Exploration of Responses to Potassium in Western Uruguay

Several regions of Uruguay has recently shown K deficiencies and responses. This project looks to determine the different areas with K deficiency, evaluate responses in the main field crops, and provide information on K soil testing.

IPNI-2007-URY-2

20 Feb 2012

2011 Annual Interpretive Summary


This research is partly based on previous observations of K deficiency and responses 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, or sorghum, indicated a critical range of 0.30 to 0.40 cmol/kg (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 4 million ha have the potential for soil K deficiency in all Uruguay.

On-going field work in 2011-12 is evaluating the effects of K fertilization in winter crops (wheat and barley) and double-cropped soybean. Three of nine experiments located in the traditional agriculture area showed significant yield responses to K application in wheat or barley. Grain yield responses averaged 638, 152, and 220 kg/ha in sites with soil exchangeable levels of 0.24, 0.29, and 0.32 cmol/kg (94, 113, and 125 ppm). These experiments are being evaluated for residual effects on double-cropped soybean grain yields.

Field studies on the dynamics of K release from crop residues, have shown an increased release of K from maize and soybean stover in the early days since residue deposition. The amount of K released was associated with the type of crop and rainfall accumulation. The exchangeable K showed the highest variations in the first 3 cm deep, and was associated with the amount of K supplied by the residues.

Laboratory studies indicated that the K buffering capacity of different agricultural soils vary according to clay content, soil organic matter, and exchangeable Ca and Mg concentrations. An average rate of 184 kg/ha of applied K was needed to increase exchangeable K by 0.1 cmol/kg of exchangeable K in 36 agricultural soils, with a range of 68 to 455 kg/ha. Uruguay-02