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.
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.