Potassium bioavailability in a tropical kaolinitic soil

Authors: VOLF, MARCELO - Sao Paulo State University (UNESP); CRUSCIOL, CARLOS A - Sao Paulo State University (UNESP); DE AZEVEDO, ANTONIO - Sao Paulo State University (UNESP); THOMPSON, MICHAEL - Iowa State University; Kovar, John; ROSOLEM, CIRO - Sao Paulo State University (UNESP)

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2021
Publication Date: 10/7/2021
Citation: Volf, M.R., Crusciol, C.A.C., De Azevedo, A.C., Thompson, M.L., Kovar, J.L., Rosolem, C.A. 2021. Potassium bioavailability in a tropical kaolinitic soil. Agronomy. 11(10). https://doi.org/10.3390/agronomy11102016.
DOI: https://doi.org/10.3390/agronomy11102016

Interpretive Summary: Some plant species are efficient in recycling potassium (K) in agricultural systems, and can utilize less bioavailable chemical forms of soil K. The aim of this study was to assess K use by soybean (Glycine max L., Merr.), maize (Zea mays L.), and ruzigrass (Urochloa ruziziensis) grown in a highly weathered tropical soil high in nonexchangeable K, which is not readily available to plants. With a greenhouse experiment conducted with the three crops, fertilized or not with K, we found that nonexchangeable K contributed up to 80% of the K supply, depending on the plant species. In the first of three growing seasons, soybean and maize took up more nonexchangeable K than ruzigrass. In contrast, during the second and third growing seasons, ruzigrass was more efficient in acquiring nonexchangeable K. As hypothesized, soil nonexchangeable K content decreased over time when K fertilizer was not applied. The results suggest that ruzigrass can acquire relatively more of the strongly bound nonexchangeable soil K than maize and soybean. Therefore, the introduction of this species in production systems may improve the use efficiency of soil and fertilizer K. The results of this work improves our understanding of K cycling in diverse soils, and will contribute useful information to corn and soybean producers in both Brazil and the United States.

Technical Abstract: Some plant species are efficient in utilizing nonexchangeable forms of potassium (K), which bind to specific mineral sites with greater energy than does exchangeable K. The aim of this study was to assess nonexchangeable K use by three selected crop species grown in a tropical Ultisol with low exchangeable K. A greenhouse experiment was conducted with soybean (Glycine max L., Merr.), maize (Zea mays L.), and ruzigrass (Urochloa ruziziensis) grown in a tropical soil with or without K fertilization for three growing cycles. The cropped soil was compared with a control soil without plants. Nonexchangeable K contributed more than 80% of the K demand of the plants. In the first growing cycle, soybean and maize took up more nonexchangeable K than ruzigrass. However, in the second and third cycles, ruzigrass took up more nonexchangeable K than the other plant species. The contribution of nonexchangeable K to plant nutrition decreased from the first through third cycles. Nonexchangeable K was utilized after exchangeable K was depleted. Subsequently, as plants began to depend on nonexchangeable K, nonexchangeable K uptake and yields decreased. Ruzigrass was very efficient in acquiring nonexchangeable K. Therefore, the introduction of this species in production systems may improve the use efficiency of soil and fertilizer K.