Unraveling the role of ruzigrass in soil K cycling in tropical cropping systems

Authors: VOLF, MARCELO - Sao Paulo State University (UNESP); CRUSCIOL, CARLOS - Sao Paulo State University (UNESP); Kovar, John; ROSOLEM, CIRO - Sao Paulo State University (UNESP)

Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2023
Publication Date: 4/14/2023
Citation: Volf, M.R., Crusciol, C.A., Kovar, J.L., Rosolem, C.A. 2023. Unraveling the role of ruzigrass in soil K cycling in tropical cropping systems. Nutrient Cycling in Agroecosystems. 126:181-194. https://doi.org/10.1007/s10705-023-10283-z.
DOI: https://doi.org/10.1007/s10705-023-10283-z

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 how soybean (Glycine max L., Merr.) cropping systems differ in utilizing nonexchangeable K, which is not readily available to plants. With a three-year field experiment conducted in central Brazil, soybean was grown with and without K fertilizer in a monocropping system with fallow in the off-season, in rotation with ruzigrass (Urochloa ruziziensis) in the off-season, and following a ruzigrass pasture grown for 30 months. The plots with ruzigrass were grazed from May to September each year. Short- and long-season maturity groups of soybean were included. Soybean grain yields were not decreased in the absence of K fertilizer when soybean was cropped after ruzigrass pasture or in rotation with ruzigrass. Potassium cycling was improved when ruzigrass was included in the cropping system because ruzigrass acquired soil nonexchangeable K, which was then released in plant-available form. As expected, the long-season cultivar took up more nonexchangeable K than the short-season cultivar. No response to K was observed for soybean cropped in rotation with ruzigrass, suggesting that this management practice can eventually lead to soil K depletion in the absence of fertilizer application. 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: Solution and exchangeable K (Ke) are not the only forms of soil K available to plants; non-exchangeable (Kne) forms can also be taken up. Cropping systems that include plant species able to acquire this K fraction can impact K use efficiency. This study aimed to assess how cropping systems differ in utilizing Kne. Three cropping systems in Central West Brazil were studied for three years in the presence and absence of K fertilization: i) soybean (Glycine max L. Merr.) in a monocropping system with fallow in the off-season; ii) soybean in rotation with ruzigrass (Urochloa ruziziensis) in the off-season; and iii) soybean following a ruzigrass pasture grown for 30 months. The plots with ruzigrass were grazed from May to September each year. Two maturity groups (8.2, early, and 8.6, late) of soybean were used. Soybean grain yields were not decreased in the absence of K fertilizer when soybean was cropped after ruzigrass pasture or in rotation with ruzigrass. Potassium cycling was improved when ruzigrass was included in the cropping system because ruzigrass acquired soil Kne, which was then released in available form. The late cultivar took up more Kne than the early cultivar. No response to K was observed for soybean cropped in rotation with ruzigrass, indicating that this practice can eventually lead to soil K depletion in the absence of fertilizer application. Therefore, even though an immediate response was not observed, results suggested that K fertilizer must be used in this system to avoid depletion of Kne.