Evaluation of Polyhalite As a Fertilizer in Comparison to Sulphate of Potash for Tobacco.

Polyhalite (K₂SO₄.MgSO₄.2CaSO₄.2H₂O) can potentially expand the  option of low chloride potash sources for tobacco. In order to evaluate the product, two replicated, RCB trials were conducted at Xundian Daheqiao farm, Yunnan Agricultural University in successive years. Recommended fertilizer amount for the local variety,  YN87 (RF) is 105kg N/ha, and N: P2O5: K2O = 3:1:5 in Xundian county, Yunnan province. N and P fertilization levelswere fixed at  the RF, Ammonium phosphate nitrate (30-6-0) and Diammonium phosphate (18-46-0) were used as N and P fertilizers for this experiment. Potassium fertilizer was either polyhalite or SOP was applied at rates, 0, 1/2 RF, 2/3 RF, 1 RF and 3/2 RF.

For 2014 the crop demonstrated a quadratic yield response to potassium fertilizer. Potash sources did not respond significantly differently, although the polyhalite fed crop gave numerically higher yields. Crop output financial value also responded significantly to potash application, products were not significantly different; however, polyhalite supported a numerically higher value. Black shank disease incidence and disease index were significantly reduced under polyhalite compared to SOP, however, the reverse was true for bacterial wilt .

During 2015, no significant differences for the maximum leaf length, maximum leaf width, plant height, leaf number, stem girth and pitch were observed. A rate response to potassium was observed. Polyhalite supported a numerically greater yield and estimated crop financial value, but the differences were not statistically significant. Bacterial wilt disease incidence and disease index were not different over the K rates  ½ to 1 RF, but were at 3/2 RF.

In use, polyhalite fertilizer recommendations may follow the SOP to rates in support of yield and quality.