Ammonia Volatilization Following Surface Application of Nitrogen Fertilizers to Corn in No Tilage.

The technologies added to urea have been evaluated with goal to reduce volatilization in no tillage. Zeolite due to high cationic exchange capacity, urea coated with boric acid and copper sulfate due to acidity and similar frame between urea and boric acid plus B competitive inhibition and Cu no-competitive, and further mixtures with ammonium sulfate.

The experiment was a randomized complete block with four replications to evaluate ammonia volatilization from 100 kg ha^-1 of N as urea, urea+zeolite (15% m/m), ammonium nitrate, urea coated with boric acid (0.4% B) and copper sulfate (0.14% Cu), mixtures of ammonium sulfate (33.3%) + urea (66.7%) and ammonium sulfate (33.3%) + urea coated (66.7%) and a control (without N) in surface application in 2010 under corn residue and  2011 under soybean residue.

In the 4, 8, 12, 16 and 20^th day after fertilizers application ammonia quantification was obtained through direct method with semi-open collector used in dynamic form with application of collector efficiency factors.

Quantities of NH₃-N volatilized were lower than 20% of total N applied in both experiments. The volatilization was relatively lower compared to literature with 50 to 94% in surface application in soils with straw coverage.

Contrast analysis determined that ammonia volatilized from urea coated was 7.9 kg ha^-1 lower than others treatments with urea (p<0.01) in 2010. However, the high and often rainfall after the fertilizers applications in 2011 caused no difference among treatments based to urea.

Peaks of ammonia volatilization occurred in the first days after application of all treatments. Hydrolysis speed and consequently ammonia volatilization depend on humidity conditions of soil. In conclusion, urea coated with boric acid and copper sulfate showed lower peak of NH₃ volatilization among the treatments, with exception of ammonium nitrate in 2010.