Productivity of Sugarcane with Thermopotash (FIRST HARVEST).

Verdete is a silicate rock rich in glauconite and its K₂O percentage is between 7 and 11%. Mixing Verdete with CaCO₃ and heating to 1100 °C produces the thermopotash, an insoluble source of potassium in water. This study evaluated the effect of thermopotash in sugar cane production. An experiment with cultivar SP832847, was installed in June 2011 in Energy Cia Vale do São Lourenço, Minas Gerais, Brazil. The soil was  classified  as  Rhodic Acrustox, with  the  following  characteristics: pH 4.4; 15 mg dm^-3 K; ECC 3.4 mmol_c dm^-3. The experimental design was a randomized block in 2x5 a factorial arrangement Two sources of potassium were potassium chloride with 60% K₂O, and thermopotash with, 7.0% K₂O, 28.4% Si, 31% CaO and 6.9% MgO. Potassium doses were: 0, 100, 150, 200 and 250 kg ha^-1, totaling 10 treatments  with  5  replications. Each plot was five 20-m long rows spaced at 1.5 m, with  a  total  area  of  ​​150 m².  In sugarcane planting 250 kg ha^-1 of monoammonium phosphate was applied along  with  treatments at  the  bottom  of  the furrow. One year after planting sugarcane harvest and productivity  was  determined.  Both  KCl  and  thermopotash  increased productivity of sugarcane independent of potassium dose used, which can be adjusted by the equation y = -0.0012x²+0.2905x+115.03, R² = 78%. When the cane did not received K fertilization the productivity was 113.3 t ha^-1; in contrast with addition of potassium, regardless of the source used, maximum yield was 132.61 t ha^-1, with the application of 121.04 kg ha^-1 K₂O. Thermopotash can be used as potassium fertilizer because, although not statistically significant, it showed a average increase at 5 t ha^-1 compared to KCl. Acknowledgement: Fapemig