Do Your Soybeans Have the Right Stuff?.

Phosphorus is a key limiting nutrient for soybean production in South Dakota.  Soil tests have been used as a baseline indicator for fertilizer recommendations for over a century.  Plant tissue analysis may be used to complement a soil test as a way to validate fertilizer and management practices.  Soybean plant nutrition sufficiency ranges were first published in the 1960’s, and need to be reevaluated.  The objectives of this experiment were to update the soil test P and soybean plant tissue P categories in South Dakota and to recognize the implications of improper plant tissue sampling.  A RCBD was used for this experiment at five locations in eastern SD in 2013.  Phosphorous fertilizer (0-46-0) treatments were broadcast at the following rates: 0, 20, 40, 60, 80 lbs P₂O₅/acre.  Data collected included pre-plant soil samples, plant tissue samples at V3-V4 and R1-R2, grain samples and yield components.  Initial results of this experiment show no significant increase in yield was achieved with P fertilization on soils currently testing in the medium to high category. However, trifoliolate and petiole P concentrations increased with increasing P rates up to 40 lbs/ac. Improper plant sampling methods by including the petiole did result in inaccurate sufficiency interpretations.