Influência das adubações orgânica e mineral contínuas sobre as características das frações das substâncias húmicas do solo

Abstract

Com o objetivo de estudar o efeito da aplicação, durante onze anos consecutivos, da adubação mineral e orgânica nos teores de carbono das frações das substâncias húmicas (ácidos fúlvicos, ácidos húmicos e huminas) e carbono total, a duas profundidades, utilizou-se um ensaio instalado no campo experimental da Universidade Federal de Viçosa, no município de Coimbra-MG, em um Podzólico Vermelho-Amarelo Câmbico. Os tratamentos foram formados pela combinação de três níveis de adubação mineral (0, 250 kg/ha/ano de 4-14-8 + 100 kg de sulfato de amônio em cobertura e 500 kg/ha/ano de 4-14-8 + 200 kg de sulfato de amônio em cobertura), dois níveis de adubação orgânica (0 e 40 m^3/ha/ano de composto orgânico) e duas profundidades (0 a 20 cm e 20 a 40 cm). A partir dos resultados obtidos, foi possível chegar às seguintes conclusões: a) a aplicação de 40 m^3/ha/ano de adubo orgânico, durante onze anos consecutivos, aumentou os teores médios de carbono das substâncias húmicas e o carbono total, independentemente da adubação mineral; b) a aplicação de 250 kg/ha/ano de 4-14-8+100 kg de sulfato de amônio provocou maior aumento no teor de carbono nas frações de ácido fúlvico e húmico. Porém, a dosagem de 500 kg/ha/ano de 4-14-8+200 kg de sulfato de amônio, teve efeito depressivo sobre os teores de carbono destas frações.

The continuous combined application of organic and mineral fertilizers during several consecutive years on a given area may cause chemical, physical and biological property changes in soil. A quantitative analysis of the carbon contained in the humic acid, fulvic acid and humine fractions as well as in total carbon was carried out at a farming area in Coimbra~MG, to study the effects of compost and use of mineral fertilizer on humic substances. The area studied is owned by the Federal University of Viçosa’s Experimental Farm and has hem receiving the same fertilizer treatment for 11 years. The soil is a clayey cambic red yellow podzolic. The experiment was arranged in a randomized block design with four replications under a 3 x 2 x 2 factorial scheme: three mineral fertilizer levels (0, 250 kg/ha/year of 4-14-8 + 100 kg of ammonium sulphate as side dressing and 500 kg/ha/year of 4-14-8 + 200 kg of ammonium sulphate as side dressing, two levels of organic fertilizer (0 and 40 m^3/ha/year of organic compost) and two depths (0 to 20 cm and 20 to 40 cm). Fertilization was carried out manually on 15 cm deep furrows. Statistical analysis showed that there was a significant effect of the organic fertilizer levels, depth and organic fertilizer x dwth interaction for all the humic fractions and total carbon. There was also a significant effect for the humic and fulvic acid fractions in relation to the mineral fertilizer levels as well as to the mineral fertilizer x organic fertilizer interaction. For the mineral fertilizer x depth interaction, there was a significant effect only for the humic acid fraction. There was no sigrificant difference in the interaction of the three factors (mineral fertilizer x organic fertilizer x depth). The results show that the compost application of 40 m3/ha/year during 11 consecutive years increased the average content of carbon in the humic substances and total carbon regardless of mineral fertilization. The application of 250 kg/ha/year of 4-14-8 + the nitrogen fertilizer as side dressing provided the highest increase in the content of the humic and fulvic acid fractions, with a decreasing effect for these two fractions at the levels of 500 kg/ha/year of 4-14-8 + nitrogen fertilizer as side dressing.