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

Abstract

Co-pyrolysis of animal manure biomass with bone meal (BM) and soaking of the resultant biochar in urea containing solutions may offer a sustainable and cheap way of formulating slow-release nitrogen (N) and phosphorus (P) fertilisers. This method can lead to optimisation of the carbon sequestration capacity of the biochar, abatement of environmental pollution by P and N and alleviation of the severity of the projected future scarcity of P. A few studies have indicated that sorption can create efficient slow-release fertilisers although all of them utilised charged moieties such as ammonium ions to formulate them and as a result, there is a paucity of data concerning the efficiency of fertilisers formulated using uncharged compounds like urea. It’s against that background that we examined the possibility of leveraging co-pyrolysis and sorption with urea containing solutions to formulate slow-release N and P fertilisers along with assessing the agronomic efficiency of the formulated fertilisers through cultivating lettuce in pots for two seasons. Both urea-hydrogen peroxide (UHP) and urea were utilised as N sources. UHP (CDBM-UHP) and urea (CDBM-Urea) containing biochars averagely released 64.40% and 87.00% of the added N, respectively over the 28-day incubation period with the amount of N released decreasing with increasing concentrations of BM in the biochar. Lettuce yields and nutrient use efficiencies of N and P were higher in the CDBM-UHP than in the CDBM-Urea treatments. It’s therefore clear that sorption of UHP by BM containing biochar concomitantly slows-down releases of N and P and boosts the agronomic efficiency of the fertilisers.

Nutrient Dynamics in Sandy Soil and Leaf Lettuce Following the Application of Urea and Urea-Hydrogen Peroxide Impregnated Co-Pyrolyzed Animal Manure and Bone Meal

“…The soil used had the following characteristics; pH (CaCl 2 ) = 5.56 ± 0.21, Total N (%) = 0.12 ± 0.05, Ca (g/kg) = 1.064 ± 0.17, K (g/kg) = 0.09 ± 0.01, Mg (g/kg) = 0.06 ± 0.02, Olsen P (ppm) = 19.87 ± 2.89, B (ppm) = 6.72 ± 0.98, Mo (ppm) = 0.23 ± 0.07, Zn (ppm) = 43.59 ± 7.17. The chemical properties of the BM biochars and their corresponding NEBs fertilizers can be found in Luyima et al [7]…”

“…The urea-enriched biochars were produced as outlined by Luyima et al [7]. Briefly, cow dung was dried and strained through a 2 mm sieve, after which bone meal was added and mixed thoroughly.…”

“…Lammel et al [5] for example, indicated that most common polymer-coated fertilizers are about 8-12 fold more expensive than the conventional mineral fertilizers. Additionally, some of the coating materials used in the formulation of the slow release fertilizers are non-biodegradable, while others are mutagenic and/or carcinogenic [4,6,7]. Because of the issues mentioned above, a lot of research effort has been geared towards exploring environmentally friendly and cost-effective carriers and coating materials for the plant nutrients [4].…”

“…It is against this background that [12] proposed the usage of bone waste and discerned that the biochar obtained from the co-pyrolysis of cow dung and bone meal retained much more carbon than the pristine cow dung biochar. Apart from increasing the amount of carbon (C) retained in the biochar, co-pyrolysis of biomass with P also slows down the rate of discharge of P and it is thus an effective way of formulating a slow release P fertilizer as confirmed by Zhao et al [13] and Luyima et al [7]. It is worthy to note, however, that adsorption is a crucial mechanism in the preparation of slow release fertilizers [4], which may explain why the vast majority of the biocharbased fertilizers have been formulated with salts containing charged elements such as ammonium, nitrate, phosphates, K, etc.…”

“…It is against this backdrop that our previous studies, i.e., Luyima et al [7,12] proposed an easy way of formulating slow release of nitrogen and P through co-pyrolysis of cow dung (a representative of animal manure) with bone meal and sorption of the biochar in urea and urea-hydrogen peroxide solutions. The formulated urea-enriched biochars were efficient at reducing ammonia emissions as well as lessening N and P releases and boosting agronomic efficiency.…”