Relación entre materia seca presente y altura en gramas nativas del trópico mexicano

Abstract

Standing dry matter (SDM, kg ha-1) measurements should be quick and precise, something difficult to achieve using traditional direct cutting methods, but possible to do so when, through double sampling, this traditional method is combined with quick indirect measurements of variables correlated to SDM, such as pasture height (PHT, cm). The objective of the present study was to: 1) estimate the relationship between PHT and SDM, 2) estimate the minimum number of PHT readings (n') necessary to estimate an average, and 3) develop an empirical model, to derive n' from published coefficient of variation values (CV). SDM and PHT were related by simple linear regression through the origin in three studies (S1, 3/III-15/VI, 1995, S2, 18/VII/ 98-30/I/99, S3, 18/VIII-12/II, 2003). Slopes went from 183 to 303 kg SDM cm-1 PHT, coefficients of determination (R2) ranged from 0.83 to 0.96 and residual standard deviations (RSD) between +-341 and +-1895. In S3, n' values were 61 and 103 before and after grazing, respectively. The third degree polynomial: n'= 0.21-0.014(CV)+0.039(CV2)-0.00000209(CV3), n=45, R2= 1.00, RSD= +-0.0096, presented the best fit. It was concluded that SDM can be reliably predicted from PHT, before grazing n' values should be lower than after grazing, the use of a third degree polynomial to estimate n' from published CV values is suggested, and also, that it is necessary to study the relationship between SDM and PHT in other pastures under different management conditions.