| The gully land construction project on the Loess Plateau has effectively alleviated the shortage of cultivated land area in the Loess Plateau watershed.In recent years,the cultivated land area has been increased by 7848.72hm2,and 28233.29hm2 of high-standard farmland has been built.However,due to the interweaving influence of perennial rainfall,slope runoff and adverse drainage facilities,the water level in the ditch treatment project area rises year by year,coupled with high regional evaporation,the risk of soil secondary saline-alkali increases,and part of newly created farmland has been affected by soil secondary saline-alkali.Therefore,how to effectively improve soil secondary saline-alkali and ensure high yield and harvest of typical crops is of great significance to regional agricultural production and ecological environment construction.In this paper,the newly created cultivated land in Gutun watershed of Baota District,Yan ’an City,Shaanxi Province was selected by the method of soil column experiment and field experiment,and four different amendments including he kang(HK),humic acid(HA),yan ke(YK)and biochar(NB)were selected.Based on the multi-process water-fertilizing-salt migration process simulation and mechanism analysis,such as infiltration,evaporation,water and salt migration,etc.It is intended to analyze the improvement efficiency and mechanism of various improvers through the dual dimensions of physical structure optimization and chemical performance improvement;The effects of modifiers on the soil environment and yield of maize fields were analyzed by combining the characteristics of water,fertilizer and salt changes,crop growth characteristics and nutrient accumulation and transport characteristics of crop organs,and the mechanism of the type and amount of amendments on the improvement of maize farmland environment was explored;Finally,based on the game theory,AHP(subjective)and entropy weight method(objective)were used to achieve the combination of subjective and objective weights.Weighted TOPSIS method and fuzzy comprehensive evaluation method were used to conduct comprehensive evaluation of soil environment improvement of typical crops in the saline-alkali soil area of gully treatment land on the Loess Plateau.In order to provide a theoretical basis for soil improvement in saline-alkali soil and the mechanism of promoting energy efficiency of typical crops.The main research contents are as follows:(1)The effect mechanism of four kinds of amendments and their dosages on water and salt transport characteristics was revealed.The cumulative infiltration and wetting front migration distance per unit time decreased significantly compared with the control under the four amendments and different application amounts,and the same amendments showed a decreasing trend with the increase of application amounts.The residual water content(θr),saturated water content(θs)and suction related parameters of soil increased in different degrees compared with the control,and the residual water content(θr)increased by 2.93%—31.67%,indicating that the four modifiers retained more water under very low water potential.The soil shape coefficient n showed a decreasing trend compared with the control.Compared with the control,the saturated water content of soil increased by 0.68%to 6.48%,indicating that the application of four amendments could increase the water holding capacity of soil.In the evaporation test,the evaporation rate of the four amendments and the application amount decreased significantly compared with the control(P<0.05),and in the same duration,the evaporation rate decreased with the increase of the application amount,and the soil salt content decreased significantly by 0.78%—13.75%.(2)The dynamic transport law of soil water and salt distribution in root zone of maize,a typical crop in Loess Plateau,was investigated.The volume water content of 0-30cm soil profile under the four amendments and different application amounts increased significantly compared with the control,and increased by 1.35%—16.95%(2019)and 1.91%—14.84%(2020)at maturity stage,respectively,and reached the maximum value when the amount of modifiers was the maximum.Compared with the control,the salt content in 0-30cm soil profile decreased to different degrees.In the maturity stage,the salt content decreased by 3.20%—30.76%(2019)and 4.14%—24.82%(2020),respectively,and it first increased and then decreased with the advance of growth period.The soil desalting rate increased to different degrees compared with the control,and the average desalting rate was 13.76%(2019)and 29.23%(2020),respectively.The variation of soil volume water content in 0-30cm soil profile at different growth stages under the effect of different modifiers conforms to the quadratic regression equation of one variable,which decreases first and then increases.