Nutrient Cycling in Bioenergy Crop Systems for Fuel Production by Pyrolysis.

Pyrolysis is a low oxygen thermoconversion of biomass that produces char, bio-oil and gas products. All these products can be used as fuels. Pyrolysis char also has potential as a soil amendment. Char adds a recalcitrant carbon source with capacity to increase nutrient retention, support the soil microbial community, and increase the water holding capacity in some soils. Depending on the feedstock, pyrolysis chars contain nutrients that may be plant available. For example, peanut hull char contains 14.4 g N kg ^-1, 0.7 g P kg ^-1, 6.3 g K kg ^-1, and poultry litter char is higher at 34.7 g N kg ^-1, 30.1 g P kg ^-1, and 51.1 g K kg ^-1. These high nutrient chars may help close the nutrient cycle for energy crops by supplying and retaining nutrients in the cropping system. Data on low temperature pyrolysis chars from common feedstocks in the southeastern United States indicate that N, P, and K are concentrated in the char by pyrolysis. Although N in the pyrolysis char does not appear to be readily available for crops, nutrients such as K, Ca, and Mg do appear to be plant available. Sorption studies indicate that NH₄-N and P are retained by some pyrolysis chars. Removal of crop residues for bio-energy production can lead to depletion of soil organic carbon (SOC) with deleterious effects on soil fertility. Pyrolysis of biomass and returning char to the soil may offer an opportunity to generate energy while sequestering C and improving soil nutrient status.