Effects of sugarcane substrate inputs on microbial biomass and nitrogen availability in tropical sandy soils of northeast Thailand
2021
Chuwongpanich, Walaiphan | Fujii, Kazumichi | Inagaki, Yoshiyuki | Hayakawa, Chie | Chittamart, Natthapol
The increasing demand for sugarcane residue to produce industrial biofuels competes with organic-matter inputs to tropical soils for increasing fertility. Soil nitrogen (N) availability to plants and carbon (C) storage can be optimized by the selection of substrate types and quantities. We tested whether substrate-induced microbial growth increases soil N mineralization and C stabilization as substrate inputs increase. The effects of substrate additions (cane sugar, leaf litter, and humic acid extracted from filter cake) on microbial growth and N availability were studied using C3/C4 plant C isotopic signatures in a sandy soil of northeast Thailand. The initial growth of microbial biomass in cane sugar-amended soil caused a short-term flush of N derived from the native soil organic matter within 3 days, whereas in the soils amended with leaf litter or humic acid, N was retained in microbial biomass or dissolved organic matter, respectively. Net mineralization of the native soil organic N was maximized by sugar addition at a dosage corresponding to 10 folds of microbial biomass-C. The efficacy of substrates stabilized in the heavy density fraction (>1.6 g cm⁻³) followed the order: leaf litter > humic acid > sugar. Soil net N mineralization can be promoted by sugar inputs (e.g., bud node) at an early growth stage, while leaf litter and humic acid inputs can increase C storage efficiently in the sandy soil without increasing risks of N starvation and loss when they are applied at several tons of C per hectare at least 3 weeks before planting.
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