Regulation Effect Of Ridge-furrow Planting And Population Density On Soil Water,Heat And Nitrogen And Its Utilization Efficiency In Spring Maize Field In Semi-arid Region

Dryland agriculture is crucial for ensuring global food security,but low efficiency in water and heat resource utilization,low and unstable crop yields,and other issues remain the main challenges faced by dryland food production.Ridge-furrow mulching system significantly increases crop yield by improving soil water and heat conditions,and is widely used in spring maize production in arid areas of northwest China.Under this system,crop productivity is directly affected by the ratio of ridge-furrow ratios.Does the optimum population density of sirping maize change after using different ridge-furrow ratio?How do different ridge-furrow ratio and plant density regulate crop productivity and recourse use efficiency?These scientific questions need to be addressed.This study conducted field experiments in the mountainous areas of southern Ningxia from 2020 to 2021,setting up three ridge-furrow planting modes R6F6,R8F4,and R5F1（representing ridge-furrow ratios of 60:60 cm,80:40 cm,and 50:10 cm,respectively）and bare land flat planting without film covering（CK,control）and three population densities(L:low density 67500 plants ha^-1;M:medium density 82500 plants ha^-1;H:high density 97500 plants ha^-1)in a two factor completely randomized block experiment.Analyzed indicators such as soil water and heat conditions,root growth and respiration characteristics of spring maize,plant nitrogen uptake,productivity,resource utilization efficiency,and economic benefits,aiming to provide reference for improving resource utilization efficiency in semi-arid areas and achieving sustainable agricultural production.The main results and conclusions are as follows:（1）The higher the ridge-ridge ratio,the higher the soil water content during the spring maize growth period,especially the soil water content before silking stage was significantly increased.R6F6,R8F4 and R5F1 were 2.7%,3.3%and 5.7%more than CK in 0-200 cm soil layer,respectively.With the increase of population density,soil water content decreased gradually,and the water storage under M and H density was 4.0%and 8.2%lower than that under L,respectively.The soil evapotranspiration（ET）of R6F6,R8F4 and R5F1 was 13.9,21.5 and 30.3 mm higher than that of CK,respectively.ET at M density is the largest,45.8mm and 53.1 mm more than L and H,respectively.In terms of soil moisture balance,only R5F1 played an effective role in soil moisture conservation in two years of average ridge-furrow planting.Ridge-furrow planting also increased the surface soil temperature（0-20cm）,and the higher the ridge-furrow ratio,the higher the soil temperature.The average daily temperature of R6F6,R8F4 and R5F1 during the growing season was 0.8,2.1 and 3.7℃higher than that of CK,respectively.The rdige-furrow planting mainly increased the soil temperature from 31 to 90 days after maize sowing,and the effective soil accumulated temperature of R5F1 was 1.4 times that of CK at this stage.（2）The higher-furrow ratio,the greater the increase of root length density（RLD）,root surface area density（RSD）and root dry weight density（RDD）,and the greatest effect was found on 0-20 cm root system.Increasing ridge-furrow ratio also promoted root respiration and CO₂ emission（TCO₂）increase.The respiration rate of R6F6,R8F4 and R5F1 was 1.3,1.5 and 1.6 times that of CK,and the respiration rate of TCO₂ was increased by 62.7%,53.1%and 56.0%,respectively.With the increase of population density,the respiration rate and TCO₂ both increased first and then decreased,and the effect of changing population density on the respiration rate of ridge-furrow planting was the highest,and the effect of changing population density on the respiration rate was less than that of CK,and the TCO₂ of R5F1-M was the highest in two years.The carbon emission efficiency（CEE）of ridge planting in2020 is lower than that of CK,and the CEE of CK in 2021 is lower than that of ridge-furrow planting because the grain yield in CK is almost extinct.The CEE in ridge-furrow planting was lower with higher population density,and CEE in L was 3.0%and 8.0%higher than that in M and H,respectively.The correlation analysis showed that the root morphological characteristics were the most correlated with root respiration,and RLD explained 94-99%of respiration.Ridge-furrow planting reduced the sensitivity coefficient Q₁₀ of respiratory temperature,and the higher the ridge-furrow ratio,the lower the Q₁₀,and the correlation between soil moisture and respiration was the weakest.