| Considering the status quo of low water and fertilizer use efficiency by greenhouse vegetables, as well as the needs of developing a high-efficiency agriculture with low irrigation and fertilizer, this study aims to explore the optimal irrigation and fertilization system with high yield, quality and efficiency synchronously. Through plot test and theoretical analysis, the water and fertilizer use by greenhouse tomato was studied. There were two fertilization types(drip fertigation and conventional fertilization), with three drip irrigation levels(high irrigation, W1, 100% ET0; medium irrigation, W2, 75% ET0; low irrigation, W3, 50% ET0) and three fertilizer levels(high fertilizer, F1, N240-P2O5120-K2O150 kg/hm2, medium fertilizer, F2, N180-P2O590-K2O112.5 kg/hm2, low fertilizer, F3, N120-P2O560-K2O75 kg/hm2). The influencing mechanism and coupling effects of different supply modes of irrigation and fertilization on water and nutrient migration in the root zone, nutrient effectiveness, dry matter accumulation, nutrient uptake, yield and quality of tomato were explored. Based on that, the principal component analysis, grey correlation analysis and multiple regression analysis were used to comprehensively evaluate the indexes high- yield, high-quality and high-efficiency, and to explore the optimal irrigation and fertilizer amount and the appropriate supply mode of water and fertilizer. The main results were as follows:(1) Tomato growth indicators had interactio n effects. There were highly significant positive correlations between plant height and aboveground dry matter, plant height and total chlorophyll, aboveground dry matter and total chlorophyll, stem diameter and the root parameters, but they exhibited different trends during the growth. The plant height and stem diameter increased simultaneously; the leaf extension rate reached the maximum 40 days after transplanting; dry matter in different organs increased constantly; the root weight density, total root volume and the average diameter exhibited increasing trend; the total root length and total root surface area reduced 60 days after transplanting and began to increase 70 days after transplanting; the chlorophyll a, chlorophyll b and total chlorophyll significantly increased 49 days after transplanting, but reduced 67 days after transplanting; the carotenoid reached the minimum 67 days after transplanting. Therefore, the tomato plants should be promptly irrigated and fertilized 40 to 67 days after transplanting to ensure plant growth and yield increase.(2) The influence of irrigation and fertilization on tomato growth was revealed. The growth of plant height and stem diameter was significantly inhibited by low fertilizer. The F2 treatment significantly increased the leaf growth rate, dry matter and root-shoot ratio during the second and the third fruit enlargement period. The W2 treatment showed the largest leaf number. As irrigation water increased, the F2 treatment significantly increased the root parameters, with the largest values during late growth period. The C hlorophyll a, chlorophyll b, carotenoid and total chlorophyll were positively related to the fertilizer rate. The differences among the fertilizer treatments increased constantly as plants grew up. The peak value in the W1 and W3 treatments occurred earlier, whilst the W2 treatment reached the peak late in full bearing period. Low irrigation and fertilization significantly reduced aboveground growth indicators. Compared to conventional fertilizatio n, drip fertigation increased dry matter in middle and late growth period by 13.2%~20.1%.(3) The maximum tomato yield was 97.15 t/hm2. The yield and fruit weight per plant markedly increased with the increase of irrigation and fertilizer amount. The corre lation of yield and fruit number per plant was significantly greater than that of yield and fruit weight per plant. The fruit weight per plant significantly increased with the increase of fertilizer and irrigation amount at the high irrigation and fertilizer levels. Compared to conventional fertilization, drip fertigation increased fruit weight per plant, fruit number(by 1.16 per plant) and tomato yield(by 8.2~18.5 t/hm2). Except the sugar acid ratio, the indexes of tomato quality decreased with the increase of irrigation amount. The Vitamin C, lycopene, soluble sugar and sugar acid ratio under drip fertigation first increased and then reduced as the fertilizer rate increased, with the maximum in the W3F2 treatment. The indexes of tomato quality in other treatments were positively related to the fertilizer rate, with the maximum in the W3F1 treatment. The organic acid and nitrate content under conventional fertilization was greater than under drip fertigation. During tomato production, the measures that increased the fruit number were beneficial to tomato yield. High fertilizer and appropriately reduced irrigation water could give consideration to both yield and quality. Drip fertigation can effectively achieve the goal of high yield and good quality.