The objective of this study was to evaluate the agronomic characteristics of Nopalea cochenillifera (L.) Salm-Dick under different frequencies and levels of nitrogen application (N). Three nitrogen fertilizer application frequencies (1 time year-1, 6 times year-1 and 12 times year-1) and four nitrogen levels (0, 100, 200 and 400 kg of N ha-1 year-1) were evaluated one year after the planting, in a randomized blocks design with 12 replications. There was no interaction (P>0.05) between application frequencies and nitrogen levels. The number of cladodes, and the green and dry forage mass yields of the cactus pear were higher with the application frequency of 6 times year-1, presenting 18.4 ± 2.0 cladodes per plant, 151.0 ± 17.8 and 9.8 ± 1.0 t ha-1, respectively. The yield doubled with the application of 400 kg N ha-1, when compared to the treatment with no nitrogen application. With the nitrogen application frequency of 1 time year-1 the crude protein and neutral detergent fiber contents were higher, presenting 4.0 ± 0.1% and 33.8 ± 0.5%, respectively. When nitrogen is applied 6 times year-1 it provides higher growth and yield, but lower protein and fiber contents. The level 400 kg N ha-1 provides higher yield and lower nitrogen use efficiency.

The objective of this study was to assess the agronomic and nutritional responses of Carajás grass (Cenchrus purpureus × C. americanus, syn. Pennisetum purpureum × P. glaucum, cultivar ‘Carajás’) fertilized with protected urea. The experimental design was completely randomized blocks in split-plot arrangement over time. The treatments consisted of 5 levels of nitrogen (0, 100, 200, 400 and 800 kg N/ha/year) and measurements were made over 2 seasons (spring 2015 and summer 2016), with 8 replicates. Leaf and stem elongation and senescence rate of tillers increased as N dosage increased, while tiller density, leaf:stem ratio, live:dead material ratio and phyllochron declined. Forage biomass increased with N dosage reaching 47 t DM green forage/ha at 800 kg N/ha but DM production per unit of N applied declined dramatically as level of N applied increased. There was no effect of season. For crude protein (CP) and fiber concentrations, a positive effect was observed with increasing N application, with maximum CP% of 172 g/kg with 800 kg N/ha in spring. Further studies are warranted to determine if economics indicate that the higher fertilizer levels are justified and even protected urea should still be applied on a number of occasions, but still less often than conventional urea, rather than as a single dose at the beginning of spring.