Water Requirement And Optimal Irrigation Index For Effective Water Use And High-quality Of Tomato In Greenhouse

Greenhouse technology can contribute to utilize the resources such as light, heat, water and soil in various ways and provide with an optimum environmental medium for crop growth. With the rapid economic development and the improvement of people's living conditions, people pay more attention to the vegetables quality and non-polluted production. With increasing shortage of water resources, water-saving irrigation technologies mainly in drip irrigation were used in greenhouse vegetable production more and more, and showed an importance and superiority. Base on the current economic situation, water requirement and optimal irrigation index for effective water use and high-quality of tomato in Greenhouse were studied in this paper, which can improve the development of water-saving irrigation and water use efficiency on vegetables in greenhouse and achieve the vegetable products with high-yield and high-quality by water. At the same time, these studies will play an important role in improving high efficient utilization of water and fertilizer and production profit.Tomato, as a vegetable crop, being cultivated in a wide range of region and greater acreage, was regarded as the main research object in this study. The experiment was carried out in a greenhouse in 2008 and 2009 at the water requirement experimental station of Farmland Irrigation Research Institute. Tomatoes were transplanted in wide-narrow row plantation method. According to the growth characteristics of tomato, it was divided into three growing stages, such as vegetative growth stage, flowering and fruit development stage and fruit maturation stage. On the same basis of irrigation endpoint of 90% (taking up percentage of field water capacity), there were three different irrigation water levels (irrigation start point was 50%, 60% and 70%, respectively) at the vegetative growth stage, and four different irrigation water levels (irrigation start point was 50%, 60%, 70% and 80%, respectively) at the flowering and fruit development stage and the fruit maturation stage, respectively. In additiona, an adequate water treatment (irrigation start point was 80% for the whole growing season) was designed as a control. The experiment was laid out in a randomize block design consisting of ten treatments and three replications.Plant growth situation, physioecological characteristics, soil evaporation, plant transpiration, final yield, fruit quality and water use efficiency were investigated with field laboratory experimental data got in two years. The main results were as following:(1) Water deficit at any growth stage decreased photosynthetic rate and stomatal aperture of tomato leaves, furthermore, affected the accumulation and transportation of dry matters, but influencing pattern and degree of water stress were not same at the different growth stages. Water stress inhibited tomato growth and development at the vegetative growth stage, but too enough water led to plant spindling and over growth and affected photosynthate transportation to the fruit. Water stress at the flowering and fruit development stage not only inhibited tomato growth, but also reduced dry matter accumulation, and affected the yield formation. Water deficit at the fruit maturation stage accelerated tomato plants aging, decreased the ultimate amount of dry matters, and affeted yield formation obviously. Therefore, moderate soil moisture can not influence tomato normal growth and physiological water requirement, can inhibit plant excessive growth of tomato and has an advantage of transporting photosynthate to fruit and providing a good base for yield formation.(2) Water deficit (50%～55% of field capacity) occurred at the vegetative growing stage increased fruit numbers and decreased the percentage of malformed fruit, but reduced fruit size generally. Fruit maturation also were delayed and concentrated mainly in the later picking period. During flowering and fruit development stage, severe water deficit (less than 65% of field capacity) promoted tomato fruit maturation, but reduced fruit numbers and increased the risk of forming small fruit and malformed fruit. At the fruit maturation stage, too high (more than 80% of field capacity) or too low (less than 65% of filed capacity) soil moisture both reduced tomato yield, but had few effects on fruit maturation. Too low soil moisture also decreased fruit numbers and increased the percentage of malformed fruit.(3) There was a close relationship between tomato water consumption and soil moisture (water treatment) in greenhouse under drip irrigation. Water consumption was decreased with soil moisture whether in the whole growth season or at any stage. A quadratic function relation with correlation coefficient above 0.90 was showed between tomato yield and water consumption or amount of irrigation in the whole growth season. Economic water consumption ranged from 311.83mm to 348.18mm for the greenhouse grown tomato.(4) There was a difference of fruit quality among the different picking time for the same water treatment in the whole picking process. Quality traits in the whole picking stage would be not represented by one fruit quality value that existing in each treatment. Therefore, takeing the average value of the fruit quality measurement in several times can eliminate differences in the different picking time to a certain extent.The effects of soil moisture at different growth stages on fruit storage-transportation quality (firmness) and nutrition quality (such as sugar-acid ratio, vitamin C content, soluble protein content, nitrate content, etc.) varied, which was little at the vegetative growing stage and large both at the flowering and fruit development stage and fruit maturation stage. Overall, fruit firmness and VC content increased with the degree of water deficit imposed, and a negative linear relationship was observed between these two indexes and water consumption. There was a lower convex second-degree parabola relation between nitrate content and water consumption, but a upper convex second-degree parabola relation between sugar-acid ratio and water consumption. However, the effect of soil moisture on soluble protein content was little in this study. Therefore, water regulation can improve some fruit quality in a certain extent.(5) Soil evaporation and plant transpiration were affected by meteorological condition, soil water moisture and tomato growth status. It was showed that a positive exponential correlation existed between soil evaporation and meteorological factors such as solar radiation, air temperature and vapor pressure difference. Daily sap flow rate had a positive linear correlation with daily solar radiation, and a logarithm relationship with vapor pressure difference. Soil evaporation was negatively exponential correlated with leaf area index, sap flow rate was positive linear correlated with leaf area index, and the obvious interweave changes was showed between soil evaporation and plant transpiration. The study also showed standardized sap flow rate can express the plant transpiration of tomato well.Based on Penman-Monteith equation and the existing research results, the parameters such as canopy stomatal resistance of tomato and aerodynamic resistance were modified in connection with a microclimate environment in greenhouse, and the estimation model of transpiration for greenhouse grown tomato was established by considering the meteorological data, leaf area index and canopy height as main parameters. The model was verified by measurement values of sap flow rate from May 2 to 13 in 2009 (at the flowering and fruit development stage) and from June 9 to 20 in 2009 (at the fruit maturation stage), respectively. The result showed that average relative error for the model simulation was 8.48% and 9.20% at two stages, respectively. Therefore, plant transpiration can be estimated using the model.With the analysis of water requirement and its influence factors for greenhouse grown tomato, the estimation model for water requirement was established for the first time based on the meteorological data. The model was verified by measurement values of transpiration and soil evaporation from May 2 to 13 in 2009 (at the flowering and fruit development stage) and from June 9 to 20 in 2009 (at the fruit maturation stage), respectively. The result showed that average relative error of the model was less than 10%. Based on the model for estimating water requirement, the evapotranspiration model was established by introducing soil moisture correction coefficient K(θ) when water deficit occurred.(6) Taking yield, water use efficiency, single fruit weight, fruit firmness, sugar-acid ratio, VC content as the main evaluation indicator and using the principal component analysis method, the lower limit index of soil water was determined with achieving high yield, high fruit quality and efficiency for greenhouse grown tomato. The lower limit index value of soil moisture was 60%-65%, 70%-75% and 70%-75% of field capacity at the three growth stages of tomato, respectively.