Applying 90 lbs. of phosphate fertilizer per acre boosted soybean yields 5 1/2 bu./acre in a 2002 University of Minnesota study on a farm near Crookston, MN.
Previous research on phosphorus fertilization for soybeans in northwest Minnesota had not shown a positive yield response. However, new soybean varieties with higher yield potentials have been developed for the region over the past 10 years.
The soil at Crookston is an Ulen loamy fine sand with an Olsen phosphorus level of seven parts per million. Rates of 0, 15, 30, 45, 60, 75 and 90 lbs. of phosphate fertilizer were applied prior to planting. The soybean cultivar Legend 009 was seeded in 22-in. rows. Soybean yields increased from 37.6 bu./acre (with no added phosphorus) to 43.1 bu./acre, and protein concentration increased from 31.8 to 33.8% with the addition of 90 lbs. of phosphate.
Researchers say additional trials are needed on other varieties and soil test levels before they can recommend specific phosphorus rates for soybeans.