February 2019

Aspire® Alfalfa Timing Study


Evaluate the alfalfa yield response of various treatments and application timings of MOP (0-0-60), an MOP + Granular B blend, and Aspire® (0-0-58-0.5B).


  • Alfalfa removes high rates of potassium (K) from the soil, so MOP is commonly used as a K source to replace nutrient removal.

  • In addition to K, adequate soil boron (B) is needed to achieve maximum yields (Figure 1).

  • Granular B products can be blended with K, but application of these blends often leads to undesirable distribution.

  • Aspire® is a superior B delivery source that combines K with two forms of boron for both early- and late- season needs.

  • Additionally, application timings vary across producers (often driven by weather and logistics), so it is important to understand crop responses with different management approaches.


Crop: Alfalfa (Medicago sativa)

Years: 2017–2018

Locations: 6 trials (Columbus, WI; Cambridge, WI; and Deford, MI)

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

Experimental Design: Small-plot RCBD with 4 replications.

Cropping Conditions: Trials conformed to local cropping practices and were conducted on an established stand.


Treatment (Trmnt) / Rates / Timing:

Numbered and color-coded to match bar chart. All treatments received a total of 240 lbs K₂O/ac. Trtmnts 2-5 received a total of 2 lbs B/ac. Values in ( ) represent lbs K₂O/ac or lbs B/ac

  1. MOP (120) applied after 1st and 3rd cutting of harvest year.

  2. MOP (120) + Granular B (1) blend applied after 1st and 3rd cutting of harvest year.

  3. Aspire® (120/1) applied after 1st and 3rd cutting of harvest year.

  4. Aspire® (120/1) applied fall of previous year. Aspire (120/1) applied spring of harvest year.

  5. Aspire® (240/2) applied fall of previous year.

Application Method: Broadcast

Alfalfa study figure


Alfalfa Yield


  • Alfalfa yields responded positively to the addition of boron.

  • Aspire split-applied after 1st and 3rd cuttings of harvest year increased alfalfa yield 0.8 tons/ac over MOP and 0.5 tons/ac over the MOP+Granular B blend.

  • Split applications (120-Fall/120-Spring) of Aspire® and full-rate fall applications (240-Fall) yielded 0.7 ton/ac and 0.6 ton/ac over MOP, respectively.

  • The results suggest that while applications of Aspire® after 1st and 3rd cuttings of harvest year provide maximum yield, split application (fall/spring) or full-rate fall applications perform almost as well and demonstrate the flexible application window offered by this fertilizer technology.

©2020 The Mosaic Company. All rights reserved. AgriFacts, MicroEssentials, SZ, Fusion, Aspire and NutriForm 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.

WARNING: Contains boron. Use of boron may result in crop injury. DO NOT place this product in direct contact with the seed.