Influência da adubação nitrogenada aplicada em diferentes épocas na qualidade fisiológica de sementes de sorgo granífero (Sorghum bicolor (L.) Moench)

Abstract

This research was developed on the Experimental Farm of the Curu Valley, in Pentecoste, Ceará, and in the Seed Technology Laboratory of the Federal University of Ceará, Brazil. The objective of this study was to compare the effect of nitrogen fertilization (ureia-45%) applied at 60kg N/ha in complete and fractional doses, during the development of the grain sorghum (Sorghum bicolor (L.) Moench), cultivar EA-955. Seven treatments were used: control; 60 N - at planting; 60 N - at 30 days after planting; 60 N - at flowering; 20 N - at planting + 40 N - at flowering; 20 N - at planting + 40 N - at 30 days after planting; 20 N - at 30 days after planting + 40 N - at flowering. Randomized complete block desing was used for the laboratory studies, and in the seedbed, blocks at randomized for the field observations, with four replications. In relation to the height of the plants, it was observed a tendency to shorter plants in the traetment control and a tendency to taller plants in the 60 - at planting. However, at harvest the plants had a similar height. The treatments which received N fertilization at planting and 30 days after planting presented a larger diameter, although they were not statistically differents from the others. The green weight of the forage, seed yield, number of seeds per panicle were not influenced by N fertilizer. The control and the 60 N - at flowering treatments showed less number of plants in the stand, indicating that the lack of this fertilizer or late aplications cause a reduction in the plant survival. In general, the N fertilization did not influence a 1.000 seed weight, the first count and the germination percentage. The data had showed that the seedling root lenght ranged from 14 to 16cm; the highest averages were found in the treatments which received N fertilization applied at flowering and 20 N - at planting + 40 N - at flowering and 60 N - at flowering. Seedling vigor showed a tendency to increase when the N fertilization was applied in these periods, although this increase was not very evident. In this way, it was found seedlings with more dry weight in the treatment 20 N - at planting + 40 N - at flowering. On the other hand, the treatments that received N fertilizer at flowering (60 N - at flowering, 20 N - at planting + 40 N - at flowering and 20 N - 30 days after planting + 40 N - at flowering) showed the highest seed protein percentage. However, seed protein per area was not influenced by N fertilizer.