| The Loess plateau is a typical semi-arid region,and an important grain producing area in China.Limited and erratic precipitation has long threatened the productivity and sustainability of crops,often resulting in reduced or even failed production.Meanwhile,the low temperature in spring and autumn and unscientific nutrient management in this region often restrict the growth and development of crops,which further aggravates the stress on farmland production.Population pressure,social development and environmental security are increasingly urgent for efficient and sustainable food production in China.Hence,how to promote the coordinated and efficient utilization of water,heat,radiation and nutrient resources and realize the sustainable production of farmland is an important research problem faced by dryland agriculture in the semi-arid Loess plateau.Aiming at the common constraints of available water,heat and nutrients on agricultural production in the Loess Plateau and the uncertainty of maize productivity driven by them,this study carried out field experiments for four consecutive years in the southern mountainous region of ningxia hui autonomous region from 2014 to 2017.By setting two field experiments:1)three different plastic film mulch planting patterns?ridge-furrow construction with full plastic film mulching,RFF;ridge-furrow construction with half plastic film mulching,RFH;flat planting with half plastic film mulching,FH?,and flat planting with no mulching,FN,as the control,and 2)five fertilization levels(N0+P2O5 0 kg ha-1,CK;N 117+P2O5 59 kg ha-1,L;N 173+P2O5 87 kg ha-1,M;N 229+P2O5115 kg ha-1,H;N 285+P2O5 143 kg ha-1,SH)under the RFF and RFH mulch planting patterns,to study the effects of different mulch planting patterns and fertilizer application on soil temperature and water,maize growth and development,photosynthetic characteristics,nutrients absorption,grain yield,water and nutrients use efficiency,and economic benefits,investigate the soil hydrothermal driving mechanism of mulch planting to improve the cooperative utilization of water,heat,radiation and nutrient resources,explore the influence mechanism of fertilizer application on sustainable resources utilization and maize productivity under mulch planting.The study can provide scientific basis for understanding the crop physiological response to water and heat,crop modeling,perfecting the technology of mulching planting,agricultural regionalization,and water and fertilizer matching management.The main results and conclusions are as follows:?1?Response characteristics of soil thermal to mulch planting,and the growth and development of maizeMulch planting increased the soil temperature at 10 cm depth,and the average daily soil temperatures under RFF,RFH and FH during maize growth period were increased by2.9?,1.9?and 1.5?,respectively,compared with the control FN.As maize grew,the soil temperature increase under mulch planting showed a decreasing trend,which was 2.42.3 and 1.8 in the vegetative growth stage and reproductive growth stage,respectively.In addition,the thermal insulation effect at night?20:00-08:00?was stronger than that increase effect at day?08:00-20:00?,caused the diurnal temperature variation to decrease by 0.7-1.3oC,which thus alleviated the sudden change of soil temperature,with the strongest capacity under RFF followed by FH,and RFH was the weakest.By statistical analysis of soil temperature and air temperature,it was found that mulch planting showed the strongest warming capacity in the low temperature range of 5-10 oC,with a warming effect of 2.5 oC.Meanwhile,mulch planting increased the distribution frequency of soil temperature in20-25 oC range,and that 5-20 oC was decreased,which significantly improved the soil thermal environment of maize growing.Mulch planting obviously accelerated the growth and development of maize,shorten the growth period by 2-17 days,and meanwhile advance emergence?VE?by 2.5-6 days,,jointing?V6?by 4-10 days,and silking?R1?by 4-13 days,and with the shorten and advance abilities ranking:RFF>FH>RFH.Although shortening the vegetative growth period by 8-13 days,mulch planting still maintaining an equivalent duration in reproductive growth,with RFF and RFH shortened by 3.5 and 2 days,respectively,RFH extended by 2 days.?2?Spatio and temporal dynamic change strategy of soil water to drive efficient photosynthesis by mulch plantingMulch planting significantly improved soil water conditions and drove soil spatio-temporal wet-dry alternations that an efficient water use strategy.At temporal perspective,the soil under mulch planting showed an alternating trend of relatively wet,dry and wet during 0-50 days,50-130 days and 130-160 days after sowing?DAS?,respectively,compared