Soil C and N fractions across soil depths in an ecological intensification system of maize-soybean rotation in Southern Brazil

Eco-intensification (EI) system can improve farmer practice (FP) sustainability. This study aimed to evaluate the effects of long-term cultivation systems and N rate on soil C and N fractions and to correlate with soil C and N stocks. The hypotheses were that N fertilization reduces labile soil C and N contents, especially in the EI system compared to FP, which is associated with higher total C content and C stock, and that high N rates would increase NO 3 - movement in soil profile, especially in the FP. A field experiment was conducted over eight years using a split-plot design with two systems (FP and EI) in the main plot and four N rates (0, 70, 140, 210 kg ha -1 ) in the subplot. Both systems consisted of a no-till soybean-maize rotation with different winter crops: Wheat-oat was cultivated under FP and wheat-pea under EI. Soil was sampled up to 100 cm depth and analyzed for total N (TN), total C (TC), inorganic N, dissolved organic N (DON), mineralizable C (MINC), permanganate oxidizable C (POXC), and N -acetyl-β-D-glucosaminidase (NAGase) activity. EI system resulted in lower POXC (20–40 cm) and MINC (0–10 cm) contents compared to FP. NAGase activity, which is –related to soil C accumulation, –was higher under EI than FP. NO 3 - content at 40–80 cm depth was lower in EI than in FP, suggesting lower NO 3 - accumulation in deeper soil. The findings suggest that the EI system promotes long-term soil carbon sequestration by favoring C stabilization rather than rapid turnover.