See more from this Session: Crop Responses, New Management Strategies, and Improved Methods for Assessing Sulfur Needs I
Wednesday, October 19, 2011
Henry Gonzalez Convention Center, Hall C, Street Level
Alfalfa is an important forage crop in New York State (NY). Over the past decades, atmospheric S deposition has decreased, raising questions about the S status of alfalfa. On-farm S response trials were conducted in eight locations in NY, comparing two S sources (CaSO4 and K2SO4.MgSO4 at 134 kg S/ha applied after 1st cutting in 2008) versus a no-S control in four replications. Forage quality and yield were monitored for two years following the application. Soil samples (0-15 cm depth) were taken prior to applying treatments in 2008 and in early spring in 2009. Tissue samples (top 15 cm) taken at 3rd cutting were analyzed for total S. In 2008, four sites with <2.5 mg/kg tissue S were responsive to S addition while three sites with tissue S levels >2.5 mg/kg were non-responsive. One site had a tissue S level <2.5 mg/kg but was non-responsive to additional S, most likely due to the low pH of the site. Sulfur addition increased tissue S in both years. In 2009 only one site had significantly higher total yield where S has been applied, and all sites showed tissue S levels that had dropped below 2.5 mg/kg in both the treated and untreated plots. Milk per ton estimates were not impacted by S addition. Soil test results showed that soils with CaCl2 extractable S of 8 mg/kg or less might benefit from S addition. We conclude: (1) there is a potential for a yield response upon S addition to alfalfa in NY, (2) tissue testing is effective in identifying S deficient sites (<2.5 mg/kg S) for sites that are otherwise managed optimally (correct pH), and (3) a soil test of <8 mg/kg indicates the probability of a response to S addition.