Effect of Polyhalite As a Source of Potassium and Sulfur on Crop Yields and Nutrient Uptake.

Polyhalite, K₂MgCa₂(SO₄) is potentially, a multi-nutrient fertilizer source for crops grown in S and K deficient soils. Its impact on field crops, as a K and S fertilizer source, has had mixed reviews that are sometimes attributed to slow release of K. A study was conducted at Carrington, ND to assess the relative impact of polyhalite K and S fertilizer on agronomic performance of corn, yields, and the soil residual nutrient content before planting and fertilization, and after harvest. The treatments were: 20 and 40 kg/ha of K, applied as polyhalite, muriate of potash (MOP), MOP + ammonium sulphate (AMS), MOP+gypsum, and microessentials (MES10 and MESZ), plus two checks (0 kg K/ha added) with or without S. All but MOP treatments received 67 and 136 kg of S at 20 and 40 kg K, respectively. Corn growth parameters did not show significant response to K fertilizer treatments. Yields showed significant response to K rates (p<0.0174), K source (p<0.0453), and S rates (p<0.0111). Mean yields increased from 20 kg K rate to 40 kg K. This trend was observed for MOP and MOP+AMS, meanwhile yields dropped at the higher K rate for MOP+gypsum, MES10, and MESZ. Ear leaf analysis showed significant effect of K source on the P (p<0.0081) and Zn (p<0.0361) content. MES10 treatments had the highest leaf P content, which was expected given additions of at least 107 kg of P₂O₅ to the soil that was already high in P. The lowest leaf Zn was recorded for MES10 and MESZ’ probably because of the antagonism that exists between P and Zn in soil. Current results suggest that yields and protein had similar response to polyhalite and MOP.