| Tomato is one of the major economic vegetables in cultivation of solar greenhouse in Northwest China. It is important to use reasonable irrigation method and accurate water-nitrogen coupling to supply water and nitrogen punctually and properly according to the requirements in the process of tomato growth. This helps improve tomato yield and water and nitrogen use efficiency and will be of great importance in improving fruit quality and protecting ecological environment.We studied the effects of different irrigation methods and water-nitrogen couplings on the growth, yield, quality, root characteristics, accumulation of dry matter and nutrient uptake of tomato through experiment method and theoretic analysis. The main results are as follows:(1) Increasing water and nitrogen amounts was conductive to the growth of plant height, stem diameter and leaf area of tomato in alternate partial root-zone irrigation and conventional irrigation. Compared to conventional irrigation, the alternate partial root-zone irrigation optimazed plant morphology, improved stem diameter and the plant resistance to lodging and inhibit the redundancy vegetative growth. The accumulations of plant height, stem diameter and dry matter exhibited a Logistic curve over time. The duration of fast accumulation period for stem diameter in spring-summer season was shorter than that in autumn-winter season, therefore, it was better to have frequent, small amounts of water and nitrogen supplied in autumn-winter to avoid thin and high plant morphology, tomato in spring-summer was just the opposite. The alternate partial root-zone irrigation reduced growth rate and maximum accumulation rate, regulated the growth of plant height and stem diameter to be slow and order.(2) Under the two irrigation methods( alternate partial root-zone irrigation and conventional irrigation), the trends of root dry weight, stem dry weight, leaf dry weight and the total dry weight were similar with the increasing of water and nitrogen, they firstly increased and then decreased. Compared to conventional irrigation, the alternate partial root-zone irrigation improved tomato biomass and increased yield. The total dry matter of tomato and the amounts of water and nitrogen supply exihibited a binary quadratic regression relationship, the maximum of dry matter was found in W3N2 treatment.(3)The chlorophyll content firstly increased and then decreased over time, the maximum was found in fruit enlargement stage. Compared to conventional irrigation, the chlorophyll content was higher in alternate partial root-zone irrigation. With the increasing of water and nitrogen, chlorophyll content firstly increased and then decreased. Increasing irrigation water appropriately improved the tomato photosynthesis and more nitrogen relieved inhibition of drought to photosynthesis, excessive nitrogen strengthened the restrain from drought. Compared to conventional irrigation, the alternate partial root-zone irrigation improved Pn and Ci and reduced Gs and Tr which achieved high water ues efficiency and reasonable yield. The regulation of alternate partial root-zone irrigation to photosynthetic characteristics was significant under W1 condition and N3 condition.(4)Tomato yield per plant was higher in spring-summer and alternate partial root-zone irrigation. More water and nitrogen could relieve and remedy the decline of yield caused by drought and nitrogen deficiency, the tomato yield per plant and the water and nitrogen supply exihibited a binary quadratic regression relationship, this indicated that yield was not always increasing with the increase of water and nitrogen. The water and nitrogen amounts which achieved maximum yield were 82.9% and 89.4% of that achieved maximum dry matter. With the increasing of water and the decreasing of nitrogen, water use efficiency reduced while nitrogen production efficiency improved.(5)The alternate partial root-zone irrigation stimulated root compensation function and promoted root growth. The root length, root surface area and root volume of tomato could be presented by a Logistic curve over time. Root length, root surface area and root volume were not increasing all the time with the increase of water and nitrogen, their maximum was found in W2N2 treatment respectively. Tomato root can be classified by diameter as follows: D≤0.1 mm, 0.1~0.2 mm, 0.2~0.5 mm, 0.5~1 mm, 1~2 mm, 2~5 mm and D≥5 mm. With the increase of diameter class, the ratio of root length decreased, the ratio of root surface area firstly increased and then decreased, the maximum ratio of root volume was obtained with D≥5mm. Through regression analysis a significant positive correlation was obtained between yield and root characteristics, different degrees of correlations between yield and root characteristics in different diameter ranges was also obtained.The grey correlation analysis showed the order of correlation between root characteristics and yield was root length, root dry weight, root surface area and root volume.(6)Soluble solids decreased with the increasing of water while lycopene, nitrate and sugar-acid ratio firstly increased and then decreased. With the increasing of nitrogen, organic acid and nitrate increased and lycopene, nitrate, sugar-acid ratio firstly increased and then decreased. By using entropy weighting method, the objective weights of six single quality attributes were ranked based on their importance by lycopene>sugar-acid ratio>soluble sugar>organic acid>soluble solids>Vitamin C in autumn-winter. There existed a significant positive correlation between soluble solids and soluble sugar, Vitamin C and lycopene, Vitamin C and soluble sugar, lycopene and soluble sugar, organic acid and nitrate. The better quality was achieved with irrigation upper limit of 70%~80% of field capacity and nitrogen supply of 0.36 g N per kilogram dry soil.(7) The order of tomato nutrient uptake in the end of fruit picking stage was N、K、P. Increasing water and nitrogen amounts improved plant nutrient uptake. The nitrogen concentration in tomato aboveground biomass increased with the improving of applied N rates, and decreased in the growing process. The relationship between the aboveground biomass and N concentration can be described by the power exponent, appropriate irrigation could improve the capacity of plant for nitrogen. Based on the model of nitrogen nutrition(NNI) and the model of N uptake, we concluded that the W2N2 treatment was optimal. The order of distribution rate of N、K、P in various organs was leaf, stem and root. The stepwise analysis indicated that there was a positive correlation between phosphorus uptake amount and root dry weight, potassium uptake amount and stem dry weight, nitrogen uptake amount and leaf dry weight.(8) Leaf phosphorus content had a significant positive correlation with soluble solids, and a negative correlation with organic acid. There also existed a positive correlation between Leaf potassium and lycopene. The canonical correlation analysis showed that the increase of leaf nitrogen content might increase Vitamin C, organic acid and nitrate, the increase of leaf phosphorus content improved soluble solids, the increase of leaf potassium might cause increase of lycopene.(9) To achieve high yield and quality and saving water, the spatial analysis method was used, we came into a conclusion that it could obtain high yield and quality of tomato with the irrigation amount of 58.8~63.8L/plant(70%~80% θf)and nitrogen supply of 13.6~17.1g/plant(0.36 N g?kg-1)in spring-summer season. The average principal component analysis indicated that W2N2 treatment was optimal with the irrigation level of 60%~75% θf and nitrogen level of 0.30 N g?kg-1 in autumn-winter season, our research provided the optimal water-nitrogen coupling for tomato cultivation in different crop rotation in solar greenhouse of Northwest China. |
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