Optimal quadrat area and sample size to estimate the forage mass of stargrass

Abstract

The objective of this study was to evaluate the sample size and area of the quadrats necessary to accurately estimate the forage mass (FM) of a fenced pasture of stargrass (Cynodon nlemfuensis cv. Florico) during the winter. Five metal quadrats were used: a 0.09 m² square (0.30 m side), a 0.25 m 2 square (0.50 m side), a 0.25 m 2 circle (0.28 m diameter), a 0.5 m 2 rectangle (0.5 x 1.0 m), and a 1 m 2 square (1.0 m side), each with eight replicates. The size and shape of the quadrats were determined based on cumulative variances to identify combinations that minimized the coefficient of variation (CV). The minimum sample size required to estimate the FM, morphological components and height was established by the CV maximum curvature method. The 0.25 m 2 square quadrat (0.5 m side) presented the lowest cumulative CV in estimating the FM and the dry mass of dead material. However, for the estimation of the leaf and stem dry mass, the 1.00 m 2 square quadrat (1.00 m side) presented the lowest CV. Using the 0.25 m 2 square quadrat, a minimum number of six samples were required for the FM estimation, and eight samples were required for estimating the mean height of the stargrass pasture. Therefore, at least eight samples are recommended to obtain accurate results for the estimation of both variables. Key words: Cumulative coefficient of variation. Cynodon nlemfuensis. Height. Morphological composition. ResumoO objetivo desse estudo foi avaliar o tamanho e a área da moldura necessários para estimar a massa de forragem (MF) de um pasto vedado de capim-estrela (Cynodon nlenfluensis cv. Florico) durante o inverno. Foram utilizadas cinco molduras metálicas: quadrado de 0,09 m² (0,30 m de lado), quadrado de 0,25 m² (0,50 m de lado), circular de 0,25 m² (0,28 m de raio), retangular de 0,5 m² (0,5 x 1,0 m) e quadrado de 1 m² (1,0 m de lado), cada uma com oito repetições. A dimensão e o formato da moldura foram determinados com base nas variâncias acumuladas para escolha da combinação com menor coeficiente de variação (CV). O número mínimo de amostras necessárias para estimativa da MF, dos componentes morfológicos e da altura foi estabelecido pelo método da máxima curvatura do CV. A moldura de formato quadrado e 0,25 m 2 de área (0,5 m de lado) apresentou menor CV acumulado

Optimum sampling size for straw and grain yields and plant height in experimental plots of wheat

“…Accordingly, accurate and reliable evaluation of crop straw yield is a prerequisite for optimizing straw retention in the soil and its removal from the field. Variation in data could be attributed to controllable variables, such as selection of a representative sampling area (Taye et al, 2000;Knörzer et al, 2013;Zanella et al, 2017).…”