Eight years of eco-intensification of maize-soybean rotation in south Brazil: Maize grain production and nitrogen fertilizer replacement value

The ecological intensification (EI) can reduce the usage of N fertilizers in agriculture by increasing crops diversity, stimulating N fixation, and recycling plant nutrients in soil. In the present study, we aimed to evaluate the EI system compared with farmer practice (FP) and FP with silage (FPS), according to N rate, in the yield of maize and soybean, N agronomic efficiency (NAE), and N fertilizer replacement value (NFRV). A long-term experiment was established in 2011 in Ponta Grossa, Brazil, and evaluated during eight seasons. The treatments were arranged in a split-plot design, with three systems (FP, FPS, and EI) as main plot, and N rate applied to maize as subplot at 0, 70, 140, and 210 kg ha⁻¹, with four replicates. The systems consisted of rotational of maize and soybean in a no-till during summer, with different cover crops and fertilization in winter; in the FP, black oat and wheat were cultivated, white oat and ryegrass in FPS, pea and wheat in EI (without fertilizer). All treatments were duplicated to evaluate the crops in all seasons. The maize yield ranged from 9.3 to 12.6 Mg ha⁻¹ in the eight seasons, where the EI showed higher production than FP and FPS. In the average, the maize accumulated yield (eight seasons) was 5–7 Mg ha⁻¹ higher (0.6–0.9 Mg ha⁻¹ year⁻¹) in EI compared to FP and FPS. The soybean yield was not influenced by the systems or residual N application. The seasons influenced the maize yield, in which the seasons 2017/18 and 2018/19 resulted in the highest maize yield for all systems, and the season 2015/16 showed the lowest. The production of pea aboveground biomass had small variation between the seasons. The NFRV (N saved) for maximum yield was 16 kg ha⁻¹ yr⁻¹ (8 % of N applied) in the FPS, and 79 kg ha⁻¹ yr⁻¹ (38 % of N applied) in the EI, comparing to N required in FP. The NAE was lower in the EI than the FP and FPS and decreased with increase in N rate; e.g., in the season 2011/12, the NAE was 11 kg kg⁻¹ in the EI and 30 kg kg⁻¹ in the FP and FPS. The eco-intensification system resulted in higher maize yield and lower N required compared to FP, which can be strategic to increase crop yield, reduce N application, and moving towards regenerative agricultural systems.