Nitrogen and Carbon Mineralization from Organic Amendments and Fertilizers Using Incubations with Sandy Soils

Synthetic fertilizers are the main nitrogen (N) input used in specialty crop systems established on sandy soils of Florida, although organic amendments and fertilizers can be used as a substitute. Organic N contained in these products must be mineralized before crop uptake, which is affected by amendment properties, soil properties, and temperature. A better method for predicting N release can help maximize the nutrient cycling benefits of organic amendments and fertilizers while avoiding negative environmental impacts. The main objective of this study was to measure N release and CO2 emissions from two poultry manure-based amendments (PMA) and two processed organic fertilizers (OF) made from livestock byproducts (e.g., feather meal). We conducted an 8-week incubation using two sandy Florida soils belonging to two soil orders (Entisol and Spodosol) and with a greater than two-fold difference in soil organic C. We incubated these soils at 10 °C, 17 °C, 24 °C, and 30 °C, measured plant-available N at 0, 1, 4, and 8 weeks, and measured CO2 emissions weekly. In both soils, OF released more inorganic N and at a faster rate compared with PMA, but CO2 emissions were greater from PMA than OF. Nitrogen mineralization and CO2 emissions increased with temperature, but temperature effects were less important than expected. These results on the mineralization of PMA and OF in sandy soils are key to optimize their use and management in Florida and other areas dominated by sandy soils.