Evaluating Starter P Fertilizer Response By Newer Sweet Corn Hybrids.

Research to verify university recommendations for starter P fertilizer application for sweet corn has not been conducted since the 1980s in western Oregon.  Since then, typical soil test P values have increased substantially, and newer corn hybrids have been selected for resistance to root rot diseases.   Higher soil test P and more prolific root systems should decrease P fertilizer requirements.  The present study was initiated to learn whether growers can reduce or perhaps eliminate starter P fertilizer application while maintaining ear yield and quality. Three trials were conducted on the university research farm, and three larger scale trials were conducted in grower fields.  Starter P fertilizer was applied 5 cm below and 5 cm  to the side of the seed row at 0, 17, 34, 67, and 134 kg P₂O₅/ha.  All treatments received equal banded N at planting, achieved by application of blended mono-ammonium phosphate (11-48-0) plus urea.  Soil temperatures at 10 cm depth ranged from 15 to 21 ^oC during the first two weeks after seeding.  Preplant soil test P (0 to 30 cm) at trial locations ranged from 40 to 130 mg/kg via Bray P1 method.  Plant Root Similator Probes (Western Ag Innovations, Saskatoon, SK) placed in zero P field plots at 10 cm depth adsorbed < 2 to 10+ µg P/10cm² in 14-d burials.  Ear yields ranged from 22 to 34 Mg/ha across the 6 field locations.   Ear yield did not respond to P fertilizer application at any of the 6 fields. At the field with the lowest soil test P (40 mg/kg), starter P increased biomass and P uptake (V6 growth stage), and it increased ear quality at harvest.  Results support recommendation in OSU Nutrient Management Guide for Sweet Corn (EM 9010): zero or minimal P fertilizer application when Bray P1 test exceeds 50 mg/kg (0-12 inch depth).