Sweet corn response to banded phosphorus in the Willamette Valley

<p>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.</p> <p>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. </p> <p>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.</p> <p>This study was funded by the Oregon Processed Vegetable Commission.</p> <p>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.</p> <p>McAndrew, D. 1983. Soil fertility investigations on soil solution composition and nutrition of sweet corn and onions. Ph. D. dissertation, Oregon State University, Corvallis.</p> <p>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. <a href="https://catalog.extension.oregonstate.edu/em9272">https://catalog.extension.oregonstate.edu/em9272</a></p>