AMMONIA VOLATILIZATION, LEACHING OF NITROGEN AND CORN YIELD IN RESPONSE TO THE APPLICATION OF MIX OF UREA AND AMMONIUM SULPHATE OR GYPSUM

The side-dressing fertilization of annual crops should consider S, beside N and K, in order to add protein value to the crop production. This work was carried out in the crop year 2004/2005, in the Farm Floresta do Lobo - Pinusplan, located at the km 93 of BR 050 highway, in the county of. Uberlandia (MG). The experiment was installed in deric Red Latossol typical Cerrado phase cloyed (720 g kg(-1)), with the following objectives: to measure the losses by volatilization of NH3-N from some of the used mixtures at side-dressing in corn crop; to evaluate the distribution down to 60 cm deep, of mineral-N (NH4+-N and NO3-N) and SO42--S after 37 and 51 days of the side-dressing; and evaluate the effect on the corn yield, of granulated mixtures with different particles sizes and N:S ratios, in relation, to area (U) and ammonium sulphate (AS) exclusives. Eleven treatments in randomized blocs design of N:S:K/ertilizers were used in side-dressing, in the corn stage of 5-6 leaves, in the rate of 90 kg ha(-1) off, as exclusive U or AS, or mixtures of U+AS granulated (U+AS(gr)) and U+AS with different size particles (U+AS(fu)) and U+Gypsum granulated (U+Gypsum(gr)) and U+Gypsum powder (U+Gypsum(powder)). The more significant gas losses of NH3-N were in decrecent order: U exclusive 76.8 % followed by U+AS(gr) 37,9 %; U+Gypsum(gr) 27.7 % and AS(fu) exclusive (7.8%). The concentration of ammonium-N and nitrate-N after 37 days of the fertilizer application was similar to the control (without N), demonstrating that the N supplied by the fertilizers were assimilated by the crop, nitrified, leached and, or, adsorbed more deeply. The sulphate-S, at the superficial layer presented the lower concentration in all treatments, reducing its concentration in the layer of 0 to 10 cm, and the 37 to 51 days of the fertilizer applied. After 51 days of the mixtures application, the concentration of total mineral-N was more expressive in the layers of 20 and 40 cm deep, demonstrating the leaching of N from the superficial layers. In the treatments with exclusive application of U and AS this tendency was weaker. In general it had greater ratio of the nitrate-N that of ammonium-N in the total mineral-N in the analyzed layers. In relation to sulphate-S, was expressive increasing the concentration in deeper layers. In stage of flowering, the analysis of nutrients in the leaf opposite the spike showed no significant difference in the ratio N:S leaf, and, this relationship in the shoots of the plant. The highest yields were reached by the treatments of U+AS(fa) and U+Gypsum(gr): 10.285 and 10.241 kg ha(-1) of grains, respectively. The treatments with higher yields were the ones with U+AS(fu) or AS+Gypsum(gr) with the N:S ratios between 2,75 to 4,00. These results allow to conclude that the application of sulphur as side-dressing is necessary and it can be done by mixing U with A or U and Gypsum(gr) although this later one have presented significant higher NH3 losses.