Soil potassium dynamics in the eucalypt rhizosphere

Key Message The acceleration of K release in the eucalyptus rhizosphere is a key process for explaining plant K uptake in low-K tropical soils. Abstract We conducted a pot experiment to evaluate the short-term dynamics of soil K at the soil-root interface of eucalyptus plants. We hypothesized that eucalyptus roots are able to substantially modify the soil K supply by releasing K from more recalcitrant K pools. To test our hypothesis, we used five tropical Oxisols in which the remaining structural K forms were components of highly weathering-resistant minerals. The experiment was installed in a split-plot arrangement of treatments in a randomized block design with four replicates. The effect of the soils was studied in the main plots. In the subplots, we isolated or did not isolate eucalyptus roots from the soil. At the end of the experiment, we determined the total soil K, exchangeable K, and K extracted with Mehlich 1 (M1) and Mehlich 3 (M3) as well as the K content in plant shoots. Our main findings suggest that the acceleration of K release in the eucalyptus rhizosphere is a key process for explaining plant K uptake in low-K tropical soils. Understanding and quantifying the processes related to this phenomenon are necessary to provide a more mechanistic basis for K fertilization recommendations as well as to monitor the sustainability of natural and planted eucalypt forests