.4.RF with film mulching moulded an optimized maize phenology pattern through compacting crop vegetation duration but extending reproductive growth.Compared to un-mulched control,both RFT and RFB significantly improved maize emergence rate by 8.1% and 7.8%,shortened the duration from sowing to heading by 11.2 and 9.4 days respectively.While the reproductive duration in RFT and RFB was extended by 5.6 and 5.3 days compared to CK respectively.5.RF with film mulching signgificantly improved plant establishment and seedling vigour,as well as above-and under-ground biomass accumulation,eventually optimized reproduction allocation.Both RFT and RFB improved the ability on longitudinal growth and horizontal expansion of maize stem development,as well as increased leaf area index.As a result,above-and under-ground biomass under RFT and RFB were significantly increased by 56.6% and 6.36%,37.2% and 45.1% respectively,compared to CK,which may increase potential of grain yield and root-derived carbon input.RFT and RFB increased the allocation proportion of maize reproductive parts by 12.1% and 14.5% compared to CK respectively.6.RF with film mulching significantly improved ear formation and reproductive success,ultimately increased yield output and harvesting index.Both RFT and RFB clearly improved ear length,ear diameter,kernel number per ear,kernel weight per ear,grain nitrogen content and phosphorus contents by 16.1% and 19.6%?11.0% and 12.7%?13.9% and 16.8%?56.8% and 51.8%?34.3% and 31.8%?36.8% and 27.3% respectively compared to CK.Kernel abortion under RFT and RFB was also reduced by 6.4% and 6.4%.Thus,grain yield and harvesting index under RFT and RFB plots were 69.9% and 78.5%,0.095 and 0.067 higher than those in un-mulched plots.7.RF with film mulching supported high-level resource utilization and economic output,especially for use of water/fertilization use efficiency.Under RFT and RFB,water use efficiency,N and P fertilizer utilization efficiency and net incomes were increased on average by 98.4% and 99.7%,3.2% and 4.0%,1.2% and 1.2%,47.3% and 39.2% compared to CK respectively.8.Improved soil water availability due to RF system that enable late-maturing cultivar to increase uptake to sub-soil water in the middle of crop development,deep-soil water at late growth stages,leading to a significant higher in-season water consumption.Maturity group did not significantly affect the seasonal dynamics of SOC and soil enzyme activity.Late-maturing maize enlarged the advantage of extended reproductive duration and revealed the ability of significantly improved biomass accumulation.However,final grain yield exhibited apparent seasonality,mainly due to differential improvement magnitudes in yield components,reproductive input and efficiency.Specifically,in long rainy season with a relatively desirable environment,late-maturing maize achieved the greatest yield output,water use efficiency and economic benefit,through improving yield components,increasing reproduction output,lowing kernel abortion and delaying leaf senescence.Conversely,early-maturing maize showed best performances through advancing reproduction,declined kernel abortion and increased reproduction efficiency in environment-stressed short rainy season.9.Under RF with mulching system,increased fertilization promoted crop water uptake from sub-soil profile at reproduction stages.Higher fertilization level significantly reduced SOC loss within growing season but increased SOC recovery during fallow season.With the increase in fertilization,leaf senescence was alleviated and biomass allocation to ear was increased.While,moderate fertilization consistently kept greater N-and P-fertilizer use efficiency,indicating an obvious limitation of fertilizer utilization and absorption by crop in EAP.Higher fertilization level could lead to significantly improved grain yield,water use efficiency and economic benefit in long rainy season,while this advantage in short rainy season was insignificant in comparison with moderate level,the possible reason should be inadequate crop growth,advanced senescence and increased reproduction limitation under drought and heat stresses.10.Based on the agronomic and ecological mechanisms aforementioned and hydrothermal conditions in different seasons,we therefore proposed a few of season-specific technique combination in the perspective of optimal yield output and economic benefit as following: late-maturing maize cultivar grown under high fertilization application and transparent film mulching in long rainy season,but early-and mid-maturing cultivars combined with moderate fertilization level and black film mulching in short rainy season.Last but most important,the results from our comparative study further revealed the challenges in the process of technique introduction from China to EAP,mainly included: compared to LP,a)the capacities of soil water storage,crop water consumption and use efficiency were significantly lower by 24.6%,34.7% and 51.4%;b)SOC in EAP exhibited apparent decline within growing season and clear recovery tendency during fallow season,reducing stability of soil carbon balance;c)Maize growth in EAP subjected a more severe early corp senescence and lower reproductive allocation?4.1% lower than LP?,as well as greater magnitude in kernel abortion rate;d)any high-yield cultivar with longer growing cycle could not demonstrate their full yield potential in EAP;e)the increases in economic benefit and ratio of output to input in EAP were still at a low integrity owing to limited yield improvement.Therefore,to further improve the high efficiency and stability of introduced RF mulching system in EAP,it can not be overlooked that future work would be needed in order to address those related issues. |
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