December 2015 Newsletter - #47  
In This Issue

Read the latest posting: 
Corn Silage Harvested in 2015 - Part 2 
Soil and Manure Potassium Levels
from 2010 to 2015

Sally Flis, Ph.D. - Feed and Crop Support Specialist - Dairy One

Potassium (K) levels in the soil and in crop nutrition has come up at meetings and in conversations a lot this year. This led me to look into our soil testing and manure testing results. In the Agro-One lab, we perform the Mehlich-3, Modified Morgan's, and Morgan's extraction for testing nutrient levels in soils.

Figure 1. Soil test K results by extraction from 2010 to 2015 from the Agro-One Lab.

Over the last 6 years, the average soil test K level has been high and has remained high for all 3 soil test extractions. The 6 year average for Morgan's was 213.4 lbs/ac K, for Modified Morgan's was 221.0 lbs/ac, and for Mehlich-3 was 241.2 lbs/ac. There is no trend for either increasing or decreasing soil test values. However, the standard deviation of all the extractions was almost equal to the average, indicating a very large range in sample results.

In order to get a better representation of the K status of soils we have tested, Table 1 shows the percent of samples that resulted in a recommendation of no K application for the crop. The Mehlich-3 extraction has the highest percentage of samples that would be recommending K application for crop production, this is also the largest percentage of samples that come into the lab. On average over the last 6 years, 63.3% of the samples submitted to the lab were for Mehlich-3 analysis. The Modified Morgan's extraction averaged 18.6 % and the Morgan's averaged 18.1% of samples per year over the last 6 years.

*In NY, soil test K levels are interpreted by soil management groups; this is the lowest of the high values for soil management group I.   Cornell K Guidelines .

After seeing the high soil test levels, I also looked at the manure K values for the last 6 years. The average book value for liquid dairy manure K2O lbs/1000 gal is 20. In Table 2 are the average results for samples submitted to the lab and identified as Manure, cow liquid. These numbers are all lower than the average book value.

In conversations this year, I heard concerns that producers are seeing K deficiency problems. After examining the data from the Agro-One lab, here are a few thoughts on the discussions regarding K deficiency concerns in field crops:
  1. The majority of the samples we test would recommend some K application for crop production.
  2. Our average manure K test values are lower than book values.
  3. What values are being used for manure applied to crop field for K level?
  4. Are individual field balances done when determining K application?
If you are suspicious of a K nutrient problem, looking into the field history, nutrient application, and adding tissue testing to the management plan will help to pinpoint needs for management to address.
Where to Find Us in January 2016

Meeting Name
Date for 2016
January 3 - 7
Philadelphia, PA
January 8 - 9
Islip, NY
January 11 - 13
St. Louis, MO
January 18 - 20
Savannah, GA
2016 Penn Ag Education Conference
January 21 - 22
State College, PA
January 30 - February 3
Reno, NV

Reminder: Holiday Forage and
Agro-One Lab Closings

With the upcoming holidays, the Forage Lab and Agro-One Lab will be closed Friday December 25th, and Friday January 1st. Please plan ahead for submitting your samples and receiving results. 
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Dairy One - Forage Laboratory
730 Warren Road ~ Ithaca, NY ~ 14850
Phone:  1-800-344-2697 Ext. 2172