The forms of iron extracted by different methods were studied in soils developed on four basement complex rocks within Northern Guinea Savanna of Nigeria namely: migmatite gneisses, older granite, quartzites and mica schists. The study shows that forms of iron generally decreased in the order of total elemental iron (Fe T) determined by XRF > double acid extractable total iron (Fe a) > dithionite extractable iron oxide (Fe d) > oxalate extractable iron oxide (Fe x) > pyrophosphate extractable iron oxide (Fe p) > 0.1M HCl extractable micronutrient available iron (Fe h). Variation in content of total irons (Fe T and Fe a) were not significant in the soils, but content of Fe h , Fe d , Fe x and Fe x/d significantly varied in the soils on the various parent materials. Therefore processes and extent of pedogenesis were considered to influence the variations resulting in recrystallization and increase in content of Fe h and Fe d in these soils. The significant correlation between various forms of Fe (Fe a , Fe d , and Fe x) with active iron ratio further affirmed that as soils on basement complexes increase in their pedogenetic age, Fe content generally increases irrespective of total forms of iron. The strong correlation between Fe T , Fe a and Fe d indicate that these forms of iron were extracted from similar sources.

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Water erosion is a major factor degrading soils of the Nigerian semi-arid ecoregions, and making agriculture less sustainable. For example, soil erosion in the Northern Guinea savanna ecozones of Nigeria is prominent in cultivated areas during the early part of the rain-fed crop production season, when most soil surfaces are bare. In order to estimate the magnitude and timing of soil loss from cultivated lands. Selected herbaceous legumes (Macrotyloma uniflorum, Stylosanthes hamata and Mucuna pruriens) were inter-cropped with maize, a sole maize and a maize/straw mulched treatments were also maintained and evaluated for soil loss control potential. Sediments were collected in 94 liter capacity drums in each treatment. This study was carried out in Zaria (between longitudes 7°30Ј and 7°50Ј E and latitudes 11°00Ј and 11°10Ј N) in 1993 and 1994. Results obtained show that generally, higher sediment yields in 1993 and 1994, were received under legume live mulch and sole maize treatments, than straw mulch. Macrotyloma live mulch however controlled soil loss better than the other legume live mulch and sole maize. Straw mulch, followed by Stylosanthes and Macrotyloma live mulch treatments resulted in significantly higher maize grain yields than sole maize and Mucuna live mulch treatment. Measured and estimated soil loss, and suitable management practices that would ensure sustained productivity of the soils were suggested.