Impact of combined application of biochar and phosphorus on maize production and soil properties in Yellow River Delta: a comparison between contrasting climatic conditions

Yellow River Delta’s arable land had great potential for grain production if reasonable agronomic measures were taken. To date, the question of whether and how biochar (C) and phosphorus (P) addition jointly regulates maize production in this area remains unclear. Consequently, a two-year (2021–2022, with contrasting climatic conditions) field experiment including three biochar intensities ((0 (C ₀ ), 5000 (C ₁ ), and 10000 (C ₂ ) kg ha ^− 1 )), three phosphorus fertilization levels (0 (P ₀ ), 100 (P ₁ ), and 200 (P ₂ ) kg P ₂ O ₅ ha ^− 1 ), and their combinations was conducted in Wudi, Shandong province, China. Across the two-year study, C rather than P addition exerted a significantly positive impact on maize yield, yield component parameters, and nutrient (nitrogen (N) and P) accumulation ( P  < 0.01). Separately for the two years, maize growth and nutrient uptake under unfavorable weather conditions (excessive rainfall) of 2021 were all obviously depressed ( P  < 0.01) relative to 2022, while these stimulated magnitudes by C in 2021 became more marked than in 2022. Correspondingly, C addition enhanced a greater proportion of dry matter and nutrient remobilization in 2021. On the other hand, soil physical and chemical properties were mostly improved by C addition, in which the increased extent of hydraulic conductivity ( Ks ) was much more dramatic. Taken together, these plant and soil mechanisms could alleviate the adverse effect induced by heavy-rainfall weather conditions on crop shoot and root, respectively, and explain the higher promotion effect of C addition on maize yield in 2021 than in 2022. More importantly, negative interactions of C×P on soil available P and phosphorus activation coefficient (PAC) ( P  < 0.01) were captured, which might contribute to the lack of synergistic effects of C×P on maize growth. These results suggested that C addition could enhance maize production and ensure crop yield stability if facing severe weather conditions; while the combined incorporation of this kind of C and P we used (especially high-amount addition treatment of C ₂ P ₂ ) was not recommended, and other types of biochar accompanied with P fertilizer needed to be tested in the Yellow River Delta. Overall, the present study delivered useful insight into the sustainable utilization of C and P fertilizer in saline-alkali soils.