EVALUACION DEL DISCO PARA ESTIMAR LA DISPONIBILIDAD EN UN PASTIZAL DE Neonotonia wightii

Abstract

Double sampling technique was evaluated using a 0,25 m² disk in a Neonotonia wightii sward under grazing conditions.  Eighty pairs  of  observations  of  height and weight of  reference quadrats  (0,25 m²) were taken and grouped in such a way that they were increased 5 times from 5 up to 80. A lineal relation was established among plant height and the yield of each quadrat. Regression analysis was applied using the minimal quadratic method. Standard residual deviation (SRD) and variation coefficient (VC) associated to the regression were the criteria utilized to establish the technique precision. Yields were found to be satisfactory with the disk and cutting. Most of VC values did not exceed 9% and the standard error of the regression did not surpass 32 kg of DM/ha; besides, differences among regression coefficients were not found. Disk estimation error and that of the cutting were corrected by the increment of reference quadrats (n); a similar behaviour was found in r and SRD values. It is concluded that disk technique may be used to predict glycine availability using samples from 5 to 20 pairs of observations in order to calculate the regression line.