HUMIC SUBSTANCES AND PHOSPHORUS FRACTIONS IN AREAS WITH CROP-LIVESTOCK INTEGRATION, PASTURE AND NATURAL CERRADO VEGETATION IN GOIÁS, BRAZIL

Crop-livestock integration (CLI) coupled with a no-till planting system (NTS) has proven to be an important alternative farming system, promoting efficient land use and soil conservation by maintaining soil organic matter (SOM). The present study quantified the humic fractions of SOM and soil P fractions and analyzed their relationship in CLI, pasture and natural Cerrado areas in Goiás, Brazil. The samples were obtained from a pasture area (covered with Urochloa decumbens grass for 15 years); a CLI area (planted in annual rotation with Urochloa ruziziensis for 13 years); and a native Cerrado area, sampled for comparison purposes. Total organic carbon (TOC) and carbon in the fulvic acid fraction (C-FAF), humic acid fraction (C-HAF) and humin (C-HUM) were evaluated at a depth of 0‑5; 5‑10; 10‑20 and 20‑40 cm; and inorganic (IP) and organic (OP) P fractions at a depth of 0‑5 and 5‑10 cm. The highest TOC values, humic fractions and OP were found in the Cerrado area. Similarities in relation to the humic fractions and TOC were found between CLI and pasture areas in all the layers between 0 and 40cm. The area currently managed with CLI, but originally covered by Cerrado, had already developed chemical stability (C-FAF, C-HAF, C-HUM and TOC) that was similar to that found in the Cerrado area at a depth of 20-40 cm and with higher C-FAF and C-HUM accumulation compared to the pasture area. Compared to pasture and Cerrado, the CLI system favored the increase in labile, moderately labile and moderately resistant P, both for total P (TP) and IP. IP fractions were found in areas treated with high doses of phosphate fertilizer, whereas OP fractions corresponded to those under low or null anthropogenic influence. Organic P fractions were directly related to the humic SOM fractions.