Influence of residual and fresh subsurface phosphorus fertilizer bands on soil phosphorus profile distribution and maize growth and shoot phosphorus uptake

A field study was conducted at Beresford, SD, to examine how residual fertilizer phosphorus (P) bands influenced the distribution of Bray-1 extractable P in the soil profile and maize (Zea mays L.) shoot growth and P uptake in a ridge-till system. Liquid ammonium polyphosphate (10-34-0) was injected each fall for three consecutive years in either one or two concentrated subsurface bands in a 5 x 5 cm configuration with respect to the planted seed at rates to provide either 0, 10, 20, or 40 kg P/ha. Soil samples were removed once in the spring before planting with a rectangular block sampler along a 30 cm transect perpendicular to the ridge row to a depth of 15 cm after the third year of the P application. The large sample was separated into eight 7.5 x 7.5 cm x 7.5 cm block sections. Soil was analyzed for Bray-1-extractable orthophosphate-P in each of the sample blocks, composited for increasingly greater soil volumes, and compared with shoot growth and P uptake at the sixth and twelfth leaf and silking stage of growth. Applied-P rate had a strong effect on Bray-1-P levels, increasing them from 7.5 to 195.1 mg P/kg as P rate increased from 0 to 40 kg P/ha. The locations of the previously applied P bands were highly variable in the sampling profile. Coefficients of variation (c. v.) for Bray-1-P levels varied from 1.9 to 141.4 for sampling-block locations and increased as P rate increased. This result indicated that, within treatment replication, there was little consistency with fertilizer P-band placement with respect to the planted seed, and the variability increased with higher P applications. Applied-P rate influenced shoot dry weight, shoot P concentration, and shoot P uptake in the sixth leaf and twelfth leaf growth stages only. The band number had no influence on these parameters. When increasingly larger volumes were considered to improve the accuracy of sampling position with the predictability of the Bray-1 P levels and shoot parameters, the smallest soil volume and sampling position close to the planted seed was as accurate a predictor of shoot parameter responses as the Bray-1 P levels derived from soil composites of larger sampling volumes.