Nitrogen losses mitigated with maize–legume intercropping in the Yucatan Peninsula

In recent years, nitrate leaching and environmental impacts from agriculture have become global issues, due in part to the increased use of nitrogen (N) fertilizers in agriculture. In the Yucatan Peninsula, intercropping is a traditional farming practice known as the “Milpa” system (i.e., a traditional farming practice characterized by the simultaneous cultivation of maize [Zea mays L.], beans [Phaseolus spp.], and squash [Cucurbita spp.] in the same field). A field experiment was carried out in the region to determine the effect of maize–legume intercropping systems on potential N losses compared to sole maize cropping systems. The investigation was conducted in a vertic Cambisol, which is primarily composed of clay. The treatments included maize intercropped with the traditional legume, cowpea (Vigna unguiculata (L.) Walp.), maize intercropped with a novel legume for this system, sunn hemp (Crotalaria juncea L.), and sole maize as the control. At harvest, soil nitrate content was greater in the deepest layers (30–60 cm) in the maize monocropping system compared to the intercropping system. No significant differences were observed in terms of soil ammonium concentration between the two systems. Overall, the maize/legume intercropping system reduced total mineral N (ammonium + nitrate) concentrations by a range of 27% and 53% in the deepest layers of soil (30–60 cm and 60–90 cm, respectively) compared to the monocropping system. Thus, maize/sunn hemp and maize/cowpea intercropping can sustainably reduce N loss in the deeper soil layer and potentially reduce nitrate leaching. This study also found that a maize/cowpea intercrop not only reduced N concentrations in deeper soil layers but also maintained maize yield when compared to a sole maize cropping system. Additional research is needed to determine the mechanisms by which intercropping can reduce potential nitrate leaching while still maintaining crop yields and other ecosystem services.