Effects of biochar amendment at various soil depths on maize roots and growth indices

Biochar application in the soil has shown its potential for improved plant growth, root structure, and nutrient availability. However, uncertainties remain regarding the optimal depth for biochar application and its interaction with roots, which significantly influence plant growth and development. This transparent rhizobox trial consists of five treatments: control treatment (T1) with recommended dose of fertilizer, and four biochar addition treatments with different depths viz. 5 (T2), 10 (T3), 15 (T4) and 20 cm (T5). FESEM, EDX-Spectroscopy was performed to elucidate the change in morphology and element distribution pattern of biochar after application in soil. Fresh biochar has 53.7% carbon and 19.9% oxygen, however, aged biochar shown 37.4% carbon and 36.4% oxygen content. The T5 exhibit the best outcomes, with the most significant increment in maize root traits over the control treatment (T1). In particular, T5 recorded a maximum improvement in root length (+ 48.2%), root volume (+ 42.7%) and root dry biomass (+ 56.7%) compared to the control treatment when biochar was applied at 20 cm soil depth. Shoot traits at 20 cm biochar incorporation revealed an increase in shoot fresh biomass (+ 23.1%), shoot dry biomass (+ 15%), leaf area (+ 50.5%) and number of leaves (+ 40.7%) as compared to the control treatment. As compared to the control, a considerable rise in soil nitrogen, phosphorus, and potassium was observed in biochar amendment at 20 cm depth, with the highest nitrogen in T5 (20.9%), phosphorus in T5 (103%), and the percentage increase in potassium in T5 (55.5%). One of the most consistently prevalent molecules examined by GC-MS was methyl stearate, a fatty acid ester detected in all five treatments. Methyl stearate content increased as the depth of biochar increased: T1 (10.26%), T2 (8.67%), T3 (12.40%), T4 (12.93%), and T5 (14.65%). Overall, the findings of this study suggest that uniform application of biochar in the top soil layer significantly enhances the above- and below-ground attributes of plants.