The capability to determine nitrogen availability of composts is necessary to ensure that such materials will provide sufficient fertilization to the growing crop and cause minimal environmental degradation. A greenhouse study using tall fescue as a bioindicator was used to evaluate nitrogen availability of two biosolids composts, two mixed yard waste-poultry manure composts, and one commercially-processed poultry litter. Five inorganic nitrogen (as NH4NO3-N) treatments applied at 0, 22.5, 45, 67.7, and 90 mg N/kg soil were employed to establish an N calibration curve. Yield, fescue biomass total nitrogen (as total Kjeldahl N (TKN)), and soil TKN and KCl extractable NO3−-N and NH4+-N concentrations of the organically amended treatments were compared to the inorganically fertilized treatments to determine amendment N mineralization rates and N fertilizer equivalent values (NFEV). Nitrogen mineralization rates were greatest in the poultry litter (21%) and Panorama yard waste compost (5%) amended pots. The NFEV of these amendments were 49% and 10%, respectively. Wolf Creek biosolids compost and Huck's Hen Blend yard waste compost immobilized N (−5% and 0.18%, respectively), and had percent NFEV of −0.66% and 0.19%, respectively. Rivanna biosolids compost immobilized N (−15%), but the NFEV was 30% due to the relatively high inorganic N content in the amendment. Nitrogen mineralization and NFEV were generally greater in amendments with greater total N concentrations and lower C:N values. The total N concentration and C:N values were less reliable variables in predicting N mineralization and percent NFEV when a significant portion of the total N was in the inorganic form. Nitrogen equivalency value and N mineralization for each amendment increased with time of sampling, indicating the potential for early season N insufficiency to plants fertilized with compost due to lack of synchrony between N mineralization and plant N needs.
All Science Journal Classification (ASJC) codes
- Waste Management and Disposal
- Soil Science