Soybean Yield and Plant Response to Phosphorus Fertilization

Abstract

Phosphorus (P) is a key limiting nutrient for soybean production in South Dakota. Soil tests have been used as a baseline indicator for plant available P and fertilizer recommendations for over a century. Plant nutrient analysis may be used to complement a soil test as a way to validate fertilizer and management practices. Soybean nutrient sufficiency ranges have only been slightly adjusted since they were published in the 1960’s. The objectives of this study were to update the soil test P and soybean plant P sufficiency level in South Dakota and to recognize implications of improper plant sampling. We also wanted to differentiate between nutrient concentration and nutrient uptake. A randomized complete block design was used for this experiment in Eastern South Dakota at eleven locations in 2013, and ten locations in 2014. Triple Super Phosphate (TSP)-fertilizer treatments were broadcast applied at the following rates: 0, 22, 45, 67, 90 kg P2O5 ha-1. Data collected included pre-plant soil samples, plant tissue samples at V4, R2 and R6.5 growth stages. In addition, grain samples and yield was measured. Tissue samples were analyzed for total P and soil samples were analyzed for Olsen, Bray-P1 and Mehlich 3 P. There were no significant differences in yield across locations in either year of the study. Grain P concentration increased at higher P rates. Failing to remove the petiole diluted trifoliolate P concentration by 15 to 18% . Improper plant sampling methods result in inaccurate nutrient data to make management decisions with. Fertilizer recommendations should be reevaluated with economic optimum in mind