Looking Back on Seven Years
  of Alfalfa Scissor-cutting

Another unique year for alfalfa scissor cutting. May was extremely cool and alfalfa development was slow. Finally, out of sheer principle, we started sampling on May 27. Not to anyone's surprise, relative feed values (RFV) were more similar to Ken Griffey Jr.'s batting average than forage that was nearly ready to harvest. Like 1996, it was early-June weather that dictated when producers could harvest rather than choice based on forage quality. About 150 calls were logged on the forage quality FREELINE.

This was the third consecutive year where NIR, PEAQ, and wet chemistry were compared to each other for estimating forage quality. Several conclusions can be drawn from these comparisons. First, the NIR analysis tends to indicate a higher acid detergent fiber (ADF) value than wet chemistry. The 1997 comparison is shown in Figure 1. In thirty comparisons from 1995 through 1997, ADF values were higher for NIR versus wet chemistry ninety percent of the time. Comparing PEAQ estimates of ADF to that of wet chemistry, values were higher for 12 sample dates and lower for 18 comparisons. The average difference between the PEAQ and wet chemistry analyses was only 0.4 percentage units.
 

 

The trend for neutral detergent fiber (NDF) is opposite that of ADF. That is, about 60% of the time (18 of 30 comparisons) NDF was underestimated by NIR compared to wet chemistry. This trend was weakest in 1997 compared to 1995 and 1996. In those two years, NDF was underestimated compared to wet chemistry in 16 of 20 comparisons or 80% of the time. For PEAQ, there was about a 50% split in terms of being over or under the wet chemistry value for the three years. Because NIR is overestimating ADF and underestimating NDF in many site-year comparisons, we find that RFV estimates are reasonably close to each other. Average RFV's for 1997 are presented in Figure 2. Overall, PEAQ has proved to be a reasonably good estimate of forage quality.
 
 

 
 

Finally, as we look back over our seven years of alfalfa scissor-cutting, the trend is clear toward progressively later optimum first-cut harvest dates from 1991 to 1997 (Figure 3). In 1991 (our first year), RFV on May 20 was 174. This compares to an estimated RFV on the same date during this year of 278. If this trend continues (and hopefully it won't), by year 2000 we'll be making first cutting July 4 for optimum quality. This trend does not present a strong case for global warming. One fact remains clear, don't base first cut harvest date on either stage of maturity or calendar date. It's a sure strategy for a forage quality train wreck.

 
 
For more information contact Mike Rankin
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