Interest in the use of biochar in agriculture has increased exponentially during the past decade. Biochar, when applied to soils is reported to enhance soil carbon sequestration and provide other soil productivity benefits such as reduction of bulk density, enhancement of water-holding capacity and nutrient retention, stabilization of soil organic matter, improvement of microbial activities, and heavy-metal sequestration. Furthermore, biochar application could enhance phosphorus availability in highly weathered tropical soils. Converting the locally available feedstocks and farm wastes to biochar could be important under smallholder farming systems as well, and biochar use may have applications in tree nursery production and specialty-crop management. Thus, biochar can contribute substantially to sustainable agriculture. While these benefits and opportunities look attractive, several problems, and bottlenecks remain to be addressed before widespread production and use of biochar becomes popular. The current state of knowledge is based largely on limited small-scale studies under laboratory and greenhouse conditions. Properties of biochar vary with both the feedstock from which it is produced and the method of production. The availability of feedstock as well as the economic merits, energy needs, and environmental risks—if any—of its large-scale production and use remain to be investigated. Nevertheless, available indications suggest that biochar could play a significant role in facing the challenges posed by climate change and threats to agroecosystem sustainability.

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.

Off‐site transport of excess soil P from repeated P fertilizer applications constitutes waste of a vital resource and poses an environmental risk. Excess P can be mined by growing crops without P addition until it is exhausted to the point of P deficiency. This study evaluated the utility of the “soil phosphorus storage capacity” (SPSC) as an indicator of safe P mining for acid soils. The SPSC predicts crop‐available legacy P in absolute terms, (i.e., kg ha−1; can be calculated from mg kg−1 if the bulk density and soil depth are known), which is not provided by current soil tests. Results show that mining provides sufficient P for crops when there is adequately negative SPSC. This study provides a “proof‐of‐concept” for SPSC, serving as an indicator of legacy P mining prior to the need for P fertilizer application. However, further study is needed to determine the negative P thresholds more precisely at which P mining would no longer provide adequate P for optimum crop yields.

The influence of the magnetic field on some kinetic crystallization parameters of the systems zinc sulfate -water and copper sulfate -water were investigated in a series of controlled batch cooling experiments. The solutions were exposed to magnetic fields with different intensities, up to a maximum of 0.7T. A clear influence of magnetic field on the zinc sulfate crystallization parameters was found: an increase in the saturation temperature, a decrease in the metastable zone width, and increased growth rate and average crystal size. These effects were observed for the diamagnetic zinc sulfate, but not in similar experiments with paramagnetic copper sulfate.

The effect of magnetic field on the crystallization of diamagnetic zinc sulfate was investigated in a series of controlled batch cooling experiments. Zinc sulfate solutions were exposed to magnetic fields of different intensities, up to a maximum of 0.7T. A clear influence of magnetic field on the following zinc sulfate crystallization parameters was found: an increase in saturation temperature, a decrease in metastable zone width, and an increase in growth rate and average crystal size. These effects were observed for the diamagnetic zinc sulfate, but not in similar, previously reported experiments for paramagnetic copper sulfate