Management of nitrogen fertilization in sugarcane and diagnosis using crop canopy sensors

The application of N-fertilizer without standardization stage of plant growth results in decrease of nitrogen use efficiency (NUE) and increase the environmental impact. The use of crop reflectance sensor that evaluating the sugarcane nutritional diagnosis has been widely used by researchers in other agricultural crops than sugarcane, probably due to the difficulty of diagnosis of the nutritional status of the crop in nitrogen (N). Thus, this research project was the hypotheses: the diagnosis of crop nutritional status through crop canopy reflectance sensor are efficient to predict the rate of N-fertilizer to be applied in the field. The main objective of this research was: evaluate the nutritional status of the sugarcane crop fertilized with different nitrogen rates applied at different times after harvesting through crop canopy reflectance sensors to generate parameters for sustainable application of N- fertilizer in the fields. Three experiments will be installed with the same experimental design, in commercial sugarcane fields, all in the same cycle (first ratoon) using the same variety, but harvested at different periods (begin, middle and end crop season) within the sugarcane season in center south region of Brazil. The experimental design was a randomized block with split plot in four replications, that in the plots were different periods of N application after the sugarcane harvesting (0, 30, 60, 90 and 120 days after the harvest- DAH), and in split plots were five N rates (0, 50, 100, 150 and 200 kg ha-1 N). During the development of the crop (30, 60, 90, 120, and 150 DAH) it was evaluated the biometric analysis (population and height of tillers, number of green and dried leaves), and evaluate the N crop nutritional status by SPAD index in TVD leaf (SPAD chlorophyll meter), and the crop canopy reflectance sensor (ACS 430 - Crop Circle Holland Scientific). There were differences in sugarcane yield between the experimental fields harvested at begin, middle and end crop season, with the best yield in begin harvest area. The N application period had major impact on crop productivity, and invariably the greatest response to nitrogen fertilization was obtained when there was no water stress: determining factor in increasing the nitrogen fertilization efficiency. The best N-rates were 100 and 120 kg ha-1 N respectively, to experiment harvest at the beginning / end and at the middle of crop season. The best time to use the crop canopy reflectance sensor is associated with lack of water stress, beyond the sugarcane fields present in field conditions, average height (insert TVD leaf) from 0.4 to 0.6 m, tillers booth 15 to 20 tillers per meter, and 6 to 8 green leaves. In this context, the harvest period associate with the climate conditions are important to help in a decision about the best period to apply the N fertilizer and crop reflectance sensor is a tool to evaluate the nutritional diagnosis of sugarcane crop (AU)