Factors Responsible for Poor Response of Corn and Grain Sorghum to Phosphorus Fertilization: I. Soil Phosphorus Level and Climatic Factors

Field experiments designed to measure the response of corn and grain sorghum to starter fertilizer containing P in Nebraska have shown both negative and positive responses to the starter. Positive responses have been associated with low soil P levels and negative responses with high soil P. These experiments also have shown that corn and sorghum are quite efficient in utilization of soil P, making optimum yields without fertilization possible with these crops on soils of substantially lower soil P supply than is possible with small grains. Excessive vegetative growth and water use with accentuated drouth damage accounted for yield decreases due to starter P in some experiments in dry years. In other cases, it appeared that a hastened physiological development due to applied P may have left the plant in the most critical stage of the reproductive cycle when dessicating weather conditions occurred, with resulting damage that was not apparent in later or earlier corn. In still other cases, there was evidence in plant appearance of a disturbed utilization of trace element(s) where starter P was applied, which is the subject of later papers in this series.