Potassium Status Evaluation Using Real Time X-Ray Fluorescence on Sugarcane.

Potassium is a key nutrient required in high quantities in sugarcane, an important crop for Brazil’s economy. Therefore, it is important to assess foliar nutritional status based on real time and non-destructive methods. The objective of this study was to evaluate the potential of application of X-ray fluorescence (XRF) for determining potassium foliar composition on sugarcane amended with two potassium fertilizers. Greenhouse experiment was conducted with sugarcane (Saccharum ssp. cultivar. CV7870) using a Quartzipsamment, arranged in a completely randomized design with K, Ca, Mg, S sources; four dosages of potassium (0, 50, 100 and 150 kg K₂O ha^–1) using polyhalite (POLY4) and potassium muriate (MOP) combined with phosphogypsum and kieserite, balancing Ca, Mg and S, supplied by POLY4, to reach the dosages evaluated. Hand-held XRF scans were performed on the diagnostic leaf to measure K and other nutrients intensities at 90 days after transplanting (DAT). The intensity was correlated with nutrient content in foliar tissue determined by chemical analysis at 90 DAT. Additionally, a laboratory study using µ-XRF spectroscopy was carried out on POLY4 and MOP granules to observe the spatial distribution of the elements. The results showed that K, Ca and S intensities were influenced by dosage (p<0.05), presenting similar trend as chemical method. Biomass and soil nutrient concentrations showed that K and S from POLY4 were as effective as MOP in terms of their availability to sugarcane. The granule of POLY4 showed that S is located all over the analyzed granule area, whereas K, Ca and Mg are distributed in spots, possibly complexed by S, and MOP presented high intensities of Cl and K in the analyzed region. Thus, the results indicated that XRF could be used in situ for foliar nutrient analysis and the diagnosis of potassium status in sugarcane.