2018 ASHS Annual Conference

Polyhalite (PH) is a naturally occurring multi-nutrient fertilizer containing 14% K₂O, 17% CaO, 6% MgO, and 19% sulfur. We recently reported the positive response of tomato (Solanum lycopersicum L.) to PH, in comparison to muriate of potash, sulfate of potash (SOP), and potassium magnesium sulfate (SOPM) from two rate response trials in Sao Paulo state, Brazil. However, PH as a sole K source exceeds crop S requirement and there is a need to determine its appropriate inclusion rates. The current study evaluated SOP, SOPM, SSP (single super phosphate) and PH as S sources, each supplying a 40 kg S ha^-1 at three sites. Uniform K rate was ensured for the above treatments by varying MOP application rates. There were two control treatments, one did not contain K and S (KS control), and the other one contained K but not S (S control). All treatments received constant N and P rates. Yield, quality, foliar and fruit nutrient data was collected and analyzed by ANOVA in JMP software. Sources and rates were defined as fixed and random factors, respectively and the blocks were nested in site. Tukeys means separation procedure was used at 10% significant level. Pre-trial soil pH was 5.3, and soil K ranged from 61 to 83 mg kg^-1, soil Ca ranged from 250 to 266 mg kg^-1, and soil Mg ranged from 70 to 82 mg kg^-1. Only PH treatment increased total and marketable yields and fruit numbers compared to KS control which could be explained by the multi-nutrient composition of PH. In general, ascorbic acid, titratable acidity, and fruit pH were lower in the KS control compared to all other treatments. Fruits from all treatments were found to be similar for brix and firmness. Foliar K concentration was lower in KS control than all other treatments and foliar P concentration was lower in both KS and S controls than SSP, while both PH and SSP resulted in higher foliar S concentration than KS and S controls. Interestingly, KS control resulted in higher foliar Ca concentration than all other treatments except PH, possibly be due to lower competition between potassium and calcium in KS control and PH treatments. Consistently increased total and marketable yield for PH confirms its usage as a potential multi-nutrient source in Sao Paulo state of Brazil for tomato cultivation.