Sweet corn response to banded phosphorus in the Willamette Valley

Introduction The previous Oregon State nutrient management guide for sweet corn (Hart et al., 2010) recommended application of banded P fertilizer at planting for fields testing less than 50 mg kg-1 P, using the Bray method. Soil test P is above the 50 mg kg-1 response threshold in most vegetable production fields in the Willamette Valley. At 15 field sites we sampled in 2012-2013, soil test P (0- to 30 cm depth) ranged from 41 to 189 mg kg-1 (median = 127 mg kg-1). In spite of high soil test P values, many growers routinely apply P in starter fertilizer formulations to sweet corn. The most common starter fertilizer formulations used to supply N (granulated monoammonium phosphate [11-52-0] and liquid ammonium polyphosphate [10-34-0]) also supply P. For example, when 10-34-0 is used to supply N at 34 kg N ha-1, P is applied at 50 kg P ha-1. Sweet corn varieties grown today are different than those grown when P fertilizer trials with sweet corn were last conducted by Oregon State in the Willamette Valley (McAndrew, 1983). Most current processing corn varieties are higher-yielding and have greater resistance to root rot diseases compared to ‘Golden Jubilee,’ the variety that dominated production prior to 1998. The objectives of this study were: 1. Evaluate corn ear yield and quality response to starter P fertilizer, using contemporary corn varieties and production practices; 2. Determine whether OSU Extension recommendations for starter P application (Hart et al., 2010) are supported by recent data.

Materials and Methods In six field experiments, corn was seeded at a target rate of 70,000 seeds/ha with starter P rates of 0, 7, 15, 29, or 59 kg P ha-1. Four trials were conducted in 2012, and two trials were conducted in 2013. Treatment plots were arranged in a randomized complete block design with four replications. In grower fields, each treatment plot was 7.6-9 m wide by 20-23 m long, and plots were positioned within the field so that irrigation was uniform across the plot area. Soil textures at field locations were silt loam or silty clay loam. All P fertilizer treatments received the same rate of N (28 kg N ha-1 in starter fertilizer plus additional N fertilization per grower practice). Starter fertilizer mixtures were prepared for each treatment using dry granular fertilizers (MAP [11-52-0], urea [46-0-0]), and K Mag [0-0-21-11Mg-21S]. For the zero P treatment, all of the starter N was urea. At the highest rate of P (49 kg ha-1), all of the N was supplied by MAP. A uniform rate of KMag was included in the starter fertilizer for all treatments, supplying 47 kg K ha-1, 28 kg Mg ha-1, and 53 kg S ha-1. The starter fertilizer band was placed 5 cm below and 5 cm beside the seed row, using a hand-push fertilizer spreader.

Results Corn ear yield did not increase when P fertilizer was applied; ear yields with and without starter P fertilizer were not statistically different at P =0.05 at any of the six field locations. At a single field site with the lowest soil test P (Corvallis 1, 42 mg kg-1 Bray soil test P, seeded May 14, 2013), corn grown without P fertilizer showed visual symptoms of P deficiency at the V6 to V7 growth stage. The P-deficient plants were shorter and had lower biomass, although whole-plant P concentration (3.0 g kg-1 P) was similar to that of P-fertilized plants. At harvest, ear yields at this site were the same for all P fertilizer treatments, including the zero P control. Results of these trials support a 50 mg kg-1 P sufficiency threshold for soil test P (Bray method; 0-30 cm depth) for modern sweet corn hybrids. See Sullivan et al. (2020) for additional P management recommendations for sweet corn.

This study was funded by the Oregon Processed Vegetable Commission.

References Hart, J., Sullivan, D., Myers, J., & Peachey, R. 2010. Nutrient management guide for sweet corn: Western Oregon. EM 9010, Corvallis, OR: Oregon State University Extension Service.

McAndrew, D. 1983. Soil fertility investigations on soil solution composition and nutrition of sweet corn and onions. Ph. D. dissertation, Oregon State University, Corvallis.

Sullivan, D.M., Peachey E., Heinrich A. & Brewer L.J. 2020. Nutrient and Soil Health Management for Sweet Corn (Western Oregon). EM 9272. Oregon State University Extension. https://catalog.extension.oregonstate.edu/em9272