（3）Ridge-furrow planting significantly increased the leaf area index（LAI）,dry matter biomass per plant and dry matter accumulation at harvest stage of spring maize,which drove the effective transformation proess of resources.The ratio of grain to dry matter yield of R6F6,R8F4 and R5F1 were 15.5%,15.7%and 10.4%higher than CK,respectively.The grain yield was mainly dependent on the accumulation and transport of above-ground dry matter after spinning.At L and M densities,the transport rates of R8F4 and R5F1 were both higher than those of CK,and the transport rates of R8F4 were 7.7 and 2.5 times of CK,and8.9 and 2.8 times of R5F1,respectively.The increase of population density increased the proportion of leaf in dry matter accumulation,and the increase of leaf proportion in M and H density was 1.2-27.1%and 2.8-28.5%higher than that in L,respectively.The change of density had no significant effect on the accumulation and transport of dry matter,and the input of dry matter accumulation into grain after spinning was the highest in M density in two years,which was 13.2%and 21.4%higher than that in L and H.The number of grains per ear,100-grain weight and grain yield of spring maize were significantly increased by ridge-furrow planting,and the grain yield was affected mainly by changing the number of grains per ear.The grains per ear of R6F6,R8F4 and R5F1 were43.8%,50.6%and 48.4%more than CK,respectively.With the increase of population density,the number of grains per ear and the 100-grain weight decreased.The grain yield of R5F1 was significantly higher than that of R6F6,and the grain yield of R8F4 and R5F1 was93.2%and 111.8%higher than that of CK,respectively.After increasing population density,grain yield first increased and then decreased.The effect of population density on grain yield of CK was greater than that of ridge-furrow planting,and the highest grain yield of 12026kg ha^-1 could be reached under R5F1-M.The coefficient of variation（CV）of biological yield,number of grains per ear,100-grain weight and grain yield of spring maize was decreased by ridge-furrow planting,and the sustainability index（SYI）was increased,indicating that the higher ridge furrow ratio was,the better yield stability and sustainability was.CV is the smallest and SYI is the largest in M density,and the stability and persistence are the best.（4）The increase of ridge-furrow ratio increased the total nitrogen uptake of spring maize.The nitrogen uptake of R6F6,R8F4 and R5F1 was significantly increased by 75.1%,92.6%and 101.6%compared with CK.The total nitrogen uptake of each ridge-furrow planting mode was the highest under M density.The total nitrogen uptake of R5F1-M reached the maximum in both years.Increasing ridge-furrow ratio and population density both reduced soil nitrate nitrogen content at harvest stage.The nitrate nitrogen content in 0-200 cm soil layer in R6F6,R5F1 and R8F4 treatments was 19.7,12.2 and 8.8 kg ha^-1 less than that in CK,respectively,which reduced soil nitrate leaching loss.The increase of population density reduced the difference of nitrate nitrogen amount between ridge-furrow planting and the increase of population density had less effect on nitrate nitrogen than CK.Ridge-furrow planting also reduced the total nitrogen content in 0-60 cm soil layer during the harvest period.The difference of total nitrogen accumulation in ridge-furrow planting under M density was the largest compared with CK.Among the three population densities,the total nitrogen accumulation was the least under M density,the CK accumulation under L and H density was 52.2%and 2.6%lower than that under M,and the CK accumulation in ridge-furrow planting was 54.1-59.3%and 3.3-8.2%lower,respectively.The effect of population density change on the total nitrogen accumulation in ridge-furrow planting soil was higher than that of CK.（5）Ridge-furrow planting increased water use efficiency（WUE）,precipitation use efficiency（PUE）,grain level heat use efficiency(TUE_GY),biomass level heat use efficiency(TUE_DM),nitrogen fertilizer partial productivity（NPFP）,absorption efficiency（NUPE）,and nitrogen use efficiency（NUE）of spring maize.Compared with CK,WUE and PUE increased by 169.5%and 191.8%,TUE_GY and TUE_DM by 89.9%and 43.6%,and NPFP,NUPE and NUE increased by 56.5%,55.1%and 57.2%,respectively.WUE,PUE and NUPE of R5F1 are significantly higher than those of R6F6 at the three densities.The increase of ridge-furrow ratio and population density increased the production input,but the increase of total output was much larger than the increase of production input.The higher the ridge-furrow ratio is,the higher the net income increases.The net income of R6F6,R8F4 and R5F1 is 4570,5429 and 6655 yuan ha^-1 more than that of CK,respectively,and the yield to investment ratio is 1.5,1.6 and 1.7 times that of CK.After increasing the population density,the net income firstly increased and then decreased.The net income under M density was the highest,which was 587 and 1552 yuan ha^-1 more than L and H density,respectively.Based on the research results of soil hydrothermal environment,root and root respiration,crop production and resource utilization by different ridge-furrow ratio,it was found that increasing ridge-furrow ratio improved soil hydrothermal environment,increased land carrying capacity,stimulated underground root growth and respiration,promoted the absorption of soil moisture and nutrients,and increased maize yield and resource utilization efficiency.In addition,optimizing population density in suitable ridge-furrow ratio can make full use of limited water,heat and nutrient resources,maximize crop yield and resource utilization efficiency,and realize the goal of high yield and sustainable production.Overall consideration,the ridged-furrow ratio was 50:10 cm,and the population density of 82500ha^-1 plants was the most efficient use of soil water,heat and nitrogen resources,and the yield sustainability,resource use efficiency and economic benefit of spring maize were the best.Especially,the increase effect of spring maize yield and resource use efficiency was better in the years with less precipitation in the early growth period of spring maize,which could be used as a cultivation management measure for spring maize in the Loess Plateau.