(4) Water consumption was significantly influenced by irrigation rather than fertilization. The water consumption differences among different fertilizer rates were less than 5.4 mm, with the maximum of 292.89 mm. The maximum water use efficiency(WUE) and partia l factor productivity of fertilizer(PFP) were 47.66 kg/m3 and 311.04 kg/kg, respectively. Irrigation had greater effect on WUE than fertilization, but fertilization had greater effect on PFP than irrigation. Reducing irrigation amount and increasing fertilizer amount would improve WUE and reduce PFP. WUE and PFP significantly reduced when irrigation water was higher than the W3 treatment(0.5ET0) and fertilizer rate was greater than the F3 treatment(N120-P2O560-K2O75 kg/hm2). Compared to conventional fertilization, drip fertigation reduced water consumption by 9.25 mm, and increased WUE by 2.9~10.9 kg/m3 and PFP by 19.38~44.16 kg/kg. Appropriate increase of irrigation water and fertilizer rate would improve the WUE and PFP to a large extent.(5) The nitrogen and phosphorus accumulation in different organs were as follows: root>leaf>stem>fruit. The potassium accumulation in the stems was greater than in the leaves. Increasing irrigation water and fertilizer rate would increase nutrient accumulation. The potassium accumulation in the W1F1 treatment was significantly greater than that in other treatments. The F3 treatment significantly reduced the nitrogen and phosphorus accumulation. The F2 treatment had the largest phosphorus and potassium accumulation in the second fruit enlargement period. Compared to drip fertigation, conventional fertilization promoted the nutrient accumulation in the flowering and fruit bearing, the first and second fruit enlargement periods, but reduced the nutrient accumulation in the harvesting period. Increasing irrigation water and reducing fertilizer rate could improve the nutrient uptake efficiency, but decreasing irrigation and fertilizer amount could increase nutrient use efficiency. The results indicate that drip fertigation can significantly improve the nutrient uptake in late growth stage, but the irrigation water and fertilizer rate should be controlled reasonably.(6) Increasing irrigation water and reducing fertilizer rate could reduce the soil nitrate nitrogen, available phosphorus and available potassium content. Irrigation and fertilization significantly affected the soil nutrient content 0~59 days after transplanting under conventional fertilization. The N itrate nitrogen accumulated at the lateral boundary of the wetted volume, which was larger in the upper soils under conventional fertilization. The F2 treatment exhibited the minimum nitrate nitrogen content. The available phosphorus content was smallest in the soil and was rarely identified below 40 cm depth. The available phosphorus and available potassium content were the biggest all the time under dripper, and quickly reduced along horizontal and vertical direction. There was little difference between the F2 and F3 treatments. The available potassium content in the soil under conventional fertilization was smaller than under drip fertigation 59 days after transplanting. The soil nutrient content under conventional fertilization was higher than under drip fertigation at the beginning of growth stages, but lower in the har vesting period. The differences among soil layers reduced as plants grew up, and the difference between two fertilization types decreased continuously. Reasonable control of irrigation and fertilization to a large extent could improve plant nutrient uptake and reduce the soil nutrient residues under drip fertigation, which could maintain the sustainable development of soil environment in greenhouse.(7) The principal component analysis and grey correlation analysis showed the consistent results in terms of comprehensively evaluating tomato growth, yield, quality, water and fertilizer use efficiency. The W1F1 treatment with irrigation 270.8 mm and fertilizer rate N240-P2O5120-K2O150 kg/hm2 was the best combination for drip fertigation, and the W2F1 treatment with irrigation 213.1 mm and fertilizer rate N240-P2O5120-K2O150 kg/hm2 was the best combination for conventional fertilization. The low fertilizer treatment F3 with N120-P2O560-K2O75 kg/hm2 should be eliminated for both fertilization types. The multiple regression analysis showed that the optimum tomato indicators were obtained with irrigation 212.6 mm and fertilizer rate 461.1(N217.0-P2O5108.5-K2O135.6) kg/hm2 for drip fertigation, and irrigation 246.96 mm and fertilizer rate 463.9(N218.3-P2O5109.2-K2O136.4) kg/hm2 for conventional fertilization. |
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