Testing Nitrogen Fertilizer Sources to Increase N-Use Efficiency of Common Beans in the Brazilian Savanna.

Brazil is the world’s largest producer of common beans (Phaseolus vulgaris). In Brazilian savanna, common beans are grown mainly under irrigation throughout winter season. In such conditions, averaged yield is the highest in Brazil (2,297 kg/ha). The cost of production, however, is increasing each year, especially due to application of high amounts of fertilizers. For this reason, there is a demand to increase fertilizer use efficiency. Nitrogen (N) fertilization is one of the most important production factors and urea is the most used source of synthetic N in Brazil. Urea applied under soil surface in no-tillage system, however, results in high losses of N by volatilization of NH₃. Using urease inhibitor and polymers covering urea granules are technological options to reduce N losses. A field study was carried out in a clayey Rhodic Ferralsol, in winters 2009 and 2010, aiming to evaluate the effect of five N fertilizer sources on N losses by volatilization, and on common beans yields. The experiment consisted of six treatments: five N sources (common urea, urea with NBPT urease inhibitor, polymer coated urea, ammonium sulphate, and ammonium nitrate) and one control (with no N addition), in a randomized complete block design with five repetitions. Nitrogen, 80 kg ha^-1, was applied in a single top-dressing fertilization when plants were at V4 stage (three trifoliate leaves). Results showed that urea with NBPT urease inhibitor and polymer coated urea were effective in reducing up to 35% NH₃ volatilization. There was no significant difference among N sources for common beans yields. The apparent fertilizer N recovery was lower in common urea (37%) than in other fertilizers tested (from 51 to 65%). We concluded that all fertilizers tested showed higher N-use efficiency compared to common urea.