2019 ASHS Annual Conference

Yield response of chili peppers (Capsicum annuum L., cv ‘TAM Mild Jalapeño II’) to three potassium fertilizer sources: (i) muriate of potash (MOP; 60% K₂O), (ii) sulfate of potash (SOP, 50% K₂O, 17% S), and (iii) polysulfate (PS; an organic multi-nutrient fertilizer containing sulfur, potassium, calcium and magnesium as 14% K₂O, 17% CaO, 6% MgO and 48% SO₄) were investigated in greenhouse studies (spring and fall 2017) using a local calcareous potting soil. All fertilizer sources were applied at four equivalent K₂O rates (50, 100, 150, and 200 kg·ha^-1). Fruit yield and yield components (average fruit mass, number of fruits per plant, dry matter content) were significantly increased by K fertilization (P<0.001) in both seasons; however, yields were generally higher in the spring study (average 19 mT·ha^-1) compared to fall (average 55.5 mT·ha^-1) possibly due to a relatively shorter growing season and cloudy weather conditions during the fall study. In in both studies, yields were higher for all rates above the 50 kg·ha^-1 rate. Fruit number per plant was higher with PS and SOP than control and MOP treatments. Average seed mass per fruit was increased by fertilization but this was also significant only with SOP and PS treatments at the 150 and 200 kg·ha^-1 rates. Fruit firmness and dry matter content generally increased linearly with K₂O application rates (P<0.01) with a slightly higher responses observed with PS and SOP than with MOP. Post-harvest soil analysis indicated slightly lowered soil pH in PS and SOP treatments and lower sodium concentrations in PS treatments. The results suggest that multi-nutrient fertilizer sources such as PS have potential yield and quality benefits for organic crop production and better nutrient use efficiencies, perhaps due to synergies resulting from different nutrient components.