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


20 Jan 2009

2008 Annual Interpretive Summary

Chilean livestock production 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 more intensive land use 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) were compared to determine the relative amounts of K lost by leaching. Potassium fertilizer was applied in autumn 2008 and losses were estimated from samples collected every 100 mm of rainfall between April and October 2008.

Preliminary results show that pasture yields increased by 8 and 12% over the control (13 t/ha/yr) with the 60 and 120 kg rates, respectively. Plant K concentration did not vary between treatments (3.8% ± 0.07%). Plant uptake was greater under the 120 kg/ha rate, in response to the greater dry matter production, varying between 450 (control) and 540 kg/ha (120 kg K/ha). Even though K leaching data are still being analyzed, the high plant K uptake results suggest that strong negative soil K balances can be expected (more than -400 kg/ha/yr) in pastures managed under cutting. It will be necessary to increase K fertilizer additions in order to maintain soil K status of these grasslands. Chile-5