| As the largest rain-fed agricultural area in China,the Loess Plateau has a special regional climate that severely limits the improvement of crop productivity.As an efficient micro-catchment planting strategy,ridge-furrow plastic-film mulching planting（RFPM）has high applicability in rainfed agricultural production on the Loess Plateau,and has achieved good expected results.The ridge-furrow unit is the core configuration of this planting pattern,and determining a reasonable ridge-furrow ratio is essential to further improve this planting pattern and increase crop productivity.We adopt the research idea of combining meta-analysis and field experiment.First,the meta-analysis was used to quantify the average effects of different ridge-furrow ratios（ridge-furrow ratio>1,<1,and=1）on soil water and heat,crop yield and water use efficiency and identify the key driving factors affecting its effect,and further guide the field experiment based on the results.In addition,nitrogen application rate was identified as the key factor affecting the effect of ridge-furrow ratio（based on meta-analysis）,and different ridge-furrow ratios will create different hydrothermal environments,and whether this can produce a positive synergistic effect of"determining fertilizer with water and promoting water with fertilizer"with nitrogen application rate,thereby improving crop productivity,there is no clear conclusion.Two planting patterns and three N application rates were tested in the field experiment.The two planting patterns were flat planting（FP）and RFPM with three different ridge-furrow ratios（40:70?cm（RF40-70）,55:55?cm（RF55-55）,and 70:40?cm（RF70-40））.The three N application rates were 180?kg?ha-1（N1）,240?kg?ha-1（N2）,and 300?kg?ha-1（N3）.By clarifying the comprehensive effects of two factors on field soil environment,the phenology,canopy establishment,root growth and development,root-shoot relationship,root activity and water use pattern,water and nitrogen absorption and utilization,yield and economic benefits of spring maize,and then determine ridge-furrow ratio and nitrogen application rate combination suitable for rain-fed spring maize production on the Loess Plateau.The main conclusions of this study are as follows:（1）Through Meta analysis,it was concluded that compared with FP,ridge-furrow ratio>1 had the best effect on soil water storage and warming.Compared with FP,ridge-furrow ratios>1,=1 and<1 significantly increased crop grain yield by 37.65%,27.12%and 31.70%,and significantly increased WUE by 47.70%,30.00%and 17.80%,respectively.Based on crop grain yield and WUE,the effect of each ridge-furrow ratio was influenced by a combination of climatic factors,soil properties and field management.When the mean annual precipitation is greater than 600 mm and the mean annual temperature is greater than 12℃,the ridge-furrow ratio<1 has a better effect,and conversely,the ridge-furrow ratio>1 has a better effect.Soil bulk density,organic matter and total nitrogen content were the key factors affecting the effects of the three ridge-furrow ratios,but soil available nutrients had no significant effect.The positive effects of the three ridge-furrow ratios were greatest at moderate nitrogen application rates and increased with increasing phosphorus application rates,but were not affected by potassium application rates.The results also showed that ridges coverage could be used as the coverage pattern for the three ridge-furrow ratios.The above results have important reference value and reference significance for the optimization of ridge-furrow configuration and the development of field experiments.（2）In this study,soil temperature showed obvious spatial and temporal heterogeneity,and was only affected by the ridge-furrow ratio but not by nitrogen application rate.The warming effect of the three ridge-furrow ratios was not continuous,and generally decreased with the advancement of the growth process.In the early stage,compared with FP,RF40-70,RF55-55 and RF70-40 increased the temperature of the 5 cm soil layer by1.02°C,1.95°C and 2.25°C,and the 15 cm soil layer temperature by 1.21°C,1.90°C and2.48°C,respectively.In general,the larger the ridge-furrow ratio,the greater the improvement of soil water content,especially in the 0-100 cm soil layer,the average increase of RF40-70,RF55-55 and RF70-40 was 4.70%,9.15%and 11.67%,respectively.Increased nitrogen fertilization reduces soil water content,which risks exacerbating drought stress.The increase of nitrogen application rate increased the content and accumulation of NO3--N and total nitrogen in each soil layer,but the increase of ridge-furrow ratio had a tendency to decrease both.In addition,the increase of ridge-furrow ratio and nitrogen application rate both increased the organic matter content of the topsoil,which may be caused by the increase of root biomass.The above results show that optimizing the ridge-furrow ratio and nitrogen application rate can improve the soil hydrothermal environment,reduce the risk of nitrogen loss,and provide a more efficient and comfortable resource acquisition environment for spring maize growth.（3）The results showed that the ridge-furrow ratio and nitrogen application rate had obvious effects on the phenological period of spring maize.Under the N1 application rate,the three ridge-furrow ratios advanced the emergence time of spring maize by 4-6 days compared with FP;the increase of nitrogen application rate prolonged the reproductive growth stage of next spring maize in the three ridge-furrow ratios,which resulted in 1-4days longer the growth days of spring maize in the three furrow ratios under N2 and N3application rates.The increase of ridge-furrow ratio and nitrogen application rate was beneficial to expand the establishment of aboveground canopy of spring maize,including plant height,leaf area and dry matter accumulation.Under the three nitrogen application rates,compared with FP,RF40-70,RF55-55 and RF70-40 increased the net photosynthetic rate by 9.52%,15.72%and 21.88%,respectively.The increase of nitrogen application rate also increased the photosynthetic rate,however,there was no significant difference between N2 and N3 nitrogen application rates.Under the same nitrogen application rate,compared with FP,the three ridge-furrow ratios all increased the final grain weight by prolonging the active filling period,but the increase of nitrogen application rate was not conducive to grain filling.The above results indicated that optimizing the ridge-furrow ratio and nitrogen application rate could improve the growth process,canopy establishment and assimilate accumulation in the shoots of spring maize,laying a physiological basis for the improvement of productivity.