Potassium and sulfur management of alfalfa; Farmer-driven testing of management methods

Final Report for LNE11-307

Project Type: Research and Education
Funds awarded in 2011: $119,984.00
Projected End Date: 12/31/2015
Region: Northeast
State: New York
Project Leader:
Dr. Quirine Ketterings
Cornell University
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Project Information


Over the past ten to fifteen years, sulfur deposition rates have drastically decreased throughout the northeast region and a crop yield response to sulfur addition is now likely. In addition, although our agricultural soils, especially those with some clay, can supply large amounts of potassium, producers and agricultural advisors are reluctant to eliminate potassium use for alfalfa without some evidence that the extra potassium is not needed, fearing reduced yield and/or winter kill. However, increased costs of potassium fertilizer has more farmers interested in looking at soil and tissue testing as a tool for making potassium management decisions. Both potassium and sulfur are macronutrients essential for crop growth. Producers wanted to know whether sulfur and potassium applied with manure in corn years is sufficient to bridge alfalfa years in rotations and what tools to use to reliably identify if extra sulfur or potassium are needed. For potassium management, three approaches are commonly used: (1) potassium removal, (2) soil test potassium, and (3) potassium saturation-based methods. For sulfur management, tissue testing is the usual recommendation with 0.25% sulfur as the critical value beyond which sufficient sulfur is available. In this project, we analyzed data from 72 on-farm field trials to determine the effectiveness of soil test potassium or potassium saturation in determining if potassium is limiting and we evaluated potassium and sulfur status for alfalfa fields with varying fertility management histories. The evaluation of the sulfur status of New York alfalfa fields showed that 7 of 45 (16%) had tissue sulfur at or below 0.25% and that 20 of 45 (44%) had soil test sulfur of 8 ppm or less, suggesting sulfur deficiencies will increase over time unless additional sulfur is applied. Reflecting the increased awareness and interest in managing sulfur, a new soil sulfur test is now being implemented at a commercial laboratory. The potassium evaluation of the 45 alfalfa fields showed that 21 (47%) had soil test potassium less than 150 lbs K/acre, possibly reflecting the need for additional K, while 53% had sufficient potassium. The work on potassium resulted in a new test for measuring cation exchange capacity (CEC) and determination of potassium saturation. Results of the project were presented at crop advisor and field crop dealer meetings and through extension publications.


While potassium fertilizer cost has decreased from the all-time high of $0.80/lbs in 2008, potassium remains an expensive macro-nutrient (about $0.50/lb in most recent years). Alfalfa is a large remover of potassium (about 56 lbs K2O per ton DM). If we assume an alfalfa forage production of about 500,000 acres and yield of 3.8 tons of dry matter per acre (based on 2014 data for NY reported for alfalfa hay and haylage by the National Agricultural Statistics Service; http://www.nass.usda.gov/Quick_Stats/Ag_Overview/stateOverview.php?state=NEW%20YORK), crop removal amounts to 106 million pounds of K2O. If this potassium had to be returned to the soil as fertilizer K, it would, assuming a potassium cost of $0.50/lb, represent a price tag exceeding $53 million dollars.

Potassium removed by crop harvest can be “returned” with manure and/or fertilizer or be supplied by the soil. Soil potassium supply is large for clay soils and fairly low for sandy soils, but all soil will supply potassium to crops as soil minerals weather (break down) over time, reducing the need for potassium supplementation from manure or fertilizer. Manure, when applied to meet N needs for corn in a corn-alfalfa rotation, supplies large amounts of potassium during the corn years, increasing soil test potassium levels, which benefits the alfalfa in the following years, and many dairy producers are comfortable with potassium levels going into the first couple years of alfalfa in the rotation. However, producers and agricultural advisors are reluctant to not use potassium fertilizer for older (3rd, 4th year) alfalfa stands out of concern for reduced yield and/or winter kill.

