| As a widely cultivated summer fruit,melons are very popular with consumers.However,the problem of applying excessive water and fertilizer in the blind pursuit of high yield still exists in production,resulting in large amounts of nutrient residues,seriously damaging the soil’s own structure,causing problems such as soil caking and salinization,and causing a decline in crop yield and quality while over-consuming water and fertilizer resources.Therefore,it is of great scientific and practical significance to investigate the coupling scheme of water and fertilizer application during the whole fertility period of melons in facilities,in order to achieve an environmentally friendly and resource efficient modern agriculture.In this study,‘Qianyu No.6’melon was used as the test material,and three irrigation levels were set according to the evapotranspiration(ETc)and the target yield method:(W1:low water,75%ETc;W2:medium water,100%ETc;W3:high water,125%ETc)and three fertilization levels(F1:low fertilizer,fertilization rate 758.44 kg/hm~2;F2:medium fertilizer,fertilization rate 948.05 kg/hm~2;F3:high fertilizer,fertilization rate1137.66 kg/hm~2),a total of 9 treatments.Field trials were carried out for two consecutive years(April-July 2020;April-July 2021)to determine the growth,yield,quality,water and fertilizer use efficiency and soil residues,to analyze the regulatory effects of water-fertilizer coupling,to establish a comprehensive evaluation system incorporating multiple types of characteristics based on correlation analysis,and to introduce the TOPSIS-GRA coupling model to evaluate the water-fertilizer application based on the multiple indicator system.The coupled water and fertilizer control model was established to obtain the optimal water and fertilizer treatment plan for melon cultivation,providing theoretical basis and production guidance for scientific irrigation of melon.The main research results are as follows:(1)The regulatory effects of water-fertilizer coupling on different indicators of melon.Fertilizer application had a significant effect on the net photosynthetic rate at flowering and fruiting,while irrigation,fertilizer application and their interaction all had a highly significant effect on the net photosynthetic rate at maturity;chlorophyll content was maximized under W1(low water)and F1(low fertilizer)conditions throughout the reproductive period;plant height and stem thickness showed an increasing trend with increasing water and fertilizer application,followed by a decreasing trend;T5(W2F2)treatment contributed most to the total dry mass at vine extension and maturity,while T8(W2F3)treatment performed best at flowering and fruiting.The T5(W2F2)treatment contributed most to the total dry mass at vine extension and maturity,while the T8(W2F3)treatment performed best at flowering and fruiting.Irrigation and fertilizer application and their interaction had a highly significant effect on fruit quality and yield per hectare(P≤0.01).Total soluble sugars and vitamin C content increased and then decreased with increasing irrigation and fertilizer application,soluble protein and soluble solids content decreased with increasing water,and free amino acid content reached a maximum in the T8(W3F2)treatment;tissue nitrate nitrogen content increased with increasing fertilizer application.Water use efficiency was significantly influenced by the amount of irrigation,with the lower the irrigation the higher the use efficiency;fertilizer bias productivity decreased with increasing fertilizer application.Soil nitrate-nitrogen and quick-acting phosphorus contents showed an increasing and then decreasing trend with increasing irrigation at the same fertilizer level,while quick-acting potassium contents showed an increasing trend with increasing irrigation at all three fertility stages.(2)Construction of a comprehensive growth evaluation system and weighting of indicators for melon.Based on correlation analysis,a comprehensive evaluation system integrating 17 sub-factors in five categories,namely growth,yield,quality,water and fertilizer efficiency and soil residue,was established.The subjective weights were assigned using hierarchical analysis,and the subjective weights at the criterion level were as follows:yield index(0.351)>growth index(0.240)>quality index(0.167)>efficiency index(0.146)>soil residue index(0.096);among the sub-factors,the subjective weight of yield per hectare was the largest(0.234),and the subjective weights of stem thickness at vine extension and tissue nitrate were the smallest(0.023).The objective weight of each indicator was determined based on the entropy weighting method,with the largest objective weight of ha yield for two consecutive years,the smallest weight of soluble protein in 2020,and the smallest weight of stem thickness at vine extension and chlorophyll at vine extension in2021.Based on the game-theoretic combination weighting method,the maximum weights were obtained for the two consecutive years,0.232 and 0.206,respectively,and the minimum weights were 0.007 for total dry mass at maturity in 2020 and 0.010 for stem thickness at vine extension in 2021.(3)Based on the coupled TOPSIS-GRA model,the overall evaluation of water and fertilizer treatments was based on the TOPSIS-GRA model,with T5(W2F2)being the maximum in both years and T6(W3F2)and T8(W2F3)ranking second in both years.Based on the TOPSIS-GRA coupled model,T5(W2F2)was the best treatment,with the other treatments ranked differently in the two years.The maximum difference in ranking between the three evaluation methods in the two years was 2 and 4 respectively,with a significant bivariate Spearman correlation.(4)Construction of water and fertilizer regulation model and analysis of the optimum application rate.Based on TOPSIS-GRA evaluation results,a water and fertilizer control model was established for melon with a parabola with a downward opening depending on the amount of irrigation and fertilizer application.The optimum water and fertilizer application interval was determined at 90%of the maximum value of the composite score for the whole fertility period of melon.In 2020,the fertilizer application rates were(221.50-270.72 m~3/hm~2,265.70-325.40 kg/hm~2)at vine extension,(354.42-433.18 m~3/hm~2,265.70-325.40kg/hm~2)at flowering and fruiting and(252.71-308.86 m~3/hm~2,354.26-432.40kg/hm~2)at maturity.In 2021,water and fertilizer for the three fertility stages are(195.62-239.10 m~3/hm~2,220.35-280.51 kg/hm~2),(270.57-330.69 m~3/hm~2,35.65-295.36kg/hm~2),(240.45-293.89 m~3/hm~2,309.33-397.84 kg/hm~2),when melon growth,yield,quality,water and fertilizer use efficiency and soil residue indicators are integrated and optimal. |
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