Predicting Alfalfa Stand Nutritive Value by An Indirect Method In Southern U.S.A., and North of Mexico.

Predictive equations for alfalfa quality (PEAQ) have demonstrated accuracy to predict NDF and ADF concentrations in northern USA and Canada, but information is lacking about how PEAQ will perform in lower latitudes. The objectives of this study were 1) to determine if PEAQ can be validated for New Mexico, USA, and North of Mexico and 2) to determine if PEAQ calibration has to be specific for each of these two regions. Alfalfa fields near Artesia and Las Cruces, New Mexico, and in  the valley of Mexicali, B.C., Mexico were sampled in 2010 from April to October. Alfalfa sampling was initiated when it reached 30 cm height and continued until alfalfa was 30% bloom for each growing cycle. Samples from a 0.25 m² area were taken every week, five samples per week. The longest stem (MAXHT) and maturity stage of the most mature stem (vegetative, bud, or flower) (MAXSTAGE) were recorded. Samples were oven dried at 60^○C, for a minimum of 48 h, ground to pass a 1-mm screen and analyzed  for NDF and ADF concentrations. All alfalfa samples were analyzed in the same laboratory. A multiple regression analysis was run with MAXHT and MAXSTAGE against NDF or ADF and the resulting equations were compared with the corresponding original equations. Similar regression coefficients and r² were found for both New Mexico and Baja California, with r²= 0.82 and r² = 0.73 for ADF and r²= 0.77 and r² = 0.71 for NDF, respectively. The equations from the three fields combined were similar to those of the original PEAQ, with r²= 0.79 and r² = 0.73 for ADF and NDF, respectively. It is concluded that PEAQ can be used to predict alfalfa nutritive value in New Mexico and the valley of Mexicali, Baja California, Mexico.