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2004
Standing Crop Quality of Alfalfa Prediction Model
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Maps of Relative Feed Value in Alfalfa for Manitoba:
This model is designed to predict the standing crop quality of pure
alfalfa stands at the first cut timing across
Manitoba.
A strong correlation has been observed between the accumulation of
growing degree-days and the development of alfalfa. The developmental
stage of alfalfa has previously been shown to be a good indicator of
standing crop quality of alfalfa (PEAQ - Predictive Equations for
Alfalfa Quality). It is being released as a product under development to
be used in conjunction with other predictive tools to evaluate the
standing crop quality of pure alfalfa stands for the purposes of timing
forage harvest.
Background
The
model has been developed for use on pure alfalfa stands with 35 or more
stems per square foot that are in their second to fifth year of
production. Use of the model on older stands that have less than 35 stems per
square foot may lead to inaccurate
prediction of standing crop quality. Use of the model to predict
standing crop quality of stands with a grass component will result in
increasingly inaccurate prediction with increasing percentage of grass
in the stand.
Use of the Model to Predict Opportune Cutting of the First Cut
Cutting alfalfa to meet market specifications can affect yield and
animal nutrition. For this reason, it is beneficial to target a
specific Relative Feed Value (RFV) target when harvesting alfalfa. After selecting an RFV
target based on the intended market or class of livestock to which the
forage will be fed, the prediction model can be used to select the
optimum timing of forage cutting.
Figure 1. Nutritional requirements of beef and dairy cattle as measured
by the Relative Feed Value (RFV) Index at differing stages and times in
the production cycle.
As
a general rule of thumb, alfalfa should be cut when it reaches a
standing crop RFV 20 points higher than the RFV target. The 20 point
rule allows for the increase in fiber content that is generally observed
between cutting and baling/chopping.
Accuracy of the model
As
with any biological science involving the prediction of crop quality
parameters, there is a margin of error that can be expected. Indications
are that the growing degree day model for the prediction of standing
crop quality will predict the standing crop quality of pure alfalfa
stands within plus or minus 15 RFV points 95 times in 100. For producers
who have precise RFV targets, it is recommended that alternative methods
of measuring standing crop quality (scissor clipped NIR or wet chem
analysis and PEAQ) be used in addition to the RFV model.
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