(3)The regulation effects of four modifiers on the growth indexes,abovemorded and underground biomass,dry matter accumulation and root distribution of maize were expounded.The indexes of plant height,stem diameter and leaf area index of maize under 4 kinds of modifiers and different application amounts were significantly increased compared with the control group,and the index values reached the maximum when the amount of modifiers was the maximum.The dry matter quality of above-ground and underground parts of corn also increased in different degrees compared with the control.The treatment of HK,YK and NB increased first and then decreased with the increase of application amount.Root length was the most sensitive to soil amendments,followed by root mass and root volume.The growth and development of maize plant height,stem diameter and leaf area index under the treatment of different modifiers were consistent with the curve model,that is,the growth of maize plant height,stem diameter and leaf area index showed a significant "S" shaped curve with the growth period.Principal component analysis was used to analyze the effect of the type and dosage of amendments on maize growth promotion.It was found that the promoting effect of modifiers in descending order was HK>NB>YK>HA>CK.(4)The response mechanism of four amendments to the accumulation and distribution of soil nutrients and plant salinity in the root zone of maize,a typical crop in the Loess Plateau,was systematically analyzed.The nutrient concentrations(available nitrogen,available phosphorus and available potassium)in 0-25cm soil profile increased significantly under different application amounts of the 4 modifiers,and showed an increasing trend with the increase of the application amount of the 4 modifiers.The available nitrogen concentrations increased by 23.40%(2019)and 19.79%(2020)from jointing to filling stage in maize season.The concentration of available phosphorus increased by 21.56%(2019)and 18.20%(2020);The concentration of available potassium increased by 19.11%(2019)and 18.22%(2020).The rule of different nutrient utilization efficiency of maize plants from large to small showed phosphorus>potassium>nitrogen,and the rule of nutrient absorption efficiency from large to small showed potassium>nitrogen>phosphorus.The analysis of the effect of 4 modifiers on nutrient absorption and utilization showed that,The maximum utilization rate of nitrogen,phosphorus and potassium increased by 20.86%(NB),32.81%(HA)and 19.04%(HA),and the maximum absorption rate of nitrogen,phosphorus and potassium increased by 32.86%(HK),27.13%(NB)and 26.21%(HK),respectively.(5)Based on principal component analysis,the regulatory effects of 4 modifiers on yield,aboveground biomass,harvest index,water use efficiency and partial fertilizer productivity were clarified.The yield,aboveground biomass,harvest index,water use efficiency and partial fertilizer productivity of the four amendments and different application amounts increased in different degrees compared with the control,and the application of HK,YK and NB showed a trend of increasing first and then decreasing.The net income also increased in different degrees compared with the control,among which the average net income of HK treatment was the highest,with an increase of 3027 yuan(2019)and 3649 yuan(2020)per hm2,respectively.The net income in 2019 and 2020 also showed the same rule,namely HK>YK>HA>NB>CK.Based on the comprehensive analysis results of the type and dosage of modifiers by principal component analysis,the average scores were as follows:HK(0.928)>NB(0.160)>YK(0.059)>HA(-0.305),and the highest dosage of the same type of improvers were 140kg/hm2(HK),125kg/hm2(HA),140kg/hm2(YK)and 200kg/hm2(NB),respectively.(6)Based on game theory,AHP(subjective)and entropy weight method(objective)were used to assign weights,and weighted TOPSIS method and fuzzy comprehensive evaluation method were used to carry out comprehensive evaluation of the type and amount of soil modifiers on the improvement of maize farmland soil environment.The results showed that TOPSIS method and fuzzy comprehensive evaluation method had the same comprehensive evaluation index ranking.He kang ranked first,the recommended best dosage is 140kg/hm2.The second is yan ke,the best recommended dosage is 140kg/hm2.The third is biochar,the best recommended dosage is 200kg/hm2.From the comprehensive perspective of saline-alkali land control,soil environment improvement and farmers’ income improvement,He kang soil modifier can be used in the secondary saline-alkali area of ditch land treatment on the Loess Plateau,and the best dosage is recommended to be 140kg/hm2. |
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