THE WEIBULL DISTRIBUTION TO DESCRIBE ABOVEGROUND BIOMASS OF Lolium multiflorum LAM., IN RELATION TO RATE OF NITROGEN APPLICATION

Abstract

Characterization of forage biomass in pasture land is complicated by the temporal and spatial variability that result from variation in vegetation patch sizes. These factors along with topography, water location and distribution of fertilizer result in non-uniform grass. The aim of the study was to evaluate the use of the three-parameter Weibull distribution to describe aerial dry matter (DM) production in the first harvest of a mixture of three Italian ryegrass (Lolium multiflorum Lam.) cultivars (the tetraploid ‘Jivet’ and ‘Barspirit’, and the diploid ’Barprisma’) in Asturias (N Spain). The trial was established in a randomized complete block design with three blocks of 100 m2 (20 m x 5 m) and a fertilizer treatment with three levels (0, 40 and 80 kg N ha-1) assigned at random to each block. In 2010, 2011 and 2012, samples of vegetation (28-30) were collected at random from each treatment plot to enable modelling of aerial DM production. The null hypothesis that the distributions studied follow a Weibull distribution was tested. The three-parameter Weibull distribution was fitted by the method of Moments, and the goodness of fit was tested with the KolmogorovSmirnov test (a=0.05). The Weibull distribution function proved to be a flexible and simple model that enabled description of 100 % of the distributions.