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


22 Jan 2010

2009 Annual Interpretive Summary

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 permanent pastures grazed with different stocking rates. 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.

Pasture yields were increased by 10% with increasing K addition, in relation to the control treatment (11.8 t DM/ha/yr), but K plant concentration did not vary between treatments (average 3.6 ± 0.15%). Plant uptake was greater in the 120 kg K2O/ha treatment, in response to the greater DM yield, varying between 495 (control) and 602 kg/ha (120 kg K2O/ha). Potassium concentration in leachate samples varied between 2 and 3 mg K/L in 2008, with no differences between treatments, which resulted in 13 to 17 kg K/ha lost by leaching. Results of 2009 leachate samples are being processed.

High plant uptake during both seasons resulted in negative soil balances (-450 to -516 kg K/ha). This suggests that higher K additions are required in areas managed under cutting with no slurry or manure application. Also, field experiments should be complemented with laboratory soil K adsorption studies in order to improve our knowledge in relation to soil K dynamic in Andisols. Chile-5