Lâminas de irrigação versus coberturas do solo e adubação borácica na cultura do girassol sob as condições edafoclimáticas de Russas - Ceará

Abstract

The use of sunflower in grain and biodiesel production, makes it potentially important in Brazilian projects of social inclusion. However, to optimize the production of those oilseeds, it is necessary to gather information on certain practices, such as: the association be tween forms of irrigation and soil mulch and the proper fertilization, taking into account the sensitivity of the culture to boron deficiency . That said, this study was aimed at evaluating the effect of the interaction between irrigation and soil mulch cover types, and the effect of boracic fertilization in sunflower cultivation. The work consisted of two experiments, implanted in a randomized complete block design. The experiment 01 was conducted in the split plots scheme consisting of five irrigation dept hs (25, 50, 75, 100 and 125% of class “A” pan evaporation) in the plot and four types of soil mulch (straw rice; carnauba straw, wood shaving and without cover) as subplots with three replications. The experiment 02, also in blocks, consisted of five treat ments and five repetitions with the application of 1, 2, 3, 4 and 5 kg. ha-1 of boron in the conventional manner. All the required cultivation (and phytosanitary) practices were carried. The evaluated variables were: plant height, stem diameter, weight of 1000 seeds, average weight of achenes, achene yield potential, oil content of grain and oil yield potential. The data from the evaluated variables was subjected to analysis of variance by F test, and when significant effects were detected, the effects of qualitative nature were compared using Tukey's test and those of quantitative nature were submitted to regression analysis. In experiment 01, all variables showed statistical inference in the face of irrigation depths, except the oil content. In the same exp eriment, the water depth 807.1 mm (125% CAE) gave a maximum yield of 1634.25 kg ha -1. The potential for oil yield in kg ha -1was significantly affected by irrigation water applied with a maximum of 675.88 kg.ha-1 oil (125% CAE). The average oil content of the seeds was found to be 41.38%. The different soil mulches and the interaction between irrigation depths and soil mulches caused no significant effect on the evaluated variables in experiment 02. On the other hand, the plant height and stem diameter weresignificantly influenced by the levels of boron and by the time of data collection, but not by the interaction rates of boron amount versus collection time. The dose of 4 kg,ha-1 of boron maximized the average mass of seeds (48.95 g), the potential productivity of seeds (2442.34 kg ha-1) and potential oil yield (1076.58 kg ha-1). The average oil content of seeds was found to be 43.49%.