Brian Lang, Crops Field Specialist, Northeast
For the last decade, there has been a slow progression of the number of alfalfa fields across northeast Iowa exhibiting a light green to dark green mottled coloration. Farmers expressed concern about poor alfalfa production in the light green areas. Plant disease analysis and soil tests were not able to explain the majority of these situations.
ISU Extension Crops Specialist initiated preliminary investigations in 2004 and expanded the work into a series of research trials in 2005.
The preliminary investigation in 2004 found that the mottled colorations coincided with different soil organic matter levels in the fields. The lighter green alfalfa lacked normal nodule development for nitrogen fixation. These factors suggested a sulfur deficiency problem. Sulfur fertilization has always been recommended for alfalfa grown on sandy, low organic matter soils, however the fields in question exhibiting these symptoms were finer textured, higher organic matter loam and silt loam soils.
Potential contributing factors to a developing wide-spread sulfur deficiency problem in northeast Iowa includes: (1) Atmospheric sulfur deposition has decreased by over 500% in the last 30 years. Current sulfur deposition is only 3 pounds per acre www.epa.gov/air/airtrends/aqtrnd98/chapter7.pdf . Alfalfa removes approximately 25 pounds of sulfur per acre per year. (2) The sulfur soil test is not accurate at predicting sulfur needs for crops, however, many farmers and fertilizer dealers are unaware of this. (3) Plant analysis is the preferred method for determining the need for sulfur, but it is not convenient or well understood.
On-farm research plots were established in 2005 with 5 farmer cooperators. Plant and soil samples were collected for disease analyses, nutrient analyses, and soil tests. Sulfur fertilizer treatments were applied and alfalfa yield responses measured.
The on-farm demonstrations found 2 significant problems. One was a fairly high prevalence of Aphanomyces root rot. The other was a highly significant response to sulfur fertilizer. The 5 research plots showed an average net profit of $50 per acre with sulfur fertilizer treatments.
The research data was presented to approximately 2,400 alfalfa growers and agricultural providers during ISU Extension meetings from November 2004 through April 2006. Approximately 75% of the audience saw similar visual symptoms on their farms, while many others were uncertain and would evaluate their situation next season.
Because of this ISU Extension effort, many farmers tried sulfur fertilizer applications in 2005, and/or will try sulfur applications in 2006. Those that used sulfur in 2005 commented about the remarkable response of at least doubling their alfalfa yields on these lighter green areas. Based on the number of positive responses and number of acres of alfalfa being treated, it is estimated that proper adoption of sulfur fertilizer management will provided an overall net profit of about $5 million dollars to alfalfa producers in northeast Iowa within 2 years.
April 27, 2006
103 - Nutrient Management
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July 8, 2006
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