Phosphorus Status of Horizons of Four Benchmark Loessial Soils of the Central Great Plains Region

Abstract Genetic horizons of the Colby, Weld, Rago, and Keith loessial soil series were investigated. Buried soils occurred in the Rago and Keith series. Each horizon was subjected to various chemical analyses and used in greenhouse fertilizer studies. Marked differences in P content and availability to plants occurred among horizons and with profile depth. Yields and plant uptake of N and P from nonphosphated horizons were positively correlated with the initial NaHCO 3 ‐soluble P in the soils when N was uniformly applied. By adding 8.8 or 35.2 ppm P per pot, yields were similar within a given horizon, but differed markedly among horizons of the same profile. With adequate N added, spring barley ( Hordeum vulgare L. ‘Moravian’) yields from the Rago A‐B subsoil horizon and the Rago Ap surface soil were similar, but the Weld B3ca subsoil horizon yielded 50% more than the Weld Al surface soil. All other subsoil horizons were deficient in available P, and maximum yields occurred only when both N and P were added. Fertilized subsoils producing more dry matter yield than their respective surface soils were: Colby AC, Cca, and C; Weld B3ca, Cca, and C; and the Rago B21, A1b, B2bca, B3bca, and C. Fertilized subsoils producing yields similar to their surface soils were: Weld B22; Rago A‐B; and the Keith A1b, B2b, B3bca, Cbca, and C. The remaining fertilized subsoils (Weld B21 and Keith B2 and B2ca) produced less yield than their respective surface soils.