Increasing soil organic matter and short-term nitrogen availability by combining ramial chipped wood with a crop rotation starting with sweet potato

Abstract

Increasing soil organic matter is essential for enhancing agricultural soil quality and ecosystem services, including crop yields. Ramial chipped wood (RCW), a pruning by-product, has great potential in this regard, yet its short-term effects on soil organic carbon (C) retention, nitrogen (N) availability, and crop yields remain unclear. This study aimed to rapidly increase soil organic matter and nutrient stocks by applying RCW combined with sweet potato, a starter crop suitable for low-nutrient soils. We monitored soil organic C and N stocks, crop yields, and N use in soils recently enriched with high or low doses of RCW, comparing them to organically managed soils that were regularly tilled and fertilized with either organic granulate or plant residue compost. For the first time, we show that RCW application rapidly increased N stocks in the fine earth fraction, particularly at the high dose. At two months in high-dose plots, 61 % of the remaining C was retained in the organic debris fraction, while 73 % of N was incorporated into the fine earth. After one year, 22 % of the added C was retained in soil with the high RCW dose, whereas neither the low dose nor compost application led to significant C increases. In contrast, N retention was nearly 100 % for both RCW doses and compost. Agronomic production and crop performance were maintained or slightly improved with the high RCW dose, suggesting that the increased N stocks supported crop nutrition. Additionally, RCW enhanced biological N fixation in sweet potato. These results indicate that high-dose RCW incorporation into soils with sweet potato cultivation is a promising catalytic strategy to boost soil organic matter and N reservoirs while achieving good crop yields. This practice also promotes a circular economy by repurposing a locally available C-rich resource and aligns with sustainable agriculture principles.