Sulfur is also an essential macronutrient for crop production. It is a key nutrient in nitrogen fixation so sulfur deficiency can result in both reduced yield and reduced crude protein levels, impacting both overall home-grown forage production and forage quality. This in turn can increase the need for feed imports which will negatively impact both farm profitability and long-term sustainability of the farms. Sulfur can be supplied through mineralization of crop residues, compost, manure, and soil organic matter, sulfur deposition, and sulfur containing fertilizers such as ammonium sulfate (24% S), gypsum (19% S), potassium sulfate, and potassium-magnesium sulfate (both 18% S). In past studies conducted in the ‘80s in the Northeastern United States, sulfur supply from soil organic matter and sulfur deposition were sufficient to meet crop sulfur requirements. However, sulfur deposition has declined over time to now less than 10 lbs/acre. Given an average sulfur removal rate of about 20 lbs/acre for alfalfa in NY (over 30 lbs/acre for high producing fields), sulfur supply from deposition alone is no longer sufficient to meet crop sulfur requirements. This may especially be of concern for coarse-textured (sandy) soils low in organic matter (OM) as such soils have a limited soil organic sulfur reserve. Manure addition could alleviate a potential sulfur deficiency but applications above 4000 gallons/acre per cut could pose phosphorus accumulation problems and other management challenges, including burn and smothering of the stand; such a 4000 gallon/acre application is expected to supply 4 to 8 lbs of sulfur per acre depending on sulfur content of the manure and sulfur availability, possibly enough for crop sulfur needs that year but insufficient for future years unless annual applications are done.

Producer questions addressed in this project are: (1) are potassium and sulfur applied with manure in corn years sufficient to bridge alfalfa years in the rotation, and (2) what tools could be used to reliably identify if extra potassium and/or sulfur are needed. For potassium management, three approaches are commonly used in New York: (1) potassium removal, (2) soil test K, and (3) potassium saturation-based methods. For sulfur management, until recently, tissue testing was the only tool recommended.

We conducted research with funding from both the New York Farm Viability Program, Federal Formula Funds, and NESARE a statewide project to (1) test the different approaches to potassium fertilizer management currently applied across the region (potassium removal, soil test potassium, or potassium saturation based on cation exchange capacity of the soil); and to evaluate the potassium, sulfur and micronutrient status of later year alfalfa stands (3rd-4th year stands).

Performance Target:

Our objectives and performance targets stated that of the six participating farms, four will re-examine their potassium management and reduce production costs by $100/acre or more. Of the 25 farms that evaluate two alfalfa fields each in years 2 and 3, 15 will re-examine their fertility management, leading to potassium use reduction of 50 lbs K2O/acre (redistribution of manure, reduction of fertilizer use). Of 60-80 trainees in the on-farm workshops, a minimum of 10 will become actively involved in on-farm experimentation by year 4 of the project. And, of 300 farmers surveyed in year 4, 30% will express intentions to fine-tune K2O and sulfur use in the next 1-3 years. This is expected to lead to a reduction of potassium use of 50 lbs K2O/acre on at least 25% of all alfalfa acres (taking into account some acreage will need more potassium than is currently supplied), resulting in an estimated total statewide cost savings of $3.4 million or more. The New York State statistics on potassium fertilizer use in 2009-2011 amounted to 21 lbs K/acre, reflecting a 34% decline from an average of about 30 lbs K2O/acre in 1997-2002 and a 22% decline from the average of 25 lbs K2O/acre in 2003-2008. Although the lower potassium use in 2009-2011 reflects a drastic reduction in potassium fertilizer use in 2009 following a sharp increase in potassium fertilizer prices, the overall trend reflects a decline in potassium applications in recent years compared to potassium use 10-15 years ago. The potassium application rates to alfalfa fields are typically considerably higher than for other crops but agricultural statistics does not allow us to identify actual application rates for individual crops and unfortunately, more recent potassium sales data are currently unavailable. Of the farm fields in the study, fields with more grass than alfalfa did not respond to addition of potassium while for fields with more than 50% alfalfa, a response was likely when the soil test potassium levels were less than 150 lbs K/acre. Almost 50% of the fields in the statewide assessment showed the need for potassium and more than 40% showed the potential for sulfur deficiencies in future years, pointing to the need for tools for sulfur and potassium management (soil and/or tissue testing and on-farm experimentation). Talks that reached over 800 attendees and numerous extension publications created greater awareness of the need for potassium and sulfur management and a commercial laboratory is now implementing the new soil test package for sulfur and cation exchange capacity for use by farmers in future years.


