Biochar Improves Greenhouse Tomato Yield: Source–Sink Relations under Deficit Irrigation

Abstract

It is important to evaluate any effects that biochar may have on tomato yield under deficit-irrigation to develop water-saving and yield-increasing best management practices for greenhouse tomato production. For this purpose, greenhouse trials were conducted in 2021 and 2022 with five biochar (B) application rates and three irrigation (W) levels. The B treatments were B0: 0 t ha−1; B1: 15 t ha−1; B2: 30 t ha−1; B3: 45 t ha−1; and B4: 60 t ha−1, and the W levels were W1: 50–70% of field capacity (θf); W2: 60–80% of θf; and W3B0: 70–90% of θf full irrigation without biochar, which was designated as the control. Our objective was to quantify the effects of biochar on the characteristics of tomato sources and sinks to determine, first, the optimal irrigation–biochar combination to achieve high yield tomato production, and, second, evaluate the mechanisms of this effect. At W1 and W2 irrigation levels, the addition of 30–60 t ha−1 and 45–60 t ha−1 biochar could compensate for the adverse effects of deficit-irrigation on the tomato source and sink characteristics. Our results show that in both years the highest tomato yield was obtained with the W2 irrigation level and the B3 biochar application rate, with 52% higher tomato yield compared to the lowest value obtained with the W1 irrigation level and B0 application rate. We conclude that biochar application can improve tomato yield by promoting the filling rather than the building of the sink capacity. The tomato yield was mainly affected by the net photosynthetic rate (Pn), followed by the leaf area, and the leaf chlorophyll content indirectly affected tomato yield through Pn. The W2 irrigation level combined with the B3 biochar application rate resulted in the best water–biochar combination under the experimental conditions.