Comprehensive evaluation of effects of various carbon-rich amendments on tomato production under continuous saline water irrigation: Overall soil quality, plant nutrient uptake, crop yields and fruit quality

Since freshwater shortage is common in most regions of the world, saline water has been used to irrigate a wide range of crop species. However, continuous saline water irrigation can easily lead to soil degradation and reductions in crop yields. In this study, we measured the effects of various carbon-rich amendments (CRAs) on soil quality, plant nutrient uptake , crop yields and tomato quality under continuous saline water irrigation. The treatments considered were (i) untreated soils irrigated with freshwater (control), (ii) untreated soils irrigated with saline water (SW), (iii) soils treated with straw-C and irrigated with saline water (SW+SC), (iv) soils treated with biochar-C and irrigated with saline water (SW+BC), (v) soils treated with nano-C and irrigated with saline water (SW+NC), and (vi) soils treated with composted straw-C and irrigated with saline water (SW+CC). Soil quality was comprehensively evaluated using a soil quality index (SQI) covering a wide range of physicochemical and microbial properties. In general, continuous saline water irrigation resulted in adverse effects on soil quality (e.g. enhanced sodium adsorption ratio, reduced nutrient availability and decreased microbial activities/functions) and tomato growth (e.g. the reduction of plant biomass and fruit yield). However, these adverse effects were efficiently alleviated by the application of CRAs. Specifically, all four CRAs increased SQI under continuous saline water irrigation. There were significantly ( p < 0.001) and positively relationships between SQI and crop productivity (e.g. fruit yield and plant biomass). The application of straw-C or nano-C mainly increased crop yields, while the application of biochar-C or composted straw-C primarily improved fruit quality. Overall, the application of straw-C resulted in not only the highest SQI but also the highest fruit yield, while the application of biochar-C strongly enhanced overall fruit quality under continuous saline water irrigation. • Continuous saline water (SW) irrigation resulted in serious soil degradation. • Carbon-rich amendments (CRAs) improved soil quality under SW irrigation. • Straw-C and nano-C mainly increased crop yields under SW irrigation. • Biochar-C and composted straw-C primarily improved fruit quality. • Straw-C showed the highest soil quality as well as the highest fruit yield.