Effect of different particle sizes of rice husk biochar on soil properties, nutrient leaching, and Brassica alboglabra productivity in sandy loam soil

Abstract

Soil health enhancement with biochar application is well documented. However, the influence of particle sizes of biochar coapplied with synthetic fertilizers on soil properties (physical, chemical, and biological), hydrological properties, nutrient leaching, and nutrient use efficiency are not well understood, particularly for sandy loam soil. There is still a knowledge gap regarding the effects of varying particle sizes of biochar on soil characteristics and the microbial community. Therefore, the influence of biochar particle size along with fertilizer was investigated in this study. We examined the short-term interactive effect of particle sizes of rice husk biochar (RHB) with fertilizer. For this study, RHB was produced at 300 to 550 o C using the traditional kiln method and was conducted at Naresuan University, Thailand. Morphology of RHB was classified using Field Emission Scanning Electron Microscope and element analysis by Energy Dispersive X-ray Spectrometer (FESEM-EDS). Three different sizes; of RHB: (i) less than 0.25 mm, (ii) 0.25 – 1 mm, and (iii) 1 – 2 mm were used to mix with the sandy loam soil, tested in the soil column, and sampled for four-time periods at 0, 8, 18, and 29 days after transplanting of Brassica alboglabra. Treated soils were analyzed for pH, electrical conductivity (EC), organic carbon (OC), total nitrogen, available phosphorus, and exchangeable potassium. BIOLOG EcoPlate was used to investigate the effect of biochar and fertilizer on soil microbial activity at harvesting time. Biochar amendment without fertilizers significantly increased soil pH and organic carbon but did not affect EC, while co-application with fertilizers significantly increased nutrient concentrations. The soil water and nutrient retention increased with decreasing biochar particle sizes. However, large size biochar decreased bulk density more significantly. The smallest biochar size (<0.25 mm) was 20% greater potential in leaching reduction as compared to the control. Besides, medium (0.25 – 1 mm) and large (1 – 2 mm) sizes of RHB reduced leaching by 11%, and 5%, respectively. Adding biochar (regardless of size) increased microbial activity in the metabolization of phenolic compounds. The large size of biochar (1-2 mm) provided the greatest microbial activity on carboxylic acids. Results suggest that biochar improved soil properties and reduced water and nutrient leaching, increase nutrient use efficiency and microbial diversity and activity, and the beneficial effects were enhanced when coapplied with fertilizer. No significant effect on Brassica alboglabra height and biomass was observed.

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