Abstract
Sunn hemp (Crotalaria juncea L.) is an annual cycle legume with high potential for biological nitrogen fixation, being widely used in crop rotation for biomass formation and control of nematodes. The objectives of this study were to determine the sample size for the mean estimation of productive traits of sunn hemp and verify the sample size variability between traits and sowing dates. Two uniformity trials were performed in the agricultural year 2014/2015, with sowing in October (trial 1) and December (trial 2). At the crop flowering stage, 300 plants of each trial were harvested and fresh and dry matter of leaves, stem, root, aerial part, and total weight were evaluated. The normality and randomness tests were performed for each trait and the sample size was calculated for the semi-amplitudes of the confidence interval (estimation errors) of 2, 4, 6, 8, 10, 12, 14, 16, 18 and 20% of the mean estimate. There is sample size variability between productive traits and between sowing dates. The assessment of at least 101 plants is required for mean estimation of productive traits with maximum estimation error of 20% of the mean and 95% confidence level.
Highlights
Sunn hemp (Crotalaria juncea L.) is a native species from India, with wide adaptation to tropical regions. This legume is a shrub, standing upright 2 to 3 meters high and with deep root system, which assists in soil decompression and nutrient recycling. This species is used in crop rotation and stands out among the soil cover crops due to the P and Mg accumulation, high biomass production, reaching up to 16.5 t ha-1 of dry matter and nitrogen fixation up to 298 kg ha-1 of N (Mangaravite, Passos, Andrade, Burak, & Mendonça, 2014; Silva et al, 2014; Xavier, Oliveira, & Silva, 2017)
Two uniformity trials with sunn hemp (Crotalaria juncea L.) distributed in two sowing dates were performed in the experimental area from the Department of Plant Science of the Federal University of Santa Maria, Santa Maria, Rio Grande do Sul state in the agricultural year 2014/2015
For fresh matter of roots, the sample size is 51 and 83 plants respectively for the first and second sowing dates. These results demonstrate the necessity of using different sample sizes for mean estimation of productive traits
Summary
Sunn hemp (Crotalaria juncea L.) is a native species from India, with wide adaptation to tropical regions. This legume is a shrub, standing upright 2 to 3 meters high and with deep root system, which assists in soil decompression and nutrient recycling. Factors such as availability of time, labor, financial and human resources generally limit the evaluation of all plants of the entire experimental unit (plot). Commonly only part of the plot is evaluated, i.e., only a few plants (sample) in order to minimize the limiting factors. The sample should be representative of the plants of the experimental unit (Storck, Garcia, Lopes, & Estefanel, 2016)
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