Nitrogen (N) is an element absorbed in larger quantities by plants due to the vast number of chemical and biological reactions. Despite the high nutritional need of this element by the plants, it is not a constituent of any terrestrial rock. To avoid high production costs of N, there is an increasing interest in the use of organic fertilizers in Brazil, including the use of humic substances (HS). In this work we evaluated the chelating properties of HS, when used together with a source of N. The nitrogen source used in this experiment was the ammonia. We checked the optimum conditions for interaction between the HS and ammonia such as: the ratio of reaction of each compound;minimum incorporation time between these compounds and the amount of ammonia that can be adsorbed by HS (income). The best ratio of ammonia/HS was 1/50 (v/v). Higher amounts of ammonia added to 50 mL of HS caused a greater loss of N. We also concluded that the application of ammonia/HS in the soil can be made immediately after their mixing, without the need of higher contact time between these substances in order to have the adsorption. No loss of ammonia was detected after 72 hours of its application together with HS. Finally, by using a factorial design, the best working area was found by settling the time of incorporation and volatilization in 24 h, and the volumes of HS and NH3 in 100 and 2 mL, respectively.
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