Investigations were carried out into the effects of seasonal changes on some soil chemical properties in the Northern Guinea savanna ecosystem in Nigeria. The study was carried out in Kamuku National Park is located in Birnin Gwari of Nigeria in 2011and 2012. Twenty plots were randomly selected for soil sampling from 100 plots of 10 m × 10 m at four different seasons viz: January (dry season), May (beginning of rains), September (peak of rains) and November (end of rains). Different soil depths were sampled: 0 to 4.9 cm, 5 to 9.9 cm, 10 to 14.9 and 15 to 20 cm at five randomly selected locations. The chemical properties that were mostly influenced by seasonal changes are soil organic matter, total nitrogen, soil pH, available phosphorus, exchangeable cations (Ca, Mg and K), and cation exchange capacity (CEC). The two major seasons that show profound influence on soil properties are dry season (January) and peak of rainy season (September). Soil pH and available phosphorus were higher in dry season (January) and of the beginning of rainy season (May) and remain low at the peak of the rainy season (September). In contrast, soil organic matter and total nitrogen were low in dry season (January) due to burning of