Effects of reducing water and fertilizer rates on soil moistureand yield and quality of tomato in solar greenhouse

【Objectives】Fertigation technology has a great potential to replace the traditional irrigation and fertilization methods in the protected cultivation in China.Soils, climate, and crops require different frequency of irrigation and fertilization. Therefore, effects of different water and nutrient treatmentson soil moisture, nutrient uptake, yield and quality of autumn-winter tomato in Guanzhong Plain, Shaanxi was studied. Our aim was to setup the optimum rates of irrigation and fertilization in solar greenhouses. 【Methods】 The field trial included three treatments, the conventional treatment (CK) in which irrigation rate equaled to 100% evapotranspiration and average rates of fertilizers used by local farmers were applied (conventional fertilizer treatment), and reducing 20% and 40% of water and fertilizer rates in comparison with CK (S1 and S2). The fertilizers were added into the irrigation system with Venturi tube during the crop growth. Soil moisture in 0-20 cm and 20-50 cm layers was continuously monitored by an automatic tension meter system (Skye DataHog2, UK). Soil water content was calculated with soil water characteristic curve. water surface evaporation was determined with the evaporating dish method (diameter 20 cm), and its relationship with loss of soil available water was analyzed. The nutrient absorption, yield, quality, irrigation utilization of autumn-winter tomato in different treatments were also determined. 【Results】 1) The soil relative water contents are higher 75% in 0-50 cm soil layer in all the treatments throughout the whole growing period of tomato, indicating soil water supply is adequate for tomato growth. The soil water contents in 0-20 cm and 20-50 cm soil layers in the conventional treatment reach or exceed the field capacity after irrigation, which indicates that water infiltrated below 50 cm soil layer and would result in nutrient leaching. Compared with CK, the soil relative water contents in the treatment of reducing 40% of water and fertilizer rates are mainly in optimum range from 75% to 85%. 3)When reducing the irrigation rate, the water loss from 0-50 cm soil layer is decreased, and the loss of effective storage water equals 65.4% of the canopy water evaporation, and also equals to the irrigation amount in the S2 treatment. 3)There are not significant differences in nutrient absorption, yield and quality of tomato among the different treatments. However, the use efficiency of irrigation water is increased from 55.1 kg/m3 in the conventional treatment to 83.2 kg/m3 in the water and nutrient saving treatments. 【Conclusions】 The optimum irrigation rate for the solar greenhouse in the study region is 65% of water surface evaporation. The appropriate irrigation quota for the autumn-winter tomato in solar greenhouse is 1057 m3/ha, the irrigation amounts in August, September, October, November and December are 168, 169, 132, 105, and 50 m3/ha, respectively, and the time intervals of irrigation in August, September, October, and November are 20-30 days, 8-13 days, 8-13 days, and 20-30 days, respectively and the irrigation in December is dependent on climate, either less rate or no irrigation. No irrigation is needed in January.