Influences of continuous wood-derived biochar application on soil chemical properties and lettuce (Lactuca sativa L.) yield

Abstract

Biochar application to agricultural soil has been widely conducted to improve C stock and fertility of the soil, contributing to enhancement of crop productivity. However, the impact of biochar application can vary with its specific characteristics and application rate. This study was performed to investigate the effects of wood-derived biochar (WB) application on soil properties and yield and quality of lettuce through two-season pot experiments, with the ultimate goal of identifying the most effective application rate. The biochar treatments were composed as follows based on the recommended application rate (2 Mg ha-1): 0% (control), 50% (WB100), 100% (WB200), 200% (WB400), and 400% (WB800). Lettuce plants were grown in two consecutive monocultures in 2023, and the WB was applied before planting each time. Among soil parameters, pH, organic matter content, and available P tended to increase as the WB application rate increased. Through the two-season treatment of WB800, soil pH increased from 7.1 (control) to 7.4, and organic matter and available P contents also increased by 29% (61 to 79 mg kg-1) and 32% (19 to 25 g kg-1), respectively, compared to control. After the second cultivation, the highest fresh weight (FW) of lettuce was observed in the WB200 treatment (51 g pot-1), which was significantly higher (ca. 65%) than in the control (31 g pot-1). In addition, nutrient uptake, such as N, P, K, Ca, and Mg, in the plant after the 2nd cultivation were highest in the WB200 treatment, while the WB800 treatment represented the lowest values. Polynomial regression analysis suggested that the optimal application rate of WB for maximum yield ranged between 3.04 and 3.36 Mg ha-1. Our findings indicated that the WB application could lead to a significant effect for growing lettuce plants but vary with the application doses and times. Further long-term researches are needed to maximize the effectiveness of WB applications for soil management and cropping.