with that under no mulch control;whereas at spatio perspective an alternating trend of relatively wet,dry and wet in the soil layers of 0-20 cm,20-120 cm and 120-200cm,respectively,compared with that under no mulch control,during the 50-130 DAS.Compared with RFH and FH,RFF driving a trend of strong wet?SWC increased by0-2.0%?,moderate dry?SWC decreased by 0.4-1.5%?and thus moderate dry?SWC increased by 0-0.9%?,showing a stronger water balance ability.Although mulch planting decreased soil moisture in the water-sensitive stage,it still significantly improved the net photosynthetic rate by 12.4-52.9%,transpiration rate by12.6-59.2%and stomatal conductance by 17.9-120.5%of maize in the stage,and leaf area index and dry matter accumulation increase as well.?3?Effects of mulch planting on co-utilization mechanism of water,heat,radiation and nutrient resources,and maize productivity.Mulch planting significantly improved the maize resource capture during the growth period,increased the interception of photosynthetic effective radiation?PAR?by 6.3-11.8%,the effective soil temperature?TTsoil?by 129-389 oC d,and the nitrogen uptake by8.8-21.7%,and the evapotranspiration?ET?did not increase significantly,with the greaest capacity in RFF followed by RFH and FH,.By driving positive soil thermal response,mulch planting created an excellent thermal environment for maize growing,and further drove efficient water utilization strategies on the basis of improving water availability,which improves the matching degree of soil water and crop water requirements.At the same time,mulch planting was affected by positive thermal effect to shorten the vegetative growth duration but maintain?even extend?equivalent reproductive growth duration,improved the phenology of maize,promoted the enrichment of water,thermal,radiation and nutrient production resources to the reproductive growth of maize,which drive the acquisition and optimal allocation of resources in semi-arid study areas,as well as the transformation of resources into biological materials?especially grains?.Compared with RFH,FH and FN control,RFF increased grain yield by 24.6%,20.4%and 42.7%,respectively;water use efficiency?WUEGY?by 24.0%,21.7%and 42.5%,respectively;thermal utilization efficiency by 15.0%,12.0 and 20.2%,respectively;radiation use efficiency by 19.7%,15.6%and 34.8%,respectively;and nutrient use efficiency?NUE?by17.4%,12.7%and 26.5%,respectively.?4?Effects of fertilizer application under RFF and RFH on growth and development,and water and nutrients uptake of maizeCompared with RFH,RFF obviously accelerated the growth of maize,with the growth duration shortened by 17 days.Under the two mulch planting patterns,fertilization extended maize growth period,with the reproductive growth duration extended by 9 days,11 days,14 days and 15 days respectively under L,M,H and SH,compared with CK.With the increase of fertilizer application,the SPAD value,photosynthetic rate,plant height,leaf area index,and dry matter accumulation of maize increased,but no significant improvement was found after exceeding H level.In addition,Fertilization dominated the difference in photosynthetic characteristics between the years,which might cause the factors that restricted photosynthesis of maize gradually shift from stomatal conductance to stomatal density and quality over time.Four years on average,the evapotranspiration?ET?of RFF during maize growth period was 8 mm higher than that of RFH and 15.7 mm,which was lower than the soil water increase during the leisure period,indicating a higher water balance capacity.Fertilization significantly increased the water uptake by maize,and ET increased from433.3 mm at CK level to 479.0 mm at H level higher than SH level.However,the average precipitation during the growth period was only 404.8mm,a decrease of 28.5-74.2 mm compared with ET;if so the soil water increase of 32.9-51.2mm during the leisure period could not balance the difference between ET and precipitation,which led to the water imbalance and soil water content gradually decreased,and intensified with the increase of fertilizer application.Compared with RFH,the total N and P uptake in RFF increased significantly,while the nutrient content decreased,with an average decrease of 9.8%in N and 6.9%in P,but the precentages decreased with the increase of fertilizer application.Fertilization significantly improved the content of N and P nutrients in plants under RFF and RFH,and increased the total N uptake by 1.0-2.4 times and the P uptake by 0.6-1.3times,achieveing the highest level in SH fertilization level that no significant difference with H level.The nitrogen and phosphorus harvest index was decreased by increasing fertilizer application.?5?Maize yield,water