Nutritional Effects of Liquid Digestate on Tomatoes Grown in Facility Substrates

The nutritional effects of liquid digestate on tomatoes in facility soilless cultivation were investigated, so as to provide scientific basis for the substrate cultivation application of biogas slurry.

Here, tomato was used as subject, and the dual inputs of fertilizers (liquid digestate (D) and mineral fertilizer (M)) and soilless substrates (peat substrate (P) and cinder substrate (C)) consisted of four treatments. The parameters of tomato growth, photosynthesis and nutrients uptake were recorded during the experimental period, as well as the properties of substrates.

The tomato dry biomass under DP treatment was higher than that under MP treatment by 12.6%, and DC treatment was higher than MC treatment by 70.9%. However, the dry biomass under DP and MP treatments were significantly higher than that under DC and MC treatments (P<0.05). The Cond, Ci and Tr of tomato leaf under DP treatment was significantly higher than that under other treatments (P<0.05), and the greatest leaf photosynthetic rate was also observed under DP treatment of (18.17±0.47) µmol·m^-2·s^-1. Liquid digestate significantly increased the dry biomass and photosynthesis of tomato plants. The total N and total P content of plant under DP treatment were higher than that under MP treatment by 46.9% and 19.7%, respectively, and DC treatment were 1.38 and 2.45 times higher than MC treatment, respectively. Moreover, liquid digestate treatments significantly increased the pH value, organic matter and available phosphate content of substrates compared with chemical fertilizer treatments (P<0.05). The highest fruit yield was obtained under DP treatment of (6.0±0.4) kg·m^-2, and the yields between DP and MP treatments had no significant difference. The liquid digestate treatments could significantly increase the soluble sugar content and vitamin C content in tomato fruits (P<0.05), and improve fruit quality. Meanwhile, the results of principal component analysis showed that DP treatment had the best overall performance, followed by MP and DC treatments, while MC treatment was the worst.

The application of liquid digestate into peat substrate increased the photosynthetic efficiency of leaves and the absorption of nitrogen and phosphorus of tomato plants, as well as the properties of substrate and the yield and quality of fruits. Therefore, the combination was recommended for use in facility tomato cultivation.