Abstract
The objective of this work was to evaluate the effects of soil management systems, cover crops, and phosphate fertilization on soil humic fractions in a long-term experiment. The treatments consisted of conventional tillage and no-tillage with pearl millet (Pennisetum glaucum) or velvet bean (Mucuna aterrima) as cover crops, at two doses of phosphorous: 0 and 100 kg ha-1 P2O5 per year. Soil samples were taken 11 years after the establishment of the experiment and analyzed for soil total organic carbon and carbon content of humic fractions at 0.00-0.05, 0.05-0.10, and 0.10-0.20-m depths. The humic fractions are sensitive to soil management, except free fulvic acid, which was the only one that did not reduce its carbon contents on the surface layer (0.00-0.05 m) with conventional tillage. The main changes occurred on the soil surface layer, in which the no-tillage system with pearl millet as a cover crop provided the highest carbon levels in humic fractions. Long-term phosphate fertilization under no-tillage, with pearl millet as a cover crop, promotes the accumulation of organic carbon in soil humic fractions.
Index terms:
humic fractions; no-tillage; organic matter fractions; phosphate fertilization; soil fertility; soil quality