Click linked name(s) to expand/collapse or show everyone's info
  • Dr. Jerry Cherney
  • Karl Czymmek


Materials and methods:

On-farm trials were conducted to evaluate the need for potassium fertilizer addition for alfalfa. Each on-farm trial consisted of a “with and without potassium comparison”, conducted for two years with typically 3 or 4 cuttings per year. Each field received two treatments repeated four times: 1) no potassium; and 2) fertilizer potassium applied at a rate of approximate total annual expected crop removal (350 pounds of 0-0-60). We conducted yield estimates, did tissue testing for potassium and S, determined stand composition after two years, and evaluated soil test potassium levels. Statistical analyses (analyses of variance) were done to determine if a field was responsive to potassium and if potassium addition impacted stand composition, while regression analyses were done (using all sites) to evaluate the impact of initial soil test levels on field responsiveness to potassium addition. In addition, we invited farmers to submit forage and soil samples of two fields per farm, generating a 45 field database (across the state; two fields per farm except for one farm where we received samples for one field only). This set of samples (forage and soil) was analyzed for soil fertility parameters, and forage yield and quality. We used the data to conclude the prevalence of potassium and sulfur deficiencies based on tissue testing and/or soil testing data. We tracked potassium fertilizer use based on information supplied by the New York State Department of Agriculture and Markets (through 2011). Training sessions were given for farmers and farm advisors, increasing farmer awareness of the need for potassium and sulfur and tools to evaluate if additional potassium and sulfur are needed, and two undergraduate student interns, along with the collaborating farm advisors, gained experience in conducting on-farm research.

Research results and discussion:

  • Five farmers and one research station, working with farm advisors and campus staff, will host on-farm trials (plus K, no K) on six fields per farm, in 4 replications per farm, for 2 years (for a total of 72 trials).

Accomplishments: A total of 72 trials were completed. The fields consisted of six fields per farm on six farms, conducted for two years. All samples collected in the field (yield, quality, soil fertility) were analyzed in the laboratory and results were used to determine crop responsiveness to potassium addition. In addition, trials with additional treatments (potassium and sulfur combined) were completed at three other locations, including a farm in western NY, and research stations in central and eastern New York. The results of these trials showed no benefit of application of calcium (to reduce potassium levels) on yield or forage quality, field responsiveness to potassium when the alfalfa stand had at least 50% alfalfa (no response to potassium when it was a grass-dominated stand), no impact of elimination of a potassium addition on stand composition, and a likeliness of a crop response to potassium when the Cornell soil Morgan extractable potassium levels exceeded 150 lbs K/acre, consistent with current guidelines for soil of soil management groups 3 and 4 (3 = moderately coarse-textured soils developed from glacial outwash and recent alluvium and medium-textured acid soils with fragipans developed on glacial till, mostly silt loam soils; and 4 = coarse- to medium-textured soils formed from glacial till or outwash, mostly sandy loam soils).The dataset was used to evaluate a more accurate way to determine potassium saturation and cation exchange capacity and those results were published in a recent journal article. The new tests are currently being implemented in two different commercial laboratories. The tissue test data showed that for sulfur, tissue testing with a critical tissue sulfur level of 0.25% (i.e. higher than that, no need for additional sulfur; less than that, addition of sulfur can result in crop yield increase) is recommended. For potassium, tissue testing was not a reliable predictor for crop responsiveness to potassium addition.

  • In addition, 25 farmers will evaluate two fields per farm (farmer selected) for K, sulfur and micronutrient status (years 2 and 3) using an effective combination of tissue and soil testing.

