Potassium runoff and leaching losses in beef cattle production systems of southern Chile

Livestock production in Chile is concentrated in the southern regions of the country and is largely based on a direct grazing system that has intensified over the last 10 years because of new commercial trade agreements signed by the country. This activity has increased application rates for N, P, and K fertilizer, stocking rates, and the intensity of rotational grazing. The objective of this study is to quantify K losses in surface run-off and leaching from grazed permanent pastures. Previous studies have shown that over 95% of total K loss in these Andisols is through leaching. These losses are low when no K has been added as fertilizer. No information exists on how K losses are affected by autumn application of inorganic fertilizer. There is also no information on the effect of plant uptake on K extraction in cut areas, as this pathway can be more relevant for K fertilizer rate adjustments than K leaching losses. Thus, a second objective is to quantify K leaching losses after autumn K fertilizer applications under a typical cutting regime. Three treatments (0, 60, and 120 kg K₂O/ha), applied in March 2008, and in 2009, were compared to determine the relative amounts of K lost by leaching, plant K uptake, and soil K balances.

Potassium concentration in leachate samples were lower than 6 mg K/L in 2008 and 2009, which resulted in 5 to 17 kg K/ha lost by leaching. Plant K uptake was similar for the 0, 60, and 120 kg K₂O/ha treatments, varying between an average of 521 (control) and 553 kg/ha (120 kg K₂O/ha) for the two seasons. Potassium balances were negative for all treatments (-527, -514, and -486 kg K/ha for the 0, 60, and 120 kg K₂O/ha treatments, respectively), indicating a high soil K supply. Higher K additions, through slurry, manure, or fertilizer applications, might be required in areas managed under cutting to ensure high soil K availability. Laboratory soil K adsorption studies would be needed in order to improve our knowledge in relation to soil K dynamics in Andisols. Chile-5