January 2021

K-Mag® Onion Blend Study


Evaluate onion marketable yield response to MAP (11-52-0), MAP + MOP (0-0-60) and MAP + MOP + K-Mag® Premium (0-0-21.5-10.5Mg-21S).


  • Phosphorus (P), along with potassium (K), magnesium (Mg) and sulfur (S) are macronutrients needed for a balanced crop nutrition program in onions.

  • Magnesium is critical for photosynthesis, increased dry matter, heat-stress tolerance, disease resistance, and crop quality.

  • Ensuring K, Mg, and S availability through bulb development can be difficult on coarse, well-drained sandy soils.

  • K-Mag is a unique 3-in-1 nutrient source that features low chloride, water soluble nutrients, and does not affect soil pH; regardless of application rate.


Crop: Onion (Allium cepa)

Years: 2019-2020

Locations: 4 trials across the following states - ID, WA

Data Source: Field studies conducted by third-party, independent researchers.

Experimental Design: Small-plot RCBD with 4 replications.

Cropping Conditions: All trials conformed to local cropping practices.


Treatment (Trmnt) / Rates / Timing:

  1. N Rate: Applied according to local recommendations

  2. P Rate: 100 lbs P₂O₅/ac applied as MAP

  3. K Rate: 120 lbs K₂O/ac applied as either MOP or a blend of MOP (90 lbs K₂O/ac) + K-Mag (30 lbs K₂O/ac)

  4. Application Timing: Preplant

Application Method: Broadcast Incorporated


K-Mag® Onion Blend Study - Results


  • Addition of MOP increased onion yield 6 cwt/ac compared to MAP only.

  • Replacing a small amount of MOP with K-Mag (30 lbs K₂O) increased onion yield by 26 cwt/ac over MAP + MOP. These results demonstrate the value of K, Mg, and S for a balanced crop nutrition program in onions.

  • Access additional yield data, technical information, and resources at KMag.com/Performance.

©2021 The Mosaic Company. All rights reserved. AgriFacts and K-Mag are registered trademarks of The Mosaic Company.

Individual results may vary, and performance may vary from location to location and from year to year. This result may not be an indicator of results you may obtain, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible. For more information, go to Kmag.com.