Potato Yield and Dry Matter Response to Different Sources of Potassium Fertilizer in England.

Limited available information pertaining to the performance of polyhalite (14% K2O, 17% CaO, 6% MgO and 19% S) on potato prompted us establishing two trials under loamy soils in Staffordshire, England. All the following treatments received standard N and P nutrients. First trial evaluated three different sources of potassium: Muriate of Potash (MOP), Sulphate of Potash (SOP), and Polyhalite at 0-400 kg of K₂O per hectare supplying different rates of Mg, S and Ca. Each source of potassium resulted in higher tuber yield than the control which recorded 37.4 tons per hectare. No significant differences in either total or marketable yield were observed among different sources of potassium. However, polyhalite recorded 1.2 tons of higher total tuber yield than MOP and SOP which recorded a tuber yield of 48.8 tons per hectare. Polyhalite and control recorded higher dry matter content than MOP treatment.

The objective of the second trial assessed blends of polyhalite and MOP in different proportions performs on par with a practice of meeting total K₂O requirement through MOP. First treatment was standard N and P control, second treatment was Control+Mg, supplied with 80 kg of MgO through Kieserite. Treatments 3 and 4 were applied 300 kg of K₂O from MOP and Polyhalite respectively. Treatments 4, 5, and 6 were dry blends in which  16%, 25% and 62%  of 300 kg K₂O need was met by polyhalite, respectively. The remainder  of the 300 kg K₂O requirement was met by MOP. Treatments 7 and 8 were similar to treatments 4 and 5 but were also supplied Kieserite to meet 80 Kg MgO requirement. No significant differences in tuber yield were observed between control and MOP. However, treatments containing polyhalite in different proportions resulted in significantly higher yield than the controls. Treatment 8 resulted in significantly higher yield than MOP. These two trials indicate the effectiveness of polyhalite both as a straight fertilizer and as a part of blend with MOP to meet the potato nutrient requirements.