Soil phosphorus distribution and concentration from repeated starter phosphorus band application

Soil sampling to determine soil phosphorus (P) availability is complicated by the presence of residual P bands that have not been disturbed by tillage . This study investigated the soil P distribution and longevity of P bands applied in no-tillage culture on a Mollic Endoaqualf soil (fine, montmorill onitic, mesic). Starter band P treatments of 0, 5, 10, and 20 kS P ha(-1) w ere applied to corn (Zen may's L.) in a no-till corn-soybean [Glycine max. CL. Merr.] rotation from 1990 through 1996. Treatments were rerandomized wi th each application, such that differing starter band histories were establ ished, which served as treatments for soil and plant sampling. In 1996 the 10 and 20 kg P ha(-1) bands were marked with monofilament line in the soil during the application process. In April 1997, contiguous 2.0 cm wide, 15 c m deep soil cores (30 per row) were taken across the 1996 corn rows. Soil c ore Bray-1 P concentrations that were 52 to 54 mg kg(-1) greater than adjac ent cores clearly indicated the presence of one and presumed three year old residual bands of 20 kg P ha(-1) treatments. Cross-sectional soil samples of these bands (1.61 cm(2) samples) had P concentrations that were 35 times that of non-blind affected soil, and band width:, were 8 to 10 cm. When sa mpled by 2.0 cm diameter cores these bands were evident in only two core sa mples. Cider evident in only two adjoining greatly decayed bands were also evident by core P concentrations that were 2 to 7 mg kg(-1) greater than ad jacent cores. Cross-section samples showed the bands had P concentrations t hat were 3 to 3 times greater than non-band affected soil. These bands 2 er e presumed to be five and seven years old. Based on the standard deviation of the 30 core sets of samples, an impractical number of samples would be r equired fur random sampling to achieve a precision level better than 4 mg P kg(-1). pooling all the soil across a row (a slice sample) reduced variabi lity enough to achieve 7 mg kg(-1) precision with 95% confidence with no mo re than 9 slices per composite sample, and P concentration; would be increa sed 3 to 2.9 mg kg(-1) relative to soil without bands. in 1997 oat (Avena s ativa L.) growing directly over 10 kg ha(-1) bands and non-band affected so il had similar whole plant P contents at Feekes growth stage 10. Yet the oa t had incrementally greater plant P contents in response to 1997 broadcast P amounts of 0, 15, 30, 44 kg ha(-1) Soil sampling strategies that variably weight band-affected soil relative to soil outside the blind only slightly influence soil P recommendations. The choice of a sampling strategy should be based on the need for accuracy and the bias desired (inclusion or exclu sion of bands). Despite the ability to measure residual soil band P to vari ous levels of precision with sampling strategies that variably weight band affected soil in the sample, soil extractable P from bands may not well rep resent P actually available to plants.