Fertilizantes nitrogenados convencionais, estabilizados, de liberação lenta, controlada e blends para o cafeeiro

Abstract

Urea is the most used source of nitrogen fertilizer used in coffee crops. When applied to soils, it comes into contact with water and suffers a hydrolysis reaction catalyzed by the urease enzyme. During this process, part of the nitrogen is lost to the atmosphere. We conducted this research with the objective of quantifying the loss of ammonium through urea and seeking more efficient nitrogen fertilizers to evaluate stabilized nitrogen fertilizers of slow and controlled release, comparing them to conventional fertilizers used in coffee crops. The study was conducted in Lavras, Minas Gerais state, Brazil. We used a completely randomized block design, with 11 treatments and three replicates. The stabilized and conventional fertilizers evaluated were: conventional urea, urea dissolved in water, ammonium sulfate, ammonium nitrate, urea + copper + boron, urea + anionic polymer, and urea + NBPT. Another group of fertilizers with slow or controlled release technology was also evaluated: urea + sulfur + polymer, urea + plastic resin, formaldehyde urea, and urea coated with a water-insoluble polymer. We applied 300 kg ha -1 of N/year for all treatments, dividing the conventional and stabilized fertilizers into three plots, and the slow or controlled release fertilizers in a single application. We evaluated the loss by volatilization, pH change in the surface layer of the soil, the contents of N, S, Cu, and B in the leaves as well as coffee productivity. In the 2016/2017 harvest, the highest losses of NH3 occurred for urea + anionic polymer (30.6%) and conventional urea (25.6%). The lowest loss of nitrogen by volatilization occurred for ammonium nitrate (0.5%), ammonium sulfate (0.6%), and formaldehyde urea (0.3%). The pH of the surface layer of the soil did not alter after applying the nitrogen fertilizers. The highest foliar contents of N occurred for the fertilizers presenting the lowest losses of ammonium: ammonium nitrate, ammonium sulfate, and formaldehyde urea. Eight of the fertilizers allowed productivity between 60.5 and 69.2 bags ha -1 . The lowest productivities occurred for ammonium nitrate, formaldehyde urea, and urea + copper + boron (from 46.8 to 53.5 bags ha -1 ). We observed no increase of productivity for the fertilizers presenting the lowest losses of N by volatilization. When compiling research data obtained by authors who previously worked in the same experimental area for four harvests, we observed a higher loss for urea + anionic polymer (33.0%), followed by conventional urea (29.5% of loss). The lowest losses occurred for ammonium nitrate (0.4%), ammonium sulfate (0.6%), and formaldehyde urea (0.7%). The average productivity of the experiment in four harvests was of 37 bags ha -1 . The fertilizers with the highest average were urea + anionic polymer (42), urea + plastic resin (41), ammonium sulfate (41), dissolved urea (39), conventional urea (38), urea + NBPT (37), and urea + sulfur + polymer (37).