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oil organic carbon (OC), nitrate (NO3) and iron (Fe) can be highly variable in the tropical humid, acidic environments and such environmental constraints could determine crop physiological development and yield formation.The objectives of the study were to examine the spatial variability of soil OC, NO3 and Fe ions in a tropical peanut-cassava intercropping system and to increase peanut plant nodulation, peanut-yields and nitrogen fixation capacity in the delineated soil OC, NO3 and Fe overlaid management zones.The 2-year field study was conducted during 2013-2014 in the tropical Hainan Island on a Red loamy soil, classified as an Oxisols in the US Soil Classification System.Prior to the planting, the soils were sampled (0-0.2 m in depth) in a 1.5×10-m grid in each plot (n =48) across the field.The experimental treatments, consisted of three rates of rhizobial inoculants (0, 8 and 16 g kg-1), four rates of N fertilizers (0, 30, 60 and 90 kg ha-l) and a control for peanuts (non-intercropping with cassava), were arranged with four replicates in a split-plot design in the field.Peanuts (Arachis hypogaea) cv.'Guihua-68' were seeded within two rows of cassava (Manihot esculenta) cv.'Huanan-9'.The chemical analyses revealed that the soil was typically acidic (pH 5.13) and deficient in OC (6.02±0.17 g kg-1), NO3 (4.89±0.21 mg kg-1) and Fe (9.22±0.33 mg kg-1), as the soil was derived from granite and igneous rocks under hot, humid climate conditions.The interpolated maps showed that spatial patterns for soil OC, NO3 and Fe ions trended to be comparable with high concentrations distributed from north-west (NW) to south-east (SE) across the field.In this NW-SE zone with high OC, NO3 and Fe concentrations (> mean values shown above with standard errors), peanut plant chlorophyll synthesis, root nodulation and total N and Fe uptakes were significantly higher (P < 0.05) than in the north-east (NE) zone where was low in soil OC, NO3 and Fe concentrations due to the limited soil water holding because of a topographically inclined slope.Rhizobial inoculant and N input treatments increased significantly peanut root nodulation, total N/Fe uptake and plant N derived from N fixation (P < 0.05) in the NE zone where soil OC, NO3 and Fe ions were mostly deficient.Yet, soil Fe ions could explain more significantly (42%) of differences in peanut plant derived N fixation in the NW-SE zone than in the NE zone.It was suggested that using soil organic carbon, nitrate and iron overlaid spatial patterns could be useful for N and Fe management for increasing peanut root nodulation and N Fixation.