Effects of waterweed compost derived from Lake Biwa on Komatsuna (Brassica rapa var. perviridis) growth

ABSTRACT In Lake Biwa, located in Shiga Prefecture, Japan, the overgrowth of waterweeds has become a significant environmental and human-life problem. Therefore, the waterweeds are systematically harvested and composted. In order to consider the effective use of waterweed compost for carbon neutrality and resource recycling, we clarified the characteristics of the waterweed compost by cultivation experiments with Komatsuna (Brassica rapa var. perviridis). When the waterweed compost (20%) was applied alone, the growth of plants was promoted about 1.7 times compared to a control containing the same amount of fertilizer components. However, the plant showed yellowing of leaves and a high C/N ratio, indicating obvious symptoms of nitrogen deficiency. The application of the waterweed compost (20%) with chemical fertilizer remarkably enhanced plant growth up to about 3.5 times without nitrogen deficiency compared to a control containing only chemical fertilizer. Interestingly, the coexistence of the waterweed compost and chemical fertilizer activated nitrification and diversified soil bacteria (Chao1 index, 213.0; Shannon index, 6.50) rather than the waterweed compost alone (Chao1 index, 41.3; Shannon index, 4.34). Our results indicate that the waterweed compost functions effectively as an organic fertilizer and a soil amendment, contributing to sustainable agriculture. GRAPHICAL ABSTRACT