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Introduction (Grass, Alfalfa-grass, Alfalfa)

It is particularly difficult to assess standing quality of pure grass without actually analyzing samples. Grass morphology changes are not obvious until heading, once grass has headed it is too late. Often a calendar date works as well as any morphological indicators for spring harvest. In our region this date varies from May 15 to May 30.

A study was undertaken recently to develop a system for estimating standing NDF of alfalfa-grass mixtures (Parsons, 2005). Figure 3 shows the estimated optimum NDF of standing forage at harvest for mixtures and pure alfalfa or pure grass. These goals assume a 10-15% decline in forage quality due to harvest, storage and feedout.

Figure 3.     Optimum NDF of standing forage, assuming pure stand optimums of 38% for pure alfalfa and 50% for pure grass.

Figure 4 is the estimated alfalfa height needed to harvest at optimum stand NDF. For a more accurate estimate of standing NDF in mixtures, we have equations based on alfalfa height, sampling date, and an estimate of the grass:legume ratio (10-30%, 30-50%, etc.). Prediction equations for NDF of mixed alfalfa-grass stands were developed based on sampling and separating mixtures from fields across NYS in 2004 and 2005. Table 1 is based on a prediction equation using alfalfa height and percent grass.

Figure 4.   This provides a gross estimate of alfalfa height (height of tallest stem) at harvest, for pure stands and mixtures. For mixtures, use alfalfa height in the mixture. For 100% grass, use estimated height in a pure stand of alfalfa nearby.

Table 1.    Estimated stand NDF of a mixed alfalfa-grass stand based on alfalfa height and the percent grass in the stand. Target NDF for each mixture is highlighted.