Plano amostral em parcelas de milho para avaliação de atributos de espigas

Abstract

Em experimentos agrícolas, a amostragem é importante para reduzir os custos e a mão-de-obra, embora devam possuir características que confiram precisão experimental adequada. O objetivo do trabalho foi determinar uma metodologia para se amostrar parcelas e sub-parcelas experimentais de milho, quando o objetivo é avaliar atributos morfológicos e de rendimento avaliados nas espigas. O experimento foi realizado, no Departamento de Fitotecnia da Universidade Federal de Santa Maria, com quatro bases genéticas de milho (híbrido simples - DAS 9560; híbrido duplo - AG 303; híbrido triplo - AG 6018; variedade cultivada - BR 202). O delineamento usado foi blocos completos casualizados com quatro repetições. A parcela foi constituída de 96 sub-parcelas de um metro. Em cada parcela, amostraram-se as espigas de cinco sub-parcelas. Foram avaliados o comprimento, o diâmetro, o rendimento de grãos e a massa de cem grãos de cada espiga. Concluiu-se que o tamanho da amostra nas parcelas de milho está relacionado ao atributo a ser avaliado nas espigas. Existem interferências genéticas e ambientais sobre a magnitude da estimativa do tamanho da amostra de espigas de milho. Pode-se amostrar 24 espigas por parcela, em seis repetições por genótipo, para avaliar os atributos comprimento e largura de espigas, rendimento de grãos e massa de cem grãos, para obter uma semi-amplitude do intervalo de confiança abaixo de 10% da média.

Sample size for single, double and thee-way hybrid corn ear traits

“…In such cases, the use of a greater number of replications due to a smaller number of corn ears per experimental unit (by keeping the total number of corn ears per hybrid) is more efficient for the reduction of the estimated average variance for a certain hybrid (Barbin, 2003). As a result, it is possible to redesign the experimental design to a greater number of replications (Martin et al, 2005b).…”

“…weight, grain weight, cob weight and weight of 100 grains, the effect of the hybrid was not significant, probably due to the significance of the experimental error, increased by block × hybrid interaction (Table 2). In these cases, differences in ear traits among hybrids depend on the block (environment), which makes the sample size dependent on the genotype (Martin et al, 2005b). For the variables of which the experimental error effect was significant, the estimated sample size (Table 3) was much greater (average of 21 ears, for D5) than for the other six traits with hybrids with significant differences (average of 10 ears, for D5).…”

“…, following the study of Martin et al (2005b), where CV is the coefficient of variation of the sampling error (in percentage), D is the half-amplitude of the confidence interval (in percentage) for the average (it was established that D=5% and D=10%) and t is the critical value of the t distribution, at a 5% (two sides) level of error probability. The size of estimated samples refers to the estimate, at 5% precision (D5) or 10% (D10) of the estimated mean, in the experimental unit.…”

“…Although sampling number is an alternative, it is necessary to know beforehand the population variance and the desired accuracy degree for each trait to be assessed, as well as possible genetic interferences (Martin et al, 2005a;2005b) when creating a single random sampling.…”

“…Apart from these authors, Silva et al (1998), using simple sampling, concluded that 11 ears are required per plot to estimate the number of grains per ear, cob length and weight. Martin et al (2005b), using simple sampling, concluded that 24 ears per plot are required in six replications per genotype, thus obtaining the semi-amplitude of the confidence intervals bellow 10% of the average, to assess the ear length and diameter, yield of grains and weight of 100 grains. Also, the simple sampling of ears in plots with the same number of plants distributed in two or three rows provided more experimental accuracy than when distributed in a single row (Palomino et al, 2000).…”