Study on the optimal water−biochar management mode based on pan evaporation for solar greenhouse tomato (Solanum lycopersicum L.) in Northeast China

Biochar is commonly employed to enhance soil structure. However, the soil structure degradation due to multi-year continuous cropping poses a significant obstacle to the advancement of solar greenhouse agriculture. This study aimed to optimize the water−biochar management mode for seasonal solar greenhouse tomatoes (Solanum lycopersicum L.), which have been continuously cultivated over three years, with irrigation guided by the evaporation of a 20 cm evaporation pan (Ep-20). The experimental design employed a split–plot arrangement with two factors. The primary factor, irrigation amount, was tested at three levels: 0.6 Ep-20 (W1), 0.8 Ep-20 (W2), and 1.0 Ep-20 (W3). The secondary factor, biochar amount, was tested at three levels: 0 (B0), 20 t ha−1 (B1), and 40 t ha−1 (B2). The results revealed that biochar reduced soil bulk density and enhanced field capacity, tomato plant height, and photosynthesis. Increased irrigation improved tomato appearance quality but reduced nutritional quality, whereas higher biochar application improved both aspects. Principal component analysis (PCA) and grey relational analysis (GRA) results identified W2B2 as the optimal mode for the quality of spring tomato and autumn tomato. Compared to the control (W3B0), W2B2 exhibited an average increase of 18.0 % in yield and 47.5 % in irrigation water productivity (WPI) with a 20 % reduction in irrigation amount across two seasons. The technique for order preference by similarity to ideal solution (TOPSIS) comprehensive evaluation determined that the W2B2 mode maximized comprehensive benefits, enhancing both the overall quality of tomato and achieving higher yield and WPI. This study utilized the Ep-20 to characterize the reference crop evapotranspiration (ETo) and the crop evapotranspiration (ETc). The investigation demonstrated the feasibility of utilizing Ep-20 to guide irrigation under biochar application conditions and develop ETc estimation models for water−biochar management modes to optimize solar greenhouse tomato production.