Northeast Research and Demonstration Farm
A long-term study was established in 1979 to evaluate the effect of various combinations of phosphorus (P) and potassium (K) fertilizer rates on soil-test values and grain yields of corn and soybeans grown in rotation. Both crops are grown each year by alternating crops between two halves of the experimental area. The predominant soil is Kenyon loam, and soil pH is 6.7. Most treatments are applied annually and consist of combinations of 0, 46, or 92 lb P2 O5 /acre and 0, 72, or 144 lb K2 O/acre. Two additional treatments (92 lb P2 O5 /acre and 144 lb K2 O/acre) are applied every other year to corn or soybeans. Granulated fertilizers (triple superphosphate and potassium chloride) are broadcast in the fall. Corn residues are chisel plowed in the fall, and both corn and soybean residues are disked or field cultivated in spring. Anhydrous ammonia is applied in spring only for corn at rates of 150 to 180 lb N/acre.
Iowa State University
Mallarino, Antonio P. and Pecinovsky, Kenneth T., "Long-term Phosphorus and Potassium Fertilization Strategies for Corn-Soybean Rotations" (2004). Iowa State Research Farm Progress Reports. 1382.