（4）In this study,the increase of ridge-furrow ratio and nitrogen application rate significantly promoted root growth in the 0-40 cm soil layer.For root length density,surface area density and dry weight density,under three nitrogen application rates;compared with FP,RF40-70 increased by 21.48%,34.37%and 24.21%,respectively;RF55-55 increased by 35.18%,55.53%and 33.91%,respectively;RF70-40 increased by47.50%,74.82%and 42.40%,respectively.Compared with FP,the increase of ridge-furrow ratio increased the distribution proportion of spring maize roots in shallow soil layer（0-20cm）,but the increase of nitrogen application promoted the distribution ratio of roots in deep soil layer（60-100 cm）.The increase of ridge-furrow ratio and nitrogen application rate both increased root activity,and correlation analysis showed that this was related to the improvement of root characteristic parameters.In this study,the root-shoot ratio was only affected by the planting pattern,and showed different trends in different growth periods.In the early stage of growth（V6）,the three ridge-furrow ratios significantly increased the root-shoot ratio compared to FP,which was beneficial for the root system to absorb more nutrients for the rapid establishment of the canopy;however,in the middle and late stages of growth（VT,R3 and R6）,the three ridge-furrow ratios reduced the root-shoot ratio and distributed more assimilates to the shoots,which was beneficial to the formation of yield.The above results indicated that optimizing the ridge-furrow ratio and nitrogen application rate could promote root growth,and optimizing the root-shoot relationship could promote the distribution of shoot assimilates.（5）In this study,the water isotope(δD andδ18O)tracer technology was used to analyze the root water use patterns and related root characteristic parameters of spring maize under different planting patterns.Compared with FP,the two furrow-furrow ratios（RF40-70 and RF70-40）did not change the main water-absorbing soil layers of spring maize roots in each period.From the perspective of the whole growth process of spring maize,the main water-absorbing soil layer of the root system presents a trend of"shallow layer-middle layer-shallow layer",which is related to the growth and development of spring maize root system,its own water demand and the availability of soil water.Based on the"Mix SIAR"model,the water absorption of spring maize in each soil layer was quantitatively analyzed.Compared with FP,RF40-70 and RF70-40 increased the water absorption proportion of spring maize roots in shallow soil,but decreased the water absorption proportion in deep soil.This phenomenon is related to the change of water and heat environment in shallow soil and the distribution proportion of root parameters.In addition,we also found that the root water uptake pattern was mainly related to root length density and surface area density,but not root weight density.（6）Spring maize productivity had a strong response to planting pattern and nitrogen application rate.Under the three nitrogen application rates,compared with FP,RF40-70,RF55-55 and RF70-40 significantly increased grain yield by 11.91%-13.95%,20.00%-20.48%and 27.47%-30.03%,respectively.An increase in nitrogen application rate was beneficial to an increase in grain yield,but RF70-40 showed no significant difference between N2 and N3.The response of nitrogen accumulation to two factors showed the same trend as grain yield,but the increase of nitrogen application rate decreased the allocation proportion of grain nitrogen,and under N3,the allocation proportion of grain nitrogen decreased with the increase of ridge-furrow ratio.Under the three nitrogen application rates,compared with FP,the three furrow-furrow ratios significantly improved nitrogen fertilizer partial productivity（Nf P）and nitrogen uptake efficiency（Nup E）,which increased with the increase of furrow-furrow ratio.However,Nf P and Nup E followed the law of diminishing returns and decreased with the increase of nitrogen application rate.The increase of ridge-furrow ratio and nitrogen application rate both led to an increase in the production cost,but since the total output showed an opposite trend and was much larger than the input of the production cost,which led to the highest net benefit under the combination of RF70-40 and N2 or N3.Based on grain yield and WUE,compared to other planting patterns,RF70-40 had a lower nitrogen input threshold,that is 268.56 kg ha-1-274.14 kg ha-1.This study clarified the response of spring maize productivity to the combined effect of ridge-furrow ratio and nitrogen application rate,and revealed the potential ecological and physiological mechanism of productivity change from the perspectives of soil environment,growth and development of spring maize,root growth and activity,root-shoot relationship and water absorption pattern.In general,RF70-40 combined with nitrogen application rate of 268.56 kg ha-1-274.14 kg ha-1 showed high productivity,and could be recommended as a field management strategy for rain-fed spring maize production in the Loess Plateau. |
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