Accomplishments: In total, 23 farmers submitted samples for analyses for potassium and S, resulting in a dataset of 45 fields (one farm submitted one field only; all others submitted two fields per farm). These samples were analyzed for soil fertility status and for yield and forage quality indicators and results were reported for all 45 fields together. The results showed 7 of all 45 fields (16%) had tissue sulfur at or below 0.25% and 20 of 45 (44%) had soil test sulfur of 8 ppm or less, suggesting sulfur deficiencies will increase over time unless additional sulfur is applied. Work on potassium showed that 21 of 45 (47%) had soil test potassium less than 150 lbs K/acre, possibly reflecting the need for additional potassium while 53% had sufficient K. As mentioned, the work on potassium resulted in a new test for measuring cation exchange capacity and for determination of potassium saturation (and magnesium and calcium saturation). The latter could be used to determine if a crop response to additional potassium is likely but the Cornell Morgan soil test potassium was a more reliable predictor of the need for extra potassium, as long as the stand was 50% or more alfalfa (no potassium response for fields that were primarily grass). However, most illustrative of a need to better evaluate alfalfa fields, was the fact that 60% of all fields has a soil pH below 6.7, the pH at and below which lime addition is recommended.


  • In year 2-3, 60-80 farmers and farm advisors will be trained in on-farm research, through participation in four on-farm workshops, and have the tools to conduct on-farm testing.

Accomplishments: The new tools developed as part of this project included the new Cornell soil sulfur test and the cation exchange capacity test (and related potassium, calcium and magnesium saturation levels). Through presentations at grower meetings, demonstrations at extension field days, and winter and summer crop advisor meetings in the past years, we shared the trial design and project results with over 800 people. In 2011, 14 farm advisors were trained through hands-on experience in on-farm research, specifically this trial on the effect of potassium addition to yield, tissue potassium and S, and soil sampling. In addition, approximately 30 farm advisors (Certified Crop Advisors) attended the on-farm research partnership presentation at the Northeast Region Certified Crop Adviser training on December 1, 2011, the session on adaptive management at the 2012 Northeast Region Certified Crop Advisors Annual Training held on November 28, 2012 in Syracuse, NY, while 98 people attended trainings offered by the Capital District Agriculture and Horticulture Program (CCE) on improving your business with on-farm research in Latham, NY (December 18, 2013).


  • Of all alfalfa growers, 60% will become aware of the existence and results of the project by year 4 (through work with consultants, extension and farmers and extension and popular press articles). Of these farmers, 300 will be surveyed (postcard survey) for intent to use project results to evaluate potassium management at home, in year 4 of the project.

Accomplishments: Research findings were published in extension articles and journal articles. Three journal articles co-sponsored by the NESARE project included: (1) Ketterings, Q.M., S. Gami, R.R. Mathur, and M. Woods (2014). A simple method for estimating effective cation exchange capacity, cation saturation ratios and sulfur across a wide range of soils. Soil Science 179:230-236; (2) Ketterings, Q.M., G. Godwin, S. Gami, K. Dietzel, J. Lawrence, P. Barney, T. Kilcer, M. Stanyard, C. Albers, J.H. Cherney, D. Cherney, K.J. Czymmek (2012). Soil and tissue testing for sulfur management of alfalfa in New York State. Soil Science Society of America Journal 76(1): 298-306. (doi:10.2136/sssaj2010.0437); and (3) Ketterings, Q.M., C. Miyamoto, R.R. Mathur, K. Dietzel, and S. Gami (2011). A comparison of soil sulfur extraction methods. Soil Science Society of America Journal 75(4): 1578-1583. Talks were given on sulfur and potassium (and pH!) management and on-farm research (and adaptive management, the term used by the Natural Resources Conservation Service). This included a summary talk on alfalfa potassium and sulfur management at the Field Crop Dealer Meetings in Syracuse, November, 2014, at the Valatie Research Farm field day in August, 2014, and at the winter meeting of Helena Inc. in Albion, NY in December of 2014. These and other talks (see complete list below) were attended by about 870 people. In addition, public press articles were written and four agronomy factsheets were developed: (1) # 66: Cornell Sulfur Test for Alfalfa (3/17/2012); (2) # 68: On-Farm Research (7/9/2012); (3) # 69: Adaptive Nutrient Management Process (7/22/2012); and (4) # 83: Gypsum for Field Crops in NY (12/20/2014). Two student interns learned about potassium and sulfur management and on-farm research through interactions with consultants and extension educators. For the experience of one of the students, see: http://nmsp.cals.cornell.edu/publications/impactstatements/DiegoGris.pdf. In addition, “What’s Cropping Up?” field crop extension articles were written and shared on our Cornell Nutrient Management Spear Program website (Ketterings, Q.M., G. Godwin, S. Gami, K. Dietzel, J. Cherney, and K.J. Czymmek (2012). Sulfur for alfalfa in New York State. What’s Cropping Up? 22(2): 12-16; Ketterings, Q.M., G. Godwin, J. Cherney, and K. Czymmek (2011). Effect of manure, compost and potassium application on alfalfa yield, potassium content, and soil test potassium in Aurora, NY. What’s Cropping Up? 21(4): 8-12; and Ketterings, Q.M., G. Godwin, J. Cherney, and K. Czymmek (2011). Comparison of tissue and whole plant potassium for alfalfa. What’s Cropping Up? 21(4): 13-15; all articles are accessible at: http://nmsp.cals.cornell.edu/publications/extension.html).

