Fertilizer use is a key management practice for growers who seek to maximize profit from their soybean acres. Previous research on soybean phosphorus fertility in NW Minnesota had not shown a positive yield response with band or broadcast applications. New soybean cultivars with higher yield potentials have been developed for the region over the past ten years prompted the idea to conduct a phosphorus rate study to determine if the phosphorus nutritional needs of the crop were still being met from residual phosphorus in the soil.

The soybean phosphorus rate study was established at the Ron Peterson farm northeast of Crookston, MN. on a Ulen loamy fine sand soil type with an Olsen phosphorus level of 7ppm. Phosphorus treatments of 0, 15, 30, 45, 60, 75 and 90 pounds of P2O5/acre were applied prior to planting using a randomized complete block design with four replications. The soybean cultivar Legend 009 was seeded in 22 inch rows and maintained during the growing season using normal cultural practices by the grower and harvest was performed with a plot combine. Yield, protein content and oil percentage were measured and all adjusted to 13 percent moisture basis.

There was a highly significant linear yield (P=.001) and protein concentration (P=.0002) response to phosphorus rates as can be seen in Figures 1 & 2. Soybean yields increased from 37.6 bushels per acre with no added phosphorus to 43.1 bushels per acre with the addition of 90 pounds of P2O5.. Protein concentration increased from 31.8% with no added phosphorus to 33.8% with the addition of 90 pounds of P2O5 per acre (Table 1).

Additional trials are needed on other cultivars and soil test levels to confirm the need for phosphorus nutrition for increased soybean yield and protein concentrations.

I would like to extend a special thanks to Ron Peterson for providing the research site, the Minnesota Soybean Research and Promotional Council for partial financial support and the Northwest Research and Outreach Center at Crookston for assistance with the study.