BAHIA FILHO, A. F. C.

COELHO, A. M.

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.8 • li 11 Il O li fil I li 11 li 11 ri li [l 1'1li 11 • 1111 • 11I 1111 li 1'1• lit li 11 ti 11 li • li D I li I li Ü 11 li I.li••li!!•••THE FATE OF NITROGEN IN TROPICAL SOILS. lG.E. FRANÇA* •. lA.M.COELHO ANDIA.F.C. BAHIA FILHO 'Natíona! Maize and Soghum Research Center/EMBRAPA, Sete Lagoas,Minas Gerais, Brazil.•• Nitrogen is one of the major constraints to high cereal productivity in acid soils from the tropics.It is also the most expensive of the three primary macronutrients. Nitrogen use efficiency byplants is low, and due to its high mobility in soil as nitrate, it always represents a potential hazardto the environment, polluting superficial and underground sources of water. Then, it is importantto develop manegment strategies to improve soil and fertilizer utilization and reduceenvironmental contamination .There is already indication that soil and fertilizer nitrogentransformations go slower on acid soils than usually stated. The nitrification rate decreases withpH reduction, causing N- ammonium to stay longer in the soil, reducing nitrate leaching andaffecting plant mineral nutrition. Nitrogen e5N) budget in soil-plant systems, for different soilsand climatic conditions, indicated only small variations on N fertilizers recovery by plants (53 to64%), 56% on average, with the application of 60 to 100 kg of N/ha. The majority of the Nfertilizers was accumulated on the top 0-30 cm soil layer. There was no indication of nitratemoving down the profile. From the measured leaching losses of 10 to 20 kg of N/ha , only 20%were derived from the fertilizer. The great amount of residual N fertilizer imobilization in thesoil upper layers, 70 to 90 %, plays an important role in the total losses of N from the system.Considering the soil-plant system, the total N recovery rate was found to be 85% on average.III•I•fj•11I•I~i!1c", ~11i!~ ~.

The fate of nitrogen in tropical soils.

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