Nitrogen (15N) use by sugarcane submitted to nitrogen fertilization with "leaf spray" (N-Urea) as a complement to the soil nutrient application

Abstract

The nitrogen fertilizer use efficiency (NUE) by sugarcane ratoon is low when this nutrient is applied on the soil (average of 25%), while it is high (reaching 85%) when nitrogen (N) is applied on the sugarcane leaves. The N application on sugarcane leaves decreases the nutrient losses nevertheless the N fertilization on soil is needful due to its importance in the initial stages of sugarcane ratoon development. In this context, the project aim to evaluate the NUE (in two locations under contrasting soils) with the N application on the leaves of sugarcane ratoon harvested in the early of the growing season as a complement of the soil nitrogen fertilization. In addition, the sugarcane stalk yield and technological attributes will be harvested in six locations of which two at the beginning, two in the middle and two in the final of growing season. The field trials will be carried out in randomized complete blocks with 15 treatments and four replicates. The treatments will include N rates applied on soil (S) and leaves (L), S + L: 40 + 0, 60 + 0, 80 + 0, 120 + 0, 160 + 0, 0 + 15, 0 + 30, 0 + 45, 40 + 15, 40 + 30, 40 + 45, 60 + 15, 60 + 30 and 60 + 45 kg N ha-1, and a control without nitrogen fertilization. Microplosts for 15N-urea application on leaves will be installed in fields that will be harvested at the beginning of growing season. During the growing season will be evaluated: NUE, macro and micronutrients accumulation, SPAD index, urease and glutamine synthetase activity in the plant aboveground and mineral-N in the soil. At harvest, beyond of above mention evaluation will also be evaluated sugarcane stalk and sucrose yield. An experiment will also be conducted under greenhouse conditions with N rates (5, 10, 15 and 20 kg N ha-1) applied on sugarcane leaves to evaluate the biomass accumulation, NUE and translocation of N-fertilizer in the crop. In addition, the following evaluation will be conducted in leaves: the anatomical and morphological transformations, chlorophyll content and urease and glutamine synthetase activity. Prior to the mentioned experiments will be quantify the stomata number on the adaxial leaf face in the upper sugarcane leaves of the 14 most cropped sugarcane cultivars in Brazil and the anatomical analysis of these leaves to definition the cultivars that will be used in the experiments.