Effects of moistube depth and density on tomato yield and quality in solar greenhouse

Tomato (Solanum lycopersicum Mill.) is one of the vegetables widely cultivated in solar greenhouses in North China. As irrigation is the main source of soil moisture in solar greenhouse, it is very important to select appropriate irrigation methods and technical parameters to improve agricultural production, keep greenhouse air humidity, and reduce the incidence of pests and diseases. Moistube irrigation is a new underground irrigation technology with semi-permeable membrane as the core material which provides water to crop root zone soils in a slow and continuous flow. The advantages of this new irrigation technology include energy saving, low operation cost, easy operation, good anti-clogging performance, less deep leakage, etc. However, this technology is still in experimental stage and therefore has not been applied at large scale, and some important parameters needed to be optimized. In this experiment, drip irrigation with mulch was used as control to explore suitable technical parameters of moistube irrigation in solar greenhouse conditions. Three depths (10, 20, 30 cm) and three densities (one, two and three moistubes with two lines of tomatoes in one planting ridge, respectively expresses as 1 tube with 2 lines, 2 tubes with 2 lines, 3 tubes with 2 lines) were set up to study the effect of different depths and densities of moistube on the growth, yield and quality of tomato in solar greenhouse conditions. The experiment was done from October 2015 through April 2016 in a 108 m by 8 m solar greenhouse (108°02′E, 34°17′N) in Yangling Agricultural Hi-tech Industries Demonstration Zone, Shaanxi Province, China. The results showed that moistube irrigation enhanced the growth of tomato compared with the drip irrigation with mulch. Compared with control, moistube irrigation increased fruit diameter, weight, volume, total yield and irrigation water use efficiency by 8.58%, 11.99%, 18.79%, 60.93% and 103.40%, respectively. Our results suggested that water-saving under moistube irrigation conditions was as high as 37.73%. For tomato quality, compared with control, the contents of vitamin C, soluble sugar and sugar-acid ratio also increased under moistube irrigation, with average increasing rates of 27.07%, 4.48% and 21.38%, respectively. In terms of comprehensive quality of tomato, the moistube depth was in the order of 30 cm > 10 cm > 20 cm under the same moistube density, the moistube density was in order of 1 tube with 2 lines > 2 tubes with 2 lines > 3 tubes with 2 lines under the same moistube depth. In general, plant height, stem diameter, fruit shape and total yield of tomato decreased with increasing moistube depth. These parameters also increased with increasing moistube density. However, stem diameter and irrigation water use efficiency decreased with increasing moistube density. Based on total yield, irrigation water use efficiency and quality of tomato and the economic cost of moistube and other factors, 10 cm depth and 1 tube with 2 lines (with total tomato yield of 87.38 t.hm^-2, irrigation water use efficiency of 108.91 kg.m^-3, and third in comprehensive quality rank) were the most suitable technical parameters for moistube irrigation in solar greenhouse condition.