Long term co‐application of biochar and fertilizer could increase soybean yield under continuous cropping: Insights from photosynthetic physiology

Background

Photosynthesis is the key to crop yield. The effect of biochar on photosynthetic physiology and soybean yield under continuous cropping is unclear. We conducted a long‐term field experiment to investigate the effects of co‐application of biochar and fertilizer (BCAF) on these parameters. Five treatments were established: F2 (fertilizer), B1F1 (3 t·hm^‐2 biochar plus fertilizer), B1F2 (3 t·hm^‐2 biochar plus reduced fertilizer), B2F1 (6 t·hm^‐2 biochar plus fertilizer), and B2F2 (6 t·hm^‐2 biochar plus reduced fertilizer).

Results

BCAF increased chlorophyll and leaf area, enhancing soybean photosynthesis. The net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), water use efficiency (WUE) and intercellular CO₂ concentration (C_i) were enhanced by BCAF. In addition, BCAF improved soybean Photosystem II (PSII) photosynthetic performance, driving force, potential photochemical efficiency (F_v/F₀), and quantum yield of electron transfer (φ_E0). Furthermore, BCAF enhanced the accumulation of photosynthetic products, such as soluble proteins, soluble sugars and sucrose content, resulting in higher leaf dry weight. Consequently, BCAF increased the soybean yield, with the highest increase of 41.54% in B2F1. The correlation analysis revealed positive relationships between soybean yield and chlorophyll, leaf area, maximal quantum yield of PSII(F_v/F_m), electron transport fux per cross section at t=0 (ET₀/CS₀), trapped energy fux per cross section at t=0 (TR₀/CS₀), composite blade driving force (DF_Total), and leaf dry weight.

Conclusions

We demonstrated that long‐term BCAF enhances soybean photosynthesis under continuous planting, reduces fertilizer use and increases yield. This study reveales a novel way and theory to sustainably increase soybean productivity.

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