Biochar as Influenced by Feedstock Variability: Implications and Opportunities for Phosphorus Management

Abstract

Agricultural wastes from plant and animal operations are often land applied to recycle and manage residues. Compositional variability among these wastes is vast. Some waste components can potentially represent a threat to the environment and humans depending on their nature, application loads, and soil type. Biochar, the product obtained by biomass heating under oxygen-limited conditions, has the potential to minimize risks associated with waste characteristics while promoting soil health. However, variation in the residue wastes (feedstocks) used to produce biochar carries over to the resultant biochar. In this study, we compare the chemistry and composition of biochars representing two broadly defined sources-animal (poultry litter, biosolids) and plant (mixed hardwoods, pure maple, pine)-and highlight phosphorus (P) management implications and opportunities presented by the variability among them. We also evaluate P leaching patterns of four selected biochars (poultry litter, biosolids, hardwoods, and maple) as applied at an identical rate (1% w/w) to two soils differing in P retention capacities. Cumulative P release following poultry litter biochar application and 20 leaching events was much lower for the more P retentive soil. Total P release from biochar-amended soils did not differ between soils when biochar from biosolids or from plant sources were used as the soil amendment. However, the biosolids-biochar released higher levels of P initially from the Candler compared with the Apopka (more P retentive than the Candler) soils, similar to that of poultry litter biochar. Compositional variations in feedstocks and resultant biochars must be understood in order to judiciously use them as crop nutrient amendments. There is potential to minimize nutrient deficiencies and environmental liabilities of biochars by matching feedstocks, or mixtures of feedstocks, to the needs of specific crops, and by considering the P retentive capacity of the soil where the biochar is applied.

Characterization of bonechar as a soil amendment in tropical soils

“…Compared to different types of biochars, bonechar had high total P, while the plant available P (M3-P) in the bonechar, was higher (2,800 mg kg -1 ) than plant-based biochars with M3-P <480 mg kg -1 , although lower than animal-based biochars (>7,000 mg kg -1 ). 9 The high M3-P concentrations in the bonechar suggests that the material could be a good P fertilizer source. Warren et al 8 indicated that the bonechar P solubility was intermediate between Gafsa phosphate rock and triple superphosphate fertilizer.…”

“…The chemical analyses included total P and Mehlich 3 (M3)-extractable K, Ca, Mg, Zn, Si, Na, Mn, Cu, Fe, Al, B, Cd, Ni and Pb. Details of the methodology are available in Freitas et al 9…”

“…8 Bonechar has some similarities with biochar produced from a variety of other feedstocks (e.g., manure, biosolids, and woody material). 9 Biochar has received great attention in the past decade for its potential to be used as a soil amendment and as a strategy for mitigating climate change. 10 In general, compared to biochar, bonechar has a lower carbon content.…”

Static and Dynamic Investigations on Leaching/Retention of Nutrients from Raw Poultry Manure Biochars and Amended Agricultural Soil

“…Therefore, investigating nutrients dynamic (both leaching and adsorption) by agricultural soils amended with animal-biomasses-derived-biochars is a crucial task in order to get a better appreciation of their possible impacts onto soils, water resources, and plants' growth [8]. Nutrients dynamic in biochars-amended-soils have been investigated under controlled laboratory conditions in batch, column, and pots devices and also in field trials [5,[14][15][16]. Results indicated that nutrients dynamic is a very complex process that depends on various parameters such as the physicochemical properties of the nutrient, the biochar, and the agricultural soil as well as the used experimental conditions giving the impression that outcomes of different studies look like contradictory [6,12,14,16,17].…”

“…Nutrients dynamic in biochars-amended-soils have been investigated under controlled laboratory conditions in batch, column, and pots devices and also in field trials [5,[14][15][16]. Results indicated that nutrients dynamic is a very complex process that depends on various parameters such as the physicochemical properties of the nutrient, the biochar, and the agricultural soil as well as the used experimental conditions giving the impression that outcomes of different studies look like contradictory [6,12,14,16,17]. For instance, Zolfi-Bavariani et al [6] and Hadroug et al [17] showed that more alkaline biochars, that are produced at higher pyrolysis temperatures, released higher rates of potassium.…”