Concentration and Release of Phosphorus and Potassium From Lignocellulosic- and Manure-Based Biochars for Fertilizer Reuse

Abstract

Biochars pyrolyzed from plant residues and animal manure feedstocks may contain disproportionate amounts of phosphorus (P) and potassium (K). Unequal nutrient characteristics can impact the biochars ability to properly supply as well as improve soil P and K fertility levels. A soil incubation study was performed to test the hypotheses that biochar produced from poultry litter will release more water soluble dissolved P (DP) and K (DK) concentrations and would also increase soil plant available P and K concentrations as compared to lignocellulosic-based biochars. Biochar was pyrolyzed at 500 • C from hardwood waste products (HW), pine chips (PC; Pinus taeda), poultry litter (PL; Gallus domestics), and an 80:20 pine chip/poultry litter blend, which were then added at 20 g kg −1 to a sandy Norfolk E soil (Typic Kandiudult). Un-amended (no biochar) Norfolk E soil served as a control. During the incubation, all treatments were leached four times with deionized water and the leachate analyzed for DP and DK; their concentration and mass released as a function of total amounts present were then calculated. At the conclusion of the study, soils were extracted using Mehlich-1 reagent for determination of plant-available P and K contents. Leachates from soil amended with 100% PL biochar and the 80:20 blend had significantly more DP and DK mass (59 and 1,018 mg, respectively) released compared to PC and hardwood biochars (0.07 and 23 mg). Significant amounts of DP were released from PL biochar with additional water leaching, but DK release results were mixed. Soil Mehlich-1 P and K contents were significantly increased using PL biochar compared to lignocellulosic-based biochars. Blending PC with PL feedstocks at 80:20 weight ratio reduced Mehlich-1 soil P concentrations to 35 mg kg −1 , which was more aligned with soil test P levels (30-50 mg kg −1) recommended for a corn (Zea mays) production in southeastern USA Coastal Plain sandy soils. These results reveal that 100% PL biochar offers a higher potential to provide more P and K to soils than lignocellulosic based biochars, and that feedstock blends can be used to create designer biochars that align soil test fertilizer values with plant nutrient requirements.

Role of Nutrient-Enriched Biochar as a Soil Amendment during Maize Growth: Exploring Practical Alternatives to Recycle Agricultural Residuals and to Reduce Chemical Fertilizer Demand

“…Previous studies suggest however, that for biochar to make a viable contribution to soil N, P, and K nutrient pools, the nutrients need to be released into the soil solution in concentrations within ranges suitable for plant uptake and increased crop production [20]. Moreover, the rates of nutrient release in different biochar will depend on the nutrient pool in the biochar and the soil conditions [51].…”

“…Indeed, several studies have demonstrated that biochar can adsorb nitrogen (as NH 4 + -N, NO 3 − -N, and Urea), phosphorus (as orthophosphate), potassium, and organic matter from different aqueous solutions such as landfill leachates, anaerobic digestates, urine, and livestock wastewater [15][16][17][18]. As a soil amendment, biochar has been reported to offer several benefits, which include increased soil texture, soil carbon, nutrient retention, and cation exchange capacity, beside support to microbial diversity that increases mineralization and availability of nutrients in amended soils [19][20][21]. In a recent study, Fidel et al [22] evaluated the potential reduction of greenhouse gases (N 2 O and CO 2 ) emissions from biochar-amended soils based on laboratory soil incubations experiments and field scale studies under continuous cropping with four crop systems namely; no-till continuous corn, switch grass, forb mix, low-diversity and high-diversity grass mix.…”

Role of biochar in promoting circular economy in the agriculture sector. Part 1: A review of the biochar roles in soil N, P and K cycles

“…The quantification of P present in biochar is source dependent; biochars produced from nutrient-rich feedstocks, such as manure and crop residues, generally have higher P values than those from lignocellulosic feedstocks, and therefore are best suited to be used as soil P fertiliser [52,69]. For example, the study performed by Novak et al [70] showed that the concentration of total P in manure-based biochars was 53 to 105 times higher than that in lignocellulosic-based biochars and the release of dissolved P in soils amended with manurebased biochars was approximately 850 times higher than in the soils amended with lignocellulosic-based biochars.…”

“…Novak et al [70] examined the release kinetics of K and P from various biochar in fine-loamy soil in a 150-d column leaching experiment, which showed an initial rapid release of dissolved K, followed by a significant decline in the dissolved K content in the leachate from soils supplemented with either poultry litter biochar or 'designer biochar' at a blending ratio of 80:20 pine chip/poultry litter biochar. They also reported that such a blended biochar was aligned with soil P and K levels recommended for corn production in southeastern USA Coastal Plain sandy soils [70].…”

Most Plant Nutrient Elements Are Retained by Biochar in Soil

“…This is also likely to be the situation for many of the other plant nutrient elements present in biochar. The correspondence between nutrient elements in equivalent biochar and fertilizer rates rests on the assumption that elements in biochar will be released to soil solution within the growth period of crops [26]. The current research has investigated this hypothesis and the mechanisms controlling the release of nutrient elements from biochar.…”