Influência da adubação nitrogenada sobre bioindicadores de qualidade do solo

Abstract

Urea is the nitrogen fertilizer most used in Brazilian agriculture, due to the low cost and high percentage of nitrogen (N) offered, in relation to other fertilizers. The corn crop has high requirements for N, being this essential for a good establishment of the crop and, therefore, can be a limiting factor in production. In recent years, increases in the productivity of corn crops are also associated with the growing increase in fertilizer consumption. In view of this situation, it is important to verify whether the application of the commercially recommended doses of urea, in different soils, may cause some interference in the life of organisms that are indicators of soil quality, such as earthworms and collemboli. For this, Eisenia andrei earthworms and Folsomia candida collemboli were exposed in two types of soil (Neossolo and Latosol) treated with increasing concentrations of urea, in laboratory ecotoxicological tests, following the recommendations of ISO 11267 and ISO 11268-2. The concentrations used in Neossol were 0 (control), 65, 87, 174, 304 and 608 kg of urea / ha¹ and in Oxisol: 0, 65, 87, 130, 260 and 520 kg of urea / ha¹. The results showed that there were differences in urea toxicity when applied to different soils and species. For E. andrei, the molecule showed significant reductions in reproduction even at the lowest dose in Neossolo (EC50= 103 kg/ha), whereas in Latosol the effect was only significant at the highest tested dose (EC50= 347 kg/ha), however this dose completely inhibited the reproduction of the species. For F. candida, the toxic effect of urea was already significant in the first dose tested in Latosol (EC50= 62,2 kg/ha), while in Neossolo (EC50 =219 kg/ha), effects were observed in the two highest doses tested, in which the reproduction of the species was totally inhibited. Thus, although the organisms demonstrate different sensitivities to urea, it is evident that the type of soil interferes in the toxicity, especially when exposed to overdoses. These results point to the need for further studies with other organisms representative of soil fauna, other types of soil, as well as in other test conditions, in the field or semi-field to verify whether these results persist in real environmental situations.