Agronomic efficiency of nitrogen associated with humic acid in sugar cane

Abstract

The shift in the system of sugarcane harvesting without previous burning promotes accumulation of sugarcane straw, creating difficulty in the nitrogen (N) fertilizer management due to limitation in fertilizer incorporation which can lead to N losses from the system. The use of humic acid (HA) associated with urea fertilizer has had several benefits for plant growth, although few studies have been conducted nowadays. There is evidence that occurs a synergistic effect when associating HA and N, because the HA reduce the assay of the urease enzyme, which is responsible for the urea hydrolysis, thereby avoiding losses of N by volatilization. The objective of this study is to evaluate the efficiency of applying urea fertilizer associated with HA extracted from peat. The tracer isotope technique with 15N will be used to evaluate the urea-N fertilizer efficiency in sugarcane. A field experiment will be carried out in a sugarcane production area. Treatments will consists of HA rates (0, 150, 300, 450 and 600 L ha-1 or 5.4, 10.8, 16.2 and 21.6 kg ha-1 Total Organic Carbon-TOC present in the AH), urea-N rates (0, 25, 50, 75 and 100 kg N ha-1) and urea-N rates associated with the AH rates described above. Additionally, an control treatment will be installed. A randomized block experimental design with six replicates will be adopted. The trial will be conducted during two sugarcane crop cycle (ratoon). In the first ratoon crop cycle (2011/2012) it will be evaluated: N-NH3 volatilization from urea rates associated or not with humic acid, the sugarcane yield, quality parameters and nutrient extraction in the final harvest. In the second ratoon crop cycle (2012/2013), the same measurements will be performed in addition to quantifying the rate of biomass and nutrient accumulation over time. For this analysis, five sampling will be performed during the crop growth cycle, allowing evaluate the recovery of urea-15N over time by the 15N isotope tracer technique. Additionally, soil samples will be collected in the 0-10 cm layer and taken to the laboratory, where another test will be carried out to evaluate the enzyme urease activity, the rate of mineralization and nitrification.