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Nitrogen cycling in pasture soils differing in drainage characteristics and fertilization legacy needs more research to determine efficient nutrient management strategies. This study compared differences in nitrate (NO3−), ammonium (NH4+), inorganic N (IN = NO3− + NH4+), potentially mineralizable nitrogen (PMN), loss-on-ignition carbon (C), and soil pH in 10, 0.7 ha pastures in Eatonton, Georgia, historically fertilized with the same amount of N as either broiler litter (BL; >15 years, 6 pastures) or mineral fertilizer (Min; 4 pastures). We sampled to 90 cm (0–5, 5–10, 10–20, 20–40, 40–60, and 60–90 cm) on a 20 m grid. An analysis of variance indicated that below 5 cm BL pastures had significantly greater amounts of NO3−, IN, PMN, and soil pH compared to Min pastures. Comparisons of drainage classes (well drained~WD, moderately well drained~MWD, and somewhat-poorly drained~SPD) for each BL and Min were analyzed using linear regression for C:IN, C:PMN, pH: NO3−, and pH: NH4+ with all depths combined. In MWD soils, BL had 0.1 and 0.2 mg N kg−1 greater PMN and IN, respectively, for each unit increase in C. In WD soils NO3− decreased in BL by 7.4 and in Min by 12.1 mg N kg−1, while in MWD soils, this level decreased in BL by 7.8 and in Min by 4.5 mg N kg−1 for each pH unit. Five years after N fertilization stopped, BL soils have retained more inorganic N but are losing more NO3− at a greater rate in the MWD soils when all depths are considered. These losses are a combination of plant uptake, emissions, runoff and leaching. While more research is needed, these results strongly suggest the need to design N fertilization practices with drainage class and fertilization legacy in mind to improve N-use efficiency. |
