Resume

The objective of this experiment was to assess the millable stalk yield (SY) and technological attributes of varieties of sugarcane in response to N rates and inoculated diazotrophs. Two trials in non-irrigated areas were set up in Sales Oliveira, Brazil, on March 23 and May 12, 2009, during the plant cane cycle. The experiment was a split plot with four replications. Three varieties of sugarcane were placed in the main plots and the fertilizer treatments in the subplots: control (no N) and the rates 30, 60, and 90 kg N ha-1 applied as urea in the furrow. In addition, a mixture of five species of diastrophic bacteria were inoculated in plants that received no N and 60 kg N ha-1. The subplot consisted of five rows 10 m long, spaced at 1.5 m. The harvesting of unburned stalks was done on August 18, 2010, 17 and 15 months after planting. SY was measured with the aid of a tractor equipped with hydraulic grab and load cell. The technological attributes of stalks sampled were performed in 10 cane stalks randomly collected per plot. Varieties IACSP 95-5000 and SP 81-3250 showed the highest stalk yields in Experiment 1 (126 and 110 t ha-1, respectively). In the 2nd experiment the varieties RB 86-7515 and IACSP 93-3046 stood out: 105 and 103 t ha-1. No effect of inoculation on stalk yields was observed in both experiments. Yields increased by 240 kg ha-1 of cane per kg N (SY = 105 + 0.24N, R² = 0.93) in Experiment 1. The highest stalk yield (105 t ha-1) was obtained with 50 kg N ha-1 in Experiment 2 (SY = 95 +0.402N - 0.004N², R² = 0.99). A marked response do N application was observed and sugarcane varieties responded differently to fertilization but not to inoculation in the cane cycle. Observations will continue in the ratoon crop.