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 three years of field work and other studies, including 50 experiments under wheat, barley, maize, soybean, sunflower, and sorghum crops, indicated a critical K concentration of between 0.30 to 0.40 cmol/kg (i.e., soil test K [STK] of 117 to 156 ppm), below which there is a high probability of 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 2012-13 growing season included thirteen trials - eight with full-season soybean, one with sorghum, two with wheat, and two with barley. Potassium fertilizer application increased (p=0.10) grain yield in four of the seven sites where we expected yield response because of the low STK. Grain yield responses to K fertilization averaged 2.25 t/ha (+46%) for sorghum, and ranged from 0.11 to 1.1 t/ha (+3 to 75%) for soybean compared with unfertilized controls. The variability in K response is being investigated in a long-term field experiment initiated in 2012-13 at Soriano Department where STK ranges from 125 to 211 ppm. Crops grown in low-STK areas showed a higher occurrence of visible K deficiency symptoms. Double-cropped soybean yields tended to be higher in K-fertilized treatments, but the differences were not significant.