Interspecific interactions of iron and nitrogen use in peanut (Arachis hypogaea L.)-maize (Zea mays L.) intercropping on a calcareous soil

Peanut-maize intercropping is known to alleviate iron deficiency in peanut on calcareous soils by belowground interspecific interactions. However, the underlying mechanisms of these interactions are not fully understood. A two-year field experiment with two nitrogen fertilizer levels was performed on a calcareous soil, to study Fe and N nutrition and yield of a peanut-maize intercrop (IC). In order to identify belowground interspecific interactions, root barriers were employed between adjacent peanut and maize rows. Chlorophyll (measured by SPAD) and active iron concentration in peanut leaves, total Fe and N concentrations, acquisitions, and grain yield were determined. IC increased SPAD values and active iron concentrations in young peanut leaves and alleviated peanut Fe deficiency chlorosis compared with sole-crop (SC) peanut. Total Fe and N concentrations in IC peanut were higher than those in SC peanut, and Fe and N accumulations per plant were also higher than in SC peanut without N fertilizer. IC did not significantly influence Fe concentration in IC maize, but improved N concentration. IC significantly decreased Fe and N acquisition per ha and grain yield of peanut and maize components compared with the respective SC. However, the combined Fe and Ne acquisition per ha in the IC was significantly higher than the weighted mean of the SC systems. The land equivalent ratios (LERFe, LERN and LERgrain) were greater than 1, but decreased to close to 1 with root barriers. Supplying N fertilizer increased grain yield and Fe and N acquisition in the IC, but significantly decreased LERFe, LERN, and LERgrain, confirming that N availability and use are important for determining intercrop advantages. The effect of physical root barriers between rows of peanut and maize indicates that belowground mutual interspecific interactions regarding Fe and N acquisition plays a major role for determining the advantages of peanut-maize IC on calcareous soils.