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ABSTRACT:This work aimed to analyze possible differences in growth patterns on Eucalyptus species and to identify the determinants climatic variables on the growth. We evaluated six Eucalyptus species (Eucalyptus camaldulensis, Eucalyptus grandis, Eucalyptus urophylla, Eucalyptus saligna, Corymbia citriodora and Eucalyptus globulus) and a Clone (GG100) implanted in an experimental arrangement of randomized blocks. We collected the collar diameter and height of all plants monthly in the course of a year, in addition to climate data (minimum temperature, maximum and rainfall). Sequentially, we obtained the correlations between the current monthly increments (collar diameter and height) and climatic variables (minimum temperature, maximum and rainfall). The Current Monthly Increment of the Collar diameter (CMI D) was not correlated to the climatic variables evaluated and the Current Monthly Increment of the Height (CMI H) was strongly correlated to the minimum temperature for the species E. camaldulensis, C. citriodora, E. saligna, E. urophylla, E. grandis and the GG100 Clone. The Rainfall showed positive correlations regarding the CMI H only for the Clone (GG100) and E. urophylla. Finally, the species E. camaldulensis, E. urophylla, E. grandis, E. saligna presented a mortality rate under 10% which is recommended according to the silvicultural criteria.

Highlights: How many times a day should we irrigate eucalyptus seedlings in less technified nurseries? Twice the ETo was the amount of water used for the irrigation of the eucalyptus seedlings. It takes 295 litres of water to produce 1 kg of dry eucalyptus biomass. Two daily irrigations are sufficient for the production of eucalyptus seedlings. The substrate with 80% vermiculite should be used for the production of eucalyptus seedlings.

One of the bottlenecks in relation to the production of forest seedlings is irrigation, especially in less-tech nurseries. The small volumes of substrate, where the seedlings develop, lead to low water storage. This fact can lead to water deficit and significant losses in the production of seedlings, generating even mortality. The objective of this study was to determine the best irrigation frequencies for Eucalyptus grandis seedling production in less-tech nurseries. The experiment was conducted between 2013/08/04 and 2013/23/07 (106 days) and conducted in Chapadão do Sul county, Brazil. The experiment was set up in a randomized complete block design, with five replications. Four irrigation frequencies were tested: IF1 (one daily irrigation - 11:00 a.m.), IF2 (two daily irrigations - 11:00 a.m. and 7:00 p.m.), IF3 (three daily irrigations - 07:00 a.m., 11:00 a.m. and 7:00 p.m.) and IF4 (four daily irrigations - 07:00 a.m., 11:00 a.m., 3:00 p.m. and 7:00 p.m.). The sample units were composed of eight seedlings in 50 cm3 conical tubes filled with soil and vermiculite in a volume ratio of 1:1. The irrigation depth was estimated by reference evapotranspiration (Penman-Monteith) multiplied by a crop coefficient equal to two. Plant height, number of definitive leaves, shoot dry mass (root and total), seed quality index, survival and efficiency of water use by eucalyptus seedlings were evaluated. The average daily irrigation depth in the experimental period was 5.2 mm. Based on the results, it is recommended for eucalyptus seedling producers, in less-tech nursery, irrigation management twice per days. (11:00 a.m. and 7:00 p.m.).