Participation Summary


Educational approach:

Talks given include:

  1. Ketterings, Q.M. (2015). Alfalfa field revisited. Soil pH, sulfur potassium and
    cation exchange capacity. Southern Tier Crop Congress. Belfast, NY. January 9, 2015. 45 min. ~35 people.
  2. Ketterings, Q.M. (2014). Sulfur management. Helena winter grower meeting. Lyndonville, NY. December 12, 2014. 25 min. ~60 people.
  3. Ketterings, Q.M. (2014). Alfalfa field revisited. Soil pH, sulfur and
    cation exchange capacity. Field Crop Dealer Meetings. Syracuse, NY. November 12, 2014. 30 min. ~80 people.
  4. Ketterings, Q.M. (2014). Sulfur and potassium management of alfalfa. Valatie Research Farm Field Day. August 19, 2014. Valatie, NY. 20 min. ~35 people.
  5. Ketterings, Q.M. (2013). Soil testing and plant analyses. Northeast Region Certified Crop Advisor Annual Training. Basic Training. December 4, 2013. Syracuse, NY. 45 min. 32 people.
  6. Ketterings Q.M. (2013). Sulfur management for field crops. Mid-Atlantic Region Certified Crop Advisor conference. November 21, 2013. Ocean City, Maryland. ~50 people. 1.3 hours.
  7. Ketterings Q.M. (2012). NY On-Farm Research Partnership: Working together on research for greater impact at farm and state levels. Capital District Agriculture and Horticulture Program (CCE); Improve Your Business with On-Farm Research (Winter Meeting). Latham, NY, December 18, 2013. 45 min. ~25 people.
  8. Ketterings Q.M, and K.J. Czymmek (2012). Adaptive management for corn. 2012 Northeast Region Certified Crop Advisors Annual Training. November 28, 2012. Syracuse, NY. 2x50 min. 73 CCAs.
  9. Ketterings, Q.M. (2012). Soil testing and plant analyses. Northeast Region Certified Crop Advisor Annual Training. Basic Training. November 28, 2012. Syracuse, NY. 45 min. 23 people.
  10. Ketterings, Q.M. (2012). Sulfur needs of alfalfa; tools for management. Joint Meeting of the Regional Soil Testing Workgroups North Central region (NCERA-13), Southeastern region (SERA-6), and Northeastern region (NECC-1012), Madison, WI, August 27-29, 2012. 30 min. ~70 people.
  11. Ketterings, Q.M., and K.J. Czymmek (2012). Sulfur management of alfalfa. Joint North American Alfalfa Improvement Conference/Trifolium Conference/Grass Breeders Group. July 13, 2012. ~100 people. 15 min. Invited talk.
  12. Ketterings Q.M., K. J. Czymmek (2011). New York State on-farm research partnership. Northeast Region Certified Crop Advisor Annual Training. November 29-December 1, 2011. Syracuse, NY. 50 min. ~40 people.
  13. Ketterings, Q.M., K.J. Czymmek (2011). New York State potassium for alfalfa project - results of the statewide project. Northeast Region Certified Crop Advisor Annual Training. November 29-December 1, 2011. Syracuse, NY. 50 min. ~80 people.
  14. Ketterings, Q.M. (2011). Soil testing and plant analyses. Northeast Region Certified Crop Advisor Annual Training. Basic Training. November 29-December 1, 2011. Syracuse, NY. 45 min. ~33 people.
  15. Ketterings, Q.M. (2011). Can New York farmers afford to manage alfalfa without sulfur addition? 2011 Field Crop Dealer Meetings. November 21, 2011. Multiple locations. 35 min. ~133 people.

