Nancy Thiex

Determination of Nitrogen, Phosphorus, and Potassium Release Rates of Slow- and Controlled-Release Fertilizers: Single-Laboratory Validation, First Action 2015.15.

A previously validated method for the determination of nitrogen release patterns of slow- and controlled-release fertilizers (SRFs and CRFs, respectively) was submitted to the Expert Review Panel (ERP) for Fertilizers for consideration of First Action Official Method(SM) status. The ERP evaluated the single-laboratory validation results and recommended the method for First Action Official Method status and provided recommendations for achieving Final Action. The 180 day soil incubation-column leaching technique was demonstrated to be a robust and reliable method for characterizing N release patterns from SRFs and CRFs. The method was reproducible, and the results were only slightly affected by variations in environmental factors such as microbial activity, soil moisture, temperature, and texture. The release of P and K were also studied, but at fewer replications than for N. Optimization experiments on the accelerated 74 h extraction method indicated that temperature was the only factor found to substantially influence nutrient-release rates from the materials studied, and an optimized extraction profile was established as follows: 2 h at 25°C, 2 h at 50°C, 20 h at 55°C, and 50 h at 60°C.

Compositional Analysis of Microwave Chemically Treated Biomass Samples

The compositional analysis of slurries generated from the microwave-assisted pretreatment of switchgrass, prairie cordgrass, and distillers dried grains with solubles were investigated. The biomass samples were treated under acidic, alkali or neutral conditions at 1200 W and 200°C for 10 min. The supernatants were analyzed for sugars, whereas the compositional analysis of the remaining solid fractions was performed using an integrated scheme based on the Standard Laboratory Analytical Procedures for raw biomass developed at the National Renewable Energy Laboratory. The experimental results show that little to no arabinose was found in these treated substrates. Substrates treated under alkaline conditions resulted in the highest carbohydrate content with the lowest lignin amount, whereas acidic pretreatments with 0.5 % H2SO4 resulted in hemicellulose-free biomass. A minute amount of hemicellulose was still present in prairie cordgrass and switchgrass after treatment with 0.2 % H2SO4 and this amount increased for pretreatments with H2O and 0.3 % H2O2. Pretreatments under alkaline conditions with 1 % NaOH were the least aggressive treatments methods because they retained the most carbohydrates in the biomass pulp while having the lowest lignin amount.