A Biochar-Based Route for Environmentally Friendly Controlled Release of Nitrogen: Urea-Loaded Biochar and Bentonite Composite

Abstract

Biochar-based fertilizers have attracted increased attention, because biochar can improve the soil fertility, promote plant growth and crop yield. However, biochar-based controlled release nitrogen fertilizers (BCRNFs) still face problems because of the high cost, inefficient production technology, instability of nitrides, and the challenge associated with the controlled release of nutrients. In this study, we hydrothermally synthesised novel BCRNFs using urea-loaded biochar, bentonite and polyvinyl alcohol for controlled release of nutrients. Scanning electron microscopy and gas adsorption were conducted to identify the urea-loading and storage of bentonite in the inner pores of the biochar particles. X-ray diffraction, Fourier transform infrared spectroscopic and X-ray photoelectron spectroscopic studies demonstrated that strengthening the interactions among biochar, urea, and bentonite, helps control the moisture diffusion and penetration of bentonite, thereby leading to nutrient retention. The BCRNF showed significantly improved nutrient release characteristic compared with that of a mixture of biochar and urea. This urea-bentonite composite loaded with urea provides control over the release of nutrients stored in the biochar. BCRNF, especially those produced hydrothermally, can have potential applications in sustainable food security and green agriculture.

Sorption of urea hydrogen peroxide by co-pyrolysed bone meal and cow dung slowed-down phosphorus and nitrogen releases but boosted agronomic efficiency

“…Even though research into BFs is still in a fledgling state, the few available studies overwhelmingly substantiate the slow release capabilities of the fertilisers with the level of efficiency of the slow release capacities heavily dependent on the preparation methods used. For example, Liu et al [15] indicated that a fertiliser produced by mixing biochar and urea through grinding slowed N release by less than 10% in the first 28 days of the experiment while formulating the same mixture under a sealed reactor led to a slight increase in the slow release capacity of the resultant fertiliser. Additionally, halving the urea concentration while doubling the biochar content and adding bentonite to the mixture in the sealed reactor produced a fertiliser that released only 86.7% of N which accentuated an improvement in the slow release potential of the produced fertiliser.…”

“…The results of the Liu et al [15] experiment demonstrate therefore, that mere mixing of biochar with urea has little impact on slowing N release and that more means of improving urea absorptivity into biochar should be explored if the slow release potentials of the generated fertilisers are to be maximised. Basing on that line of thought, it's surprising that mere soaking of biochar in UHP solutions undertaken in the current study produced more efficient slow release N fertilisers than the hydrothermal decomposition route espoused by Liu et al [15].…”

“…The results of the Liu et al [15] experiment demonstrate therefore, that mere mixing of biochar with urea has little impact on slowing N release and that more means of improving urea absorptivity into biochar should be explored if the slow release potentials of the generated fertilisers are to be maximised. Basing on that line of thought, it's surprising that mere soaking of biochar in UHP solutions undertaken in the current study produced more efficient slow release N fertilisers than the hydrothermal decomposition route espoused by Liu et al [15]. This is because the most effective slow release fertiliser of CDBM 2-UHP in the current study contained more urea (16.67%) than the most effective fertiliser formulated by Liu et al [15] whose urea content amounted to only 7.4%, but the former cumulatively released only about 58.65% of the added N while the cumulative N released by the latter stood at 61.3% over the same 28-day experimental period.…”

“…Pyrolysis, if leveraged can sustainably solve the abovementioned problems both through shrinking the volumes of the generated animal wastes and more importantly by providing cheap carrier and coating materials for plant nutrient elements in form of biochar, hydrochar and biooil which have great capacities to lessen nutrient releases into the environment. The potentialities and or efficacies of different products of pyrolysis in slowing-down releases of plant nutrients especially nitrogen have been widely assessed by several studies which include amongst others Chen et al [12], Punga et al [13], Ye et al [14] and Liu et al [15]. The results from all those studies confirm that products of pyrolysis are efficient in slowing down the release of easily leachable plant nutrient elements with resultant benefits for environmental quality and agricultural productivity.…”

Biochar Effect on Nutrients Availability to Barley

“…Release of the nutrients adsorbed by biochar could be the reason of a higher dry biomass yield in EB treatment. For example, Liu et al (2019) in their experiment with urea-enriched biochar found a 61-98% release of nitrogen from biochar to the soil through dissolution and diffusion processes.…”