Effects of lignite bioorganic product on sunflower growth, water and nitrogen productivity in saline-sodic farmlands at Northwest China

Abstract

Continuous applications of lignite bioorganic fertilizer (LBF) to the field have achieved substantial improvements in soil physicochemical properties and crop yields in multiple regions throughout China. However, the effects of LBF on crop growth, and water and fertilizer productivity in saline-sodic farmlands were scarcely understood. Thus, in this study, a two-year field experiment with six treatments including a control treatment without any organic fertilizer (CK), a treatment amended with 21 t ha−1sheep manure (SM), and four treatments amended with 1.5 (LBF1), 3 (LBF2), 4.5 (LBF3), and 7.5 t ha−1 (LBF4) LBF, was conducted in 2019 and 2020 in the Hetao Irrigation District (HID), an area known for its saline-sodic conditions located at the upper Yellow River basin, China. The results showed that the LBF2 and LBF3 treatments improved plant height, leaf area index, and dry biomass by 8–76.7 cm, 0.3–2.4, and 309–402 g plant−1, respectively, in comparison with the CK treatment. The root length, root surface area, and root volume in the LBF2 and LBF3 treatment was 18.3–99.7 m, 464.6–2022.6 cm2, and 7.6–46.4 cm3 larger than that in the CK treatment, respectively. Average yield, water productivity, partial nitrogen productivity, and economical gain in the LBF treatments were up to 2.2 t ha−1, 0.4 kg m−3, 23.6 kg kg−1, and 6100 Chinese Yuan ha−1, respectively, substantially higher than those of the CK treatment. In addition, compared with SM treatment, the LBF2 and LBF3 treatments also significantly improved sunflower growth and water and nitrogen productivity. The results of structural equation model analysis and linear regression analysis showed that LBF2 and LBF3 treatments improved sunflower root growth mainly through improving absorption of soil nitrogen. Furthermore, the root indices had a significant positive relation with the sunflower yield, water productivity, and partial nitrogen productivity. The partial nitrogen productivity, water productivity, yield, and economic profits showed a quadratic relationship with the application rate of LBF. A comprehensive assessment of the partial nitrogen productivity, water productivity, yield, and cost versus economic suggested that an application rate of 3.0–4.0 t ha−1 of the lignite bioorganic fertilizer is optimal for achieving a sustainable improvement of crop yield, water productivity, and partial nitrogen productivity in saline-sodic farmlands.