Developing Nitrogen and Potassium Recommendations for Potato Production in the Columbia Basin Based on Mid-Season Petiole Sampling.

The Columbia Basin (CB) has an ideal climate for potato production and optimum regional yields range from 78-112 t/ha.   Potatoes have high nutrient requirements, up to 504 kg N/ha and 673 kg K/ha are needed.  Grower practice is to assess nutrient need though petiole and soil analysis.  Chloride applications depress petiole nitrate.  Petiole nitrate therefore may misrepresent crop’s N requirement.  Potatoes are grown under center-pivot irrigation in sandy well-drained soils.   Increased concern about groundwater contamination, paired with the need for efficient nutrient recommendations, drive this research.  Our objective is to improve N recommendations by taking into account anion (Cl) competition. Four-row plots were planted in a RCB design under center pivot irrigation in Hermiston, OR.  Four K products (KCl, K₂SO₄, K₂SO₄*2MgSO₄, KCl+B) were applied at variable rates ranging from 112 kg K/ha to 897 kg K/ha in fall, pre-plant, in-season, and split application.  Petioles were sampled throughout the growing season. Yield, grade, chlorophyll levels, specific gravity, and petiole analysis for 2013 and 2014 will be presented.  In 2013 total yield did not differ by treatment.  Pre-plant KCl treatments and the pre-plant 336 kg K₂SO₄/ha rate yielded more potatoes over 283 g than the untreated control.  Pre-plant KCl treatments, the in-season 224 kg KCl/ha rate, and the pre-plant 336 kg K₂SO₄/ha rate yielded less potatoes between 113-170 g than the untreated control.  All KCl treatments regardless of application timing had lower specific gravities than the control.  K₂SO₄ at 224 kg/ha applied either at pre-plant or in-season also reduced specific gravity.