| Water scarcity is one of abiotic factors that limits agricultural crop production in China. In China, Water-saving irrigation system can improve mechanization, automation, and pressure of water transportation. In Water-saving irrigation system, water seepage devices are put underground, facilitates water movement into soil profiles with negative pressure. Irrigation systems that use high filler material could save water and reduce energy consumption. However, the studies on negative pressure irrigation technology are limited in China. This study focused on soil water movement and water use of pakchoi and milk Chinese cabbage. To achieve this objective the negative pressure irrigation system(NPIS) developed by institute of Agricultural Resources and Agricultural Regionalization in Chinese Academy of Agricultural Sciences was used. The main conclusions of this study were as follows:(1)The research clarified the characteristics of water supply and mechanism of water active supply. NPIS uses soil water potential as power of water infiltration and it can supply water stably. During the growing period of crop, soil water potential was decreased by root water up take, so that the NPIS can supply water continuously and automatically.(2)Soil water content under negative pressure was less than that under conventional irrigation. NPIS supplied water smoothly and automatically during the growing period of crop. Furthermore, under negative pressure, soil moisture reduces with the increase of distance to water seepage device. Average soil moisture at 0-24 cm depth ranged from 15.7%~16.0%, the fluctuation is small.(3)Under negative pressure irrigation, pressure ranged from 20 to-5 k Pa, and soil moisture increased wilth pressure increase in the range of 3.6%~29.5%. Furthermore, soil moisture under same pressure was similar, and pressure can be controlled during crop growing period, therefore negative pressure can provide good soil environment for crop growth.(4)Soil moisture was constant under the same pressure, but significantly different among treatments. Water supply under-5k Pa and-10 k Pa was enough for crop growth, but-15 k Pa had negative effect. When the pressure set at-20~-5 k Pa, soil moisture can be control at 3.6%~29.5%. The NPIS can automatically control soil moisture in appropriate range, create good water and soil environment for crop growth in different growth stage.(5)The relationship between water supply and water consumption was y = 0.9849 x + 0.3865(R2 = 0.9987**), water consumption increased with soil moisture, and the relationship between soil moisture and water consumption was y = 1.2512x- 3.1677(R2 = 0.9669**), therefore water consumption increased with soil moisture. As the Increases of pressure crop water consumption increasing, water consumption of crop is the initiative of water supply.(6)NPIS can promote root growth, and leaf transpiration and photosynthetic rate. Water supply under pressure of-5 k Pa and-10 k Pa was enough for crop development ant its roots. However, under-15 k Pa, soil moisture was low, and then crop was under water stress. Furthermore, leaf net photosynthetic rate and transpiration rate were higher under-5 k Pa、-10 k Pa than other treatments. Correlations among factors were also analyzed. The results showed that net photosynthetic rate under-5 k Pa was mainly correlated with intercellular CO2 concentration, but net photosynthetic rate under-15 k Pa was related mainly to stomatal conductance and transpiration rate. Soil moisture under-15 k Pa was lower for stomatal conductance and transpiration rate so that the net photosynthetic rate declined.(7)Negative pressure irrigation can improve yield and vegetables quality. Average weight under-5 k Pa and- 10 k Pa was 40.2g, 62.4g for pakchoi and 110.9g, 139.5g for milk Chinese cabbage, respectively. Those weight were higher than weight recorded under other treatments. Compared with the traditional irrigation, weight of pakchoi was increased by 30%、108%, water use efficiency was improved by 35.3%、55.5%,vitamin C content was increased by 4.63%,61.3%, and nitrate content was decreased by 17.9%、21.4%, respectively. The change of soluble sugar contents was not regular.In view of yield, quality, water use efficiency, net photosynthetic rates, greenhouse irrigation under negative pressure for pakchoi and milk Chinese cabbage, optimal irrigation level-5~-10 k Pa could be promoted... |
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