Soybean yield and Seed N concentration in response to in‐season poultry litter application

Abstract

North Carolina is a major poultry‐producing region, generating quantities of poultry litter (PL), a cost‐effective organic fertilizer. Because PL nutrient release must be synchronized with crop demand, application timing is important, and PL is applied before planting. Timely application can be limited by the busy planting season, wet spring conditions, and litter hauling. Although interest in in‐season nitrogen (N) application is increasing, research on in‐season PL application remains limited due to concerns about crop damage. Therefore, this study evaluated the effects of PL rate and timing on soybean ( Glycine max (L.) Merr.) yield and seed N concentration. Field experiments were conducted at 3 site‐years in North Carolina in 2023 and 2024 using PL rates of 0, 73, 146, 292, and 585 kg plant‐available N ha ⁻¹ at planting, V2, and R1. Soybean response varied by site‐year. At 1 site‐year with low initial soil fertility and unfavorable early growing conditions, PL at 73 kg N ha ⁻¹ increased yield by 71% relative to the control, whereas higher rates provided no benefit. Within each site‐year, yield did not differ among application timings. Seed N concentration varied only by site‐year. Compared with PL at a similar rate applied at R1, urea ammonium nitrate (UAN) increased leaf N concentration at the reproductive stage by 13%, but yield and seed N concentration did not differ between PL and UAN. These results indicate that PL can be an effective alternative to UAN under low fertility conditions and that application timing from planting to R1 had little influence on soybean yield when applied at agronomically appropriate rates.