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

2014 Annual 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

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


Over the past ten to fifteen years, sulfur (S) deposition rates have drastically decreased throughout the region and a yield response to S addition is now likely. In addition, although our agricultural soils, especially those with some clay, can supply large amounts of potassium (K), producers and agricultural advisors are reluctant to eliminate K use for large K consumers like alfalfa fearing reduced yield and/or winter kill but increases in fertilizer prices have people wondering about K needs for their crops.

This year we completed our evaluation of the impact of K addition on forage quality, tissue K and S levels and stand composition at the Aurora Research Farm, the Valatie Research Farm and an on-farm location in western NY with a final sampling round for 1st cutting in 2014. All harvests were completed (2 years of data), soil samples were taken and analyzed, and data are being summarized in final reports for distribution in January.

Consistent with the earlier trends, at the Aurora site, a response to S was clearly visible (much darker colored alfalfa) while a yield response was documented where both S and K were applied. At other locations, no yield benefits were seen although tissue testing was clearly impacted by S addition. 

A total of 23 farms (2 fields per farm for all but one of the farms) were sampled for tissue K and S, soil K and S, yield and forage quality. Initial summary tables were put together and results were shared with the extension educators, consultants and farmers that we worked with. This dataset indicated that 7 of 45 (16%) had tissue S at or below 0.25% (deficient). As we asked farmers to select one field for which they did not expect any deficiencies and one field for which they weren’t sure, the actual percentage of S deficient fields might be much higher. Soil testing showed that 20 of 45 (44%) had soil test S (Cornell soil test) of 8 ppm or less, indicating that in some fields, the plants are not showing deficiencies yet, but that the soil is running out of S. Thus, we expect that more fields will become deficient over time, making it important for farms to sample for S and, more importantly, to experiment with S addition in fields where a S deficiency is expected. The assessment also showed that 24 of 45 (53%) has soil test K exceeding 150 lbs K/acre, possibly indicating the need for better K management. Prior trials had indicated that a crop response when soil test K (Cornell test) exceeds 150 lbs K/acre, a crop response to additional K is not needed. 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.

This year, additional talks were given on sulfur and potassium (and pH!) management and on-farm research (and adaptive management, the term used by NRCS). This included a well-attended talk on alfalfa K and S management at the Field Crop Dealer Meetings in Syracuse, November, 2014 (about 80 people), field presentations at the Valatie Research Farm field day in August (about 35 people), 2014, and at the winter meeting of Helena Inc. in Albion, NY this December (about 60 people).

Objectives/Performance Targets

Of the six participating farms, four will re-examine their K 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 K 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 S use in the next 1-3 years. This is expected to lead to a reduction of K use of 50 lbs K2O/acre on at least 25% of all alfalfa acres (taking into account some acreage will need more K than is currently supplied), resulting in an estimated total statewide cost savings of $3.4 million or more.


Milestone: (1) 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). Progress: We completed all field trials this year, completing the 2-year cycle for the latest trials.

Milestone: (2) In addition, 25 farmers will evaluate two fields per farm (farmer selected) for K, S and micronutrient status (years 2 and 3) using an effective combination of tissue and soil testing. Progress: In total 23 farms were sampled (two fields per farm, soil, tissue, forage). Data were summarized and results were shared with the participating farms and farm advisors, and with the larger extension and farming audiences.

Milestone: (3) 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. Progress: Although some folks would like to see large-scale trials, the small-plot on-farm design worked amazingly well with our audiences because the results, if there are differences, are very visible. Talks were given on conducting on-farm research at each of the extension meetings and photos of S deficiencies at the Aurora Research Farm were shared and used for discussion with audiences.

Milestone: (4) 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 K management at home, in year 4 of the project. Progress: We collected data from 43 fields in addition to the research trials that were conducted at three locations in the state, in collaboration with growers, extension and consultants. Talks were requested by extension and consultant and industry to share the results with their clients. About 80 people attended the Field Crop Dealer Meeting, in addition to about 60 who attended the Helena winter meeting and about 35 who were at the Valatie Research Farm field day. Public press articles including a farmer impact story (western NY farm) are being written in the coming winter months.

Impacts and Contributions/Outcomes

There is a growing awareness of the need to survey fields for S deficiencies. The S deposition maps of the National Atmospheric Deposition Program (http://nadp.sws.uiuc.edu/data/animaps.aspx) show the great improvements in air quality have resulted in a considerable reduction of S deposition, with average levels now less than 9 lbs S/acre. Typical crop removal values for alfalfa average about 5 lbs S per ton of dry matter, for a state average removal rate of about 16 lbs S per acre, greatly exceeding the average deposition rate. Farmers and farm advisors who attended our summer and winter training sessions (about 80 people attended the Field Crop Dealer Meetings this year), were trained to recognize deficiencies, and a new tool for S management was introduced: the Cornell soil S test. Our research has shown this new test to be effective in identifying fields with the potential for an S deficiency. The same extraction can be used to determine the soil’s cation exchange capacity and potassium, calcium and magnesium saturation ratios. Discussions are ongoing with commercial laboratories to implement the test package (S, CEC and saturation ratios) and make it available to farmers.

There is also great interest in knowing how to manage for K and that is the reason why we evaluated the new soil test for its ability to accurately predict the soil’s cation exchange capacity, and K saturation ratio. Our guidelines for K management are based on the Cornell Morgan test and field trials have shown this to be the best predictor of a potential for a K deficiency. The new test allows us to also evaluate the use of K saturation ratio for managing K. Results to date show that both soil test data are directionally correlated but that the risk of over- or under-application of K with use of a K saturation threshold can be high (depending on the cutoff %K used).

As mentioned before, our biggest pride has been the growing number of people that are now engaged in on-farm research, illustrating a growing willingness among farm advisors and farmers to be a partner in the on-farm research. This is the way to move forward, gaining buy-in and a critical mass for research at the same time. It greatly speeds up the implementation process. We initiated the NY ON-Farm Research Partnership several years ago, and continue to develop working relationships among the many collaborators while also trained them in on-farm research for impact beyond this project.


Dr. Jerry Cherney

Cornell University
503 Bradfield Hall
Crop and Soil Sciences Department
Ithaca, NY 14853
Office Phone: 6072550945
Website: http://www.forages.org
Karl Czymmek

Senior Extension Associate
PRODAIRY, Cornell University
328 Morrison Hall
Animal Science Department
Ithaca, NY 14853
Office Phone: 6072554890
Website: http://nmsp.cals.cornell.edu