Soil labile carbon and nitrogen fractions after eleven years of manure and mineral fertilizer applications

Manure nutrient management can affect soil carbon (C) and nitrogen (N) fractions. The objective of this study was to determine the effects of long-term manure and mineral fertilizer applications on C and N fractions. This study was conducted for 11 years under corn and soybean rotation. The study rates included low manure (LM (4,194 kg ha−1), based on the crop’s phosphorus (P) requirement), medium manure (MM (8,081 kg ha−1), based on the crop’s N requirement), high manure (HM (16,162 kg ha−1), two times the rate of MM), medium fertilizer (MF (204 kg N ha−1), recommended), high fertilizer (HF (224 kg N ha−1), high), and control. Soil samples were collected to measure C and N fractions. HM recorded higher particulate C (8%) at 0–10 cm and higher dissolved C (26%) at 10–20 cm compared to LM. All manure rates had higher permanganate oxidizable C compared to mineral fertilizer rates. Carbon management index was higher under MM compared to the HF (17%) and MF (33%). This study suggests that manure application (16,162 kg ha−1 rate and even 8,081 kg ha−1 and 4,194 kg ha−1 rates in some cases) can enhance C and N pools compared to mineral fertilizer application.