Wheat straw biochar amendment significantly reduces nutrient leaching and increases green pepper yield in a less fertile soil

Declining soil fertility and inefficient water and nutrient use pose a growing challenge to increasing agricultural production to meet growing global food demand. As a soil amendment, biochar can potentially serve in addressing these issues; however, its impacts on nutrient leaching from soils of different pre-existing fertility levels are poorly understood. A potted green pepper (Capsicum annuum L. var. Red Night) production system, arranged in a randomized complete block design, imposed two soil fertility management approaches (‘fertile’: standard soil + [N:P:K (kg ha ⁻¹) 140:165:160] vs. ‘less fertile soil’: 1:1 standard soil: sand, [N:P:K (kg ha ⁻¹) 140:190:240], factorially combined with three levels of wheat straw biochar amendment [0%, 1%, and 3% (w/w)]. Biochar treatment effects on nutrient leaching (NO₃⁻-N and PO₄³⁻-P) and plant yield were assessed for each soil fertility management approach. Across soil fertility types, biochar amendments (vs. the lack thereof) significantly decreased (p≤0.05) leachate volume (68%–91%) and cumulative NO₃⁻-N (78%–93%) and PO₄³⁻-P (80%–99%) losses, whereas NO₃⁻-N, and PO₄³⁻-P concentrations in the leachate were only significantly reduced (p≤ 0.05) under the 3% biochar amendment. Pepper marketable yield in the less fertile soil was significantly (40%, p≤0.05) greater under the 3% biochar amendment than the non-amended treatment; however, no such difference existed in the fertile soil given its initially high soil nutrient levels. While farmers can amend soils with biochar to reduce nutrient leaching, its impact on plant productivity will depend on the rate of amendment.