Written documents (factsheets and extension articles) were already described in this report. A project website listed the protocols we used for the field assessment project (http://nmsp.cals.cornell.edu/NYOnFarmResearchPartnership/KandSAlfalfa.html).



No milestones

Additional Project Outcomes

Project outcomes:

Impacts of Results/Outcomes

It was difficult to document impact on fertilizer sales due to changes in the reporting system in New York State. Current records include annual sales through 2011. The 2012 data were shared with us but we found issues with the way results were reported and are currently working with the state to try to get these issues resolved. Thus, we were able to document a decline in potassium fertilizer sales in 2009-2011 compared to earlier years but do not have records from 2012-2015 yet. We will continue to collect and evaluate sales data as they become available. The real success of the project is in the interest among farmers and farm advisors as well as laboratories in the new Cornell sulfur test and the cation exchange capacity test and increased awareness of the need to test soils, and for sulfur tissue as well, for making management decisions. We are currently working with DairyOne to implement the new soil test sulfur and cation exchange capacity tests for use in alfalfa in New York, initiated by the interest of crop consultants. The western New York farm had requested the addition of a calcium treatment to see if forage quality was impacted by calcium addition. The farm’s data showed no benefit of calcium addition and the farm decided to move forward with potassium additions where soil test results indicated the need for potassium.

Economic Analysis

The results of the assessment of the 45 farmer fields suggested that sulfur deficiencies exist in New York State and that a considerable number of fields will not need extra potassium (while others do), and that assessment of sulfur status of crops could help increase yield and quality. Perhaps at least as important this work showed that many fields are being managed at a pH too low for any soil or tissue testing tool to be a reliable indicator for crop needs. These findings re-emphasized the need to focus on pH management first, and then to follow with sulfur and potassium management. Talks were adjusted to include slides on the importance of pH management which will benefit farm operations in the future.

Farmer Adoption

The experience of farm advisors and the farmer in western New York were documented in: http://nmsp.cals.cornell.edu/publications/impactstatements/CoyneKproject.pdf. A quote from the farmer featured in this story, “My driving interest in this research project was to find a way to reduce potassium levels in the alfalfa forage we feed to the cows. I am hoping we can find the level that keeps the crop healthy and productive while having manageable levels of potassium for the feeding program.” The findings were that addition of calcium did not improve forage quality and illustrated that avoidance of over-application of potassium should be the primary target. The latter can be done based on soil analyses. In addition, the farmer said: “It’s been excellent having the staff here at the farm. They are approachable without taking up my work time. It’s very exciting to see the research going on right here in my fields.” Larger scale farmer adoption was difficult to document due to lack of more recent fertilizer sales records. A great achievement of the program is the development of a new soil test package and the fact that the new test package is currently being implemented in a commerical laboratory indicates farm advisor and farmer interest in making soil testing for sulfur and cation exchange capacity part of the regular assessment of alfalfa fields. The potential for gains in yield (where potassium and/or sulfur deficiencies exist) or savings in fertilizer costs (where soil contains sufficient amounts of potassium and/or sulfur) in futurre years will need to be documented.

Assessment of Project Approach and Areas of Further Study:

Areas needing additional study

As mentioned, the new Cornell soil sulfur test and cation exchange capacity test package is currently being implemented at the DairyOne soil testing facility for use by New York farmers. Analyses can also be requested from the Nutrient Management Spear Program (until the moment that the DairyOne laboratory can offer the same test with the same quality). Our work to date has focused on alfalfa and mixed alfalfa/grass stands. Reports, especially this spring and early summer, of widespread sulfur deficiencies for corn (striped corn, young leaves) point toward the need to also evaluate the new tests for use in corn and other crops. Future work is needed on sulfur and potassium needs of corn, in addition to expansion of awareness of the availability of new tools for sulfur and potassium testing.



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Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.