This article explores the response of three genotypes of Amaranthus to different sowing date and to different doses of nitrogen (N) fertilization. The experimental design was a randomized complete block design with three replicates for cultivars, planting date and fertilization per treatment. Mexicano sown in early December had the best yield (5285 kg ha -1 ) with highly significant differences (p < 0.001) respect to Dorado and Antorcha. To assess the N fertilization Mexicano cultivar was sown at the end of spring (1 December). Morphophysiological variables increased as the N fertilization dose was raised. Higher doses of N fertilizer resulted in greater economic yields this was mainly due to the increase in grain number rather than that of a 1000 grain weight. The results of this investigation suggest that sowing Amaranthus cruentus cv Mexicano on 1 December with 150 kg N ha À1 favors its general development and allows to obtain high economic and biological yields with an appropriate protein content.
In Argentina there have been few evaluations of Andean pseudocereal plantings. This study explored the response of Amaranthus cruentus cv Mexicano to different plant densities under furrow irrigation in the lower valley of the river Negro, Patagonia, Argentina. The experimental design consisted of 3 blocks with randomized treatments (subplots), each one corresponding to different plant density. The treatments were sown in rows with spacing of 0.70 m (one row per ridge) and others with a spacing of 0.35 m (two rows per ridge). The plant densities evaluated were: 70,800-84,200-97,700-116,000-114,000-225,300 and 394,000 plants ha-1. Different biometric variables and their components were measured: plant height, number of leaves, biomass and economic yield. The results suggest that the optimum plant density was 116,000 plants ha-1 with a row spacing of 0.70 m. This density produces an adequate plant stand from which to harvest optimal biological and economical yields. The contributions of this study demonstrated the potential of the A. cruentus crop in the lower valley of the river Negro, representing the southernmost study of plant density made for this pseudocereal in the world.
Understanding the mechanisms that drive population dynamics is fundamental for management of wild populations. The guanaco (Lama guanicoe) is one of two wild camelid species in South America. We evaluated the effects of density dependence and weather variables on population regulation based on a time series of 36 years of population sampling of guanacos in Tierra del Fuego, Chile. The population density varied between 2.7 and 30.7 guanaco/km2, with an apparent monotonic growth during the first 25 years; however, in the last 10 years the population has shown large fluctuations, suggesting that it might have reached its carrying capacity. We used a Bayesian state-space framework and model selection to determine the effect of density and environmental variables on guanaco population dynamics. Our results show that the population is under density dependent regulation and that it is currently fluctuating around an average carrying capacity of 45,000 guanacos. We also found a significant positive effect of previous winter temperature while sheep density has a strong negative effect on the guanaco population growth. We conclude that there are significant density dependent processes and that climate as well as competition with domestic species have important effects determining the population size of guanacos, with important implications for management and conservation.
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