Impacts of Vetiver Grass and DT2008 Soybean Cover Crop Practices on Soil Quality in Citrus Orchards in Cao Phong, Hoa Binh

This study investigated the efficiency of biomass management, residue quantity, and quality from Vetiver grass and DT2008 soybean cover crops in improving soil quality, including carbon and nitrogen content and soil physiochemical properties. Mesocosm experiments in pots were conducted with six treatments, each was replicated three times: CT0 (control), CT1 (2% Vetiver grass mulch), CT2 (2% DT2008 mulch), CT3 (1% Vetiver grass and 1% DT2008 mulch), CT4 (1% Vetiver grass and 1% DT2008 buried), and CT5 (2% DT2008 buried). After 12 months, significant increases in total carbon, nitrogen, and humic and fulvic acids were observed, indicating enhanced soil physiochemical properties. CT5 and CT4 showed the highest carbon, nitrogen, and cation exchange capacity (CEC) improvements. Soil moisture, pH in water (pHH2O), pH in KCl (pHKCl), and hydrolytic acidity were higher in CT1, CT2, and CT3. Nitrogen accumulation efficiency was relatively lower than carbon (24.44% to 86.67%), while carbon accumulation efficiency was much higher (41.94% to 91.72%). The most effective methods were to bury soybean biomass or mulch Vetiver grass over a soybean plant mulching layer, with Vetiver grass mulch recommended for enhancing and conserving soil fertility.