Nutrient Management Research Database

Integrating information on nitrogen (N) mineralization potentials into a fertilization plan could lead to improved N use efficiency. A controlled incubation mineralization study examined microbial biomass dynamics and N mineralization rates for two soils receiving 56 and 168 kg N ha⁻¹ in a Panoche clay loam (Typic Haplocambid) and a Wasco sandy loam (Typic Torriorthent), incubated with and without cotton (Gossypium hirsutum L.)residues at 10 and 25°C for 203 days. Microbial biomass activity determined from mineralized carbon dioxide (CO₂) was higher in the sandy loam than in clay loam independent of incubation temperature, cotton residue addition and N treatment. In the absence of added cotton residue, N mineralization rates were higher in the sandy loam. Residue additions increased N immobilization in both soils, but were greater in clay loam. Microbial biomass and mineralization were significantly affected by soil type, residue addition and temperature but not by N level.

• This lab incubation investigated changes in mineralization rates and soil microbial behavior stimulated by fertilization, cotton residue incorporation, and temperature.
• Mineralization of background soil N can inform nutrient management planning, helping to limit costs of N fertilization.
• However, predicting mineralization rates has proven difficult, limiting the ability of growers to reliably utilize this potential source of N.
• Application of plant biomass with high C:N ratios can result in immobilization, a process where microbes take up soil N and limit its availability to plants.
• Two soil types were included in the study: a clay loam and a sandy loam.

• Total microbial activity was higher in the sandy loam than in the clay loam across both soil types and for all amendment treatments.
• The application of cotton residue increased N immobilization rates. This effect was more pronounced in the clay loam.
• Without cotton residue addition, mineralization rates were higher in the sandy loam.
• Rates of N fertilization studied (50 lbs N/ac and 150 lbs N/ac) did not alter N mineralization rates.
• This study highlights the importance of considering texture when incorporating potential N mineralization