Potentially Mineralizable Nitrogen in Grazed Pastures with Well-Drained and Drainage-Impeded Soils Under Broiler Litter and Mineral Fertilization Legacies

As drainage-impeded soils cover extensive acreage that is widely used as grazed pastures, understanding how they retain organic matter and potentially mineralizable N may be important for improving management. We evaluated the vertical distribution of potentially mineralizable N (PMN), carbon, and phosphorus (M1P) in pastures with well-drained (WD) and drainage-impeded (Dimp) soil under broiler litter (BL) and mineral (Min) fertilization legacies. The study was conducted on ten 0.8 ha pastures in Eatonton, Georgia. In BL pastures, WD soils had greater PMN (40–90 cm) and LOI (0–90 cm) but lower M1P (20–90 cm) compared to Dimp. In Min pastures, WD soils had greater PMN (0–40 cm) and LOI (0–90 cm) but lower M1P (5–10 and 40–90 cm) compared to Dimp. These results suggest carbon loss in Dimp soils, probably occurring due to wetting and drying cycles. The results also suggest more P downward movement in Dimp than in WD soils. Stepwise regression identified the most significant variables related to PMN; M1P accounted for most of the variability in Min WD, LOI accounted for the most variability in Min Dimp, and BL WD, and pH accounted for most variability in BL Dimp across all depths. Our findings indicate that drainage-impeded (moderately well-drained and somewhat poorly drained) pasture soils retain C and mineralize N differently than well-drained soils.