Exploration of Responses to Potassium in Western Uruguay

This research is based on previous observations of K deficiency and responses to K fertilization in field crops grown within the northwestern Uruguay region. Data from the first 3 years of field work and other studies, including 50 experiments under wheat, barley, maize, soybean, sunflower, and sorghum, indicated a critical K concentration of 0.30 to 0.40 cmol/kg (i.e., soil test K [STK] of 117 to 156 ppm). Below this K concentration, there is a high probability of a positive yield response to K fertilization. Integration of soil survey data with this field work has allowed researchers to estimate that an area of 4 million ha is potentially K deficient in Uruguay.

Field work in the 2013-14 growing season included field experiments evaluating K response, residual effects of K application to previous crops, and two experiments evaluating the time of application. Potassium fertilizer application increased grain yield at one site where we expected yield response because of the low STK, but no responses were observed at two sites under high soil K availability. A residual study evaluating effects of fertilization for a 2012/13 soybean crop on a subsequent 2013/14 wheat crop, showed significant responses, which indicates an ability to fertilize for two successive crops at once, an interesting alternative providing flexibility for farmers and agricultural services. At two soybean studies, K application 70 days after planting was not different from K applied at planting.

A brochure on “Right Potassium Management of Field Crops of Uruguay”, produced by Facultad de Agronomia (UdelaR) with Canpotex and IPNI support, has been released and made available for fertilizer dealers, farmers and agronomists. The brochure is available at the IPNI website at http://lacs.ipni.net/article/LACS-1217.