and fertilizer utilization efficiency,water and fertilization matching,and water availability deficit warning under RFF and RFHCompared with RFH,RFF significantly increased maize grain yield by 21.8-43.9%and WUEGY by 21.6-42.4%,which increased first and then decreased with the increase of fertilization level.With the increase of fertilization level,maize grain yield showed an increase trend,reaching the highest yield of 8741.3 kg ha-1 in the RFF at N 226.8+P2O5113.4 kg ha-1,and that of 6931.9 kg ha-1 in the RFH model at N 295.7+P2O5 147.9 kg ha-1.Thus,compared with RFH,RFH showed obvious effect of fertilizer decreased(amount:N68.9+P2O5 34.5 kg ha-1;percentage:23.3%)but yield increased”(amount:1782.4 kg ha-1;percentage:25.7),indicating the superiority of RFF planting methods.Also,WUEGY showed a similar trend to yield,and an effect of fertilizer decreased but efficiency increased as well.Compared with RFH,RFF significantly increased N use efficiency?NUE?by24.8%,uptake efficiency by 13.4%,productive efficiency?NUPE?by 33.4%?fertilizer use rate by 8.0%,while those under P were increased by 5.2%,27.8%,33.7%and 32.2%,respectively.With the increase of fertilization level,the nutrient utilization efficiency of RFF and RFH showed a decreasing trend,and the H and SH levels dropped significantly to the low level.Fertilizer use rate and fertilizer yield contribution rate increased at first and then decreased,reaching the highest at M and H levels,indicating the recommendability of nutrient strategy at M to H fertilization level.ET was significantly positively correlated with fertilizer application,grain yield,WUEGY and soil moisture?SWSS?before sowing,but significantly negatively correlated with SWSS,indicating that coordinating fertilizer application and SWSS to obtain reasonable ET was beneficial to sustainable water use and sustainable crop productivity.Although the highest yield and water and fertilizer utilization can be achieved at a higher level of fertilization?H or SH?,the soil water balance capacity determined by regional precipitation requires fertilization to match it.With the increase of fertilizer application,the annual soil water balance gradually changed from surplus to deficit,and RFF and RFH reached the critical point of water balance at N 180.9+P2O5 90.5 kg ha-1 and N 121.0+P2O560.5 kg ha-1,respectively,achieving 97.7%and 78.3%of their respective yield potential,respectively.Moreover,to ensure the sustainable water use and crop in maize production,in addition to controlling the amount of fertilizer applied,it is also necessary to guarantee the water availability?SWSS+precipitation 0-X DAS?in critical period.Under RFF,the water availability deficit warning threshold of SWSS,SWSS+precipitation 0-30 DAS,SWSS+precipitation 0-60 DAS and SWSS+precipitation 0-90 DAS were 441.1 mm,488.3 mm,558.8.3 mm and 624.3 mm,respectively,while those under RFH were 367.3mm,426.1 mm,505.3 mm and 564.1 mm respectively.If the water availability is lower than the warning threshold,supplementary irrigation measures should carried out to avoid growth restriction or even production failure.Although RFF?compared to RFH?and fertilization?compared to non-fertilization?increased production inputs,they resulted in a larger increase in output value and thus higher net income.However,under current mulch planting,the supply of water and fertilizer in farmland should be carefully managed,because the mismatch of water and fertilizer will reduce economic benefits and even lead to serious economic losses.Under RFF planting,the balanced fertilizer application of N 180.9+P2O5 90.5kg ha-1 matched with regional precipitation was relatively close to the fertilizer application of N 206.3+P2O5103.2 kg ha-1 at which the highest economic benefits was obtained,which proves the considerable economic benefit characteristics of balanced fertilization from the perspective of economic benefits,so it can be considered as the recommended fertilizer application.In a comprehensive consideration,compared with RFH,RFF can maintain soil water balance based on local rainfall at a higher fertilizer application rate,and show a sustainable water-fertilizer coupling effect for increasing yield,efficiency and income.Therefore,RFF+N 180.9+P2O5 90.5 kg ha-1 is recommended as an efficient planting management scheme in the semi-arid areas of the Loess Plateau,and attention should also be paid to the water availability within 0-90 DAS.Longer term?>4 years?efficient management programmes or water,heat and nutrient management in combination with mulching and other agronomic measures should be based on evidence from soil quality studies and improvements in farmland production facilities. |
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