Response of yield and quality of greenhouse tomatoes to water and salt stresses and biochar addition in Northwest China

Improving productivity of saline soils under drought condition is critical for sustainable agricultural development in arid areas. Whether biochar addition can interact with drought and salinity on fruit yield and quality remains unclear. A pot study was conducted to examine the effects of water, salinity and biochar addition on tomato yield and quality in a solar greenhouse of northwest China. There were twelve treatments combining two irrigation levels of high (W1) and low irrigation (W2 = 2/3 W1), three salinity levels with 0%, 0.3% and 0.6% of soil dry weight salts, referred to S0, S1, and S2, respectively, and two biochar addition levels with 0 (B0) and 1% (B1) of soil dry weight. Biochar, water, salinity, and the interaction between water and salinity were found significant affecting yield and irrigation water productivity (IWP). Biochar addition reduced yield and IWP, ranging from by 7% of W2S0 to 43% of W1S2. The difference in yield and IWP between W1 and W2 was greater for lower salinity treatments. The reduction percentage of W2, relative to W1, was 70%, 38%, and 29% for yield, 58%, 14%, and 0.9% for IWP under S0, S1, and S2, respectively. The effects of water, salinity and biochar treatments was found inconsistent for different quality parameters. Adding biochar had no significant effect on firmness, and slightly increased total soluble solids (TSS) and Vitamin C (VC) at both irrigation levels, while lower irrigation and higher salinity generally led to higher TSS and VC. The absolute slope value of the linear regression of yield and quality parameters with soil electrical conductivity was smaller under W2, relative to W1, indicating that the salinity effect was less pronounced when water stress was greater. The results are valuable in developing and evaluating remedy measures for improving saline soil productivity in arid areas.