Suitable buried depth of drip irrigation improving yield and quality of tomato in greenhouse

Abstract: Studies of the impact of subsurface drip irrigation on tomato growth paid more attention to the effects of subsurface drip irrigation and integration of water and fertilizer on root growth, yield and water use efficiency, but the responses of yield and fruit quality to root growth, plant growth and photosynthate allocation were rare. To understand the interaction between “ground part - underground part - yield and quality” in the process of crop growth, explore the inner mechanism of the subsurface drip irrigation, reasonably allocate drip irrigation measures, and further refine water management measures, this paper performed field experiments to investigate tomato plant growth, root growth, photosynthate allocation, fruit yield and quality, and water use efficiency response to different buried pipe depth in subsurface drip irrigation with conventional ground drip irrigation as reference (CK), and analyzed the effects of plant growth, root growth, and photosynthate allocation on fruit yield and quality. The field experiment was conducted in the sunlight greenhouse of Dazhai Village, Dazhai Township, Yangling District, Shaanxi Province from October, 2014 to May, 2015. The greenhouse was 108 m in length (in the east-west direction) and 8 m in width (in the south-north direction). The soil compositions in experiment were as follows: 25.4% gravel (>0.02-2 mm), 44.1% silt (0.02-0.002 mm), and 30.5% clay (<0.002 mm). The physical properties of the soil were as follows: bulk density, 1.35 g/cm3; field moisture capacity, 28.17% (mass fraction of water in soil); and soil porosity, 49.38%. The test crop was tomato, and the cultivar was “Haiti”, which was cold resistant variety. Test plots were built from west to east in the greenhouse, 2 ridges per plot; and the ridge was 6.0 m in length, 0.6 m in width and 0.2 m in height, divided by a ditch with the width of 0.3 m. The area of each plot was 3.4 m2. Thirty-four plants were planted in 2 rows, with a plant-spacing of 0.35 m in each plot and protection rows at each end of the plot. The experiment had 4 treatments: 1) Surface drip irrigation with plastic film mulching (control, CK) - the drip irrigation pipe was installed in the middle of the tomato rows, with an irrigation lower limit of 70% of field capacity and an irrigation upper limit of 75% of field capacity; 2) and 3 subsurface drip irrigation treatments with plastic film mulching - the drip irrigation pipe was installed in the middle of the tomato rows at a depth of 10 cm (S10), 20 cm (S20) or 30 cm (S30); given that subsurface drip irrigation is more water-saving than surface drip irrigation, the irrigation lower limit was set at 60% of field capacity, and the irrigation upper limit was set at 65% of field capacity. Each treatment had 3 replicates, with a total of 12 experimental plots. In the experiment, the tomato growth rate of plant height and stem diameter, root growth characteristics, and leaf area index (LAI) were measured. And, the evaluation indices of photosynthesis, such as the chlorophyll and photosynthetic rate, were also determined. Additionally, the plant biomass, the tomato yield, irrigation amount and IWUE (irrigation water use efficiency) were also measured. The correlation of these indicators was used to explore internal interaction and to determine the best agronomic measures in greenhouse. The results showed that subsurface drip irrigation with drip pipes in 20 cm burial depth significantly increased the overall photosynthesis of tomato plant, promoted tomato root length, root area, and number of root branching, enhanced tomato yields by 22.35% compared with the CK, and had no significant difference on fruit soluble sugar and organic acid content with the CK, but significantly increased total soluble solids, soluble protein, VC (vitamin C), lycopene content, and sugar acid ratio by 10.86%, 32.34%, 35.66%, 33.97%, and 53.01% respectively compared with the CK, and improved water use efficiency that was 35.91% higher than CK (P<0.05). Subsurface drip irrigation with drip pipes in 30 cm burial depth significantly increased tomato dry matter, stem dry weight, leaf dry weight and tomato yields by 50.73%, 92.67%, 57.54% and 19.53% compared with the CK respectively, and had no significant difference on water use efficiency with subsurface drip irrigation with drip lines in 20 cm burial depth, however lowered tomato fruit quality. Therefore, subsurface drip irrigation with 20 cm burial depth is recommended to increase production, enhance fruits quality and improve water use efficiency to tomato production in a greenhouse.