Este trabalho teve como objetivo analisar o efeito do número de operações mecanizadas de nivelamento da superfície do solo sobre os componentes de rendimento e altura da lâmina de água na cultura do arroz irrigado. O estudo foi realizado em uma área subdividida em dois talhões de 15 hectares, sendo conduzida sob sistema de cultivo mínimo. As variações no número de operações de nivelamento do solo, constituíram de uma e duas operações, utilizando um conjunto mecanizado composto de trator e plaina niveladora hidráulica. Foi utilizado um grid com intensidade amostral de um hectare, sendo analisados a altura média da lâmina de água e os seguintes componentes de rendimento: população de plantas, número de panículas, produtividade e grãos inteiros (rendimento de indústria). A produtividade de arroz e a altura média da lâmina de água não foram influenciadas pelo número de operações mecanizadas de nivelamento do solo. A maior correlação observada referente à produtividade foi o número de panículas por área, mas sem interferência significativa no rendimento final da cultura. Também, pode-se observar baixa correlação entre rendimento de indústria e produtividade, em ambos os tratamentos. Portanto, a realização de uma segunda operação de nivelamento do solo, nas condições em que o experimento foi realizado, não se justifica economicamente, pois o incremento de produção não cobre os custos da segunda operação.
This study determined the spatial variability of soil penetration resistance and yield of the soybean crop in lowland areas. The soil resistance to penetration at four different depths (0 to 0.10 m; 0.11 to 0.20 m; 0.21 to 0.30 m and 0.31 to 0.40 m), volumetric humidity of the soil at two depths (0 to 0.20 m and 0.21 to 0.40 m) and soybean yield were determined in an area of 1.13 hectares, using a sample mesh of 10 x 10 m. The corresponding data were subjected to descriptive statistical analysis. Pearson’s simple linear correlation analysis (p≤0.05) was conducted and the spatial dependence was assessed by analyzing the isotropic semivariograms using spherical, exponential, linear, and Gaussian models. The results showed that the soil penetration resistance increased with depth, with restrictive values to root growth between 0.05 and 0.35 m. There was no correlation between yield and soil penetration resistance, and the semivariograms did not show a defined ascending region regarding the soil penetration resistance data. For the conditions under which the experiment was conducted, the sample 10 x 10 m mesh was suitable for assessing the spatial variability of soil resistance to penetration in depths exceeding 0.10 m.
The objective of this work was to determine the optimal plot size and the number of replicates for the evaluation of the fresh weight of ryegrass sowed in rows. Seventy uniformity trials were performed with 'Barjumbo' ryegrass, in 16 basic experimental units (BEUs) of 0.51 m2 each. The fresh weight of ryegrass in the BEUs of 18, 18, 6, 6, and 22 uniformity trials was determined, respectively, at 130, 131, 133, 134, and 137 days after sowing. The optimal plot size was determined through the method of the maximum curvature of the coefficient of variation. The number of replicates was determined in scenarios formed by combinations of treatments and differences between means to be detected as significant by Tukey’s test, at 5% probabilit y. The optimal plot size ranged from 1.73 to 3.18 m2, and the variation coefficient in the optimal plot size from 7.58 to 13.96%. The number of replicates varied from 3.95 (~4) to 32.27 (~33), depending on the experimental design, the number of treatments, and the adopted minimum difference. The optimal plot size is 2.29 m2, and, in experiments with up to 50 treatments, eight replicates are required to identify as significant the differences between treatment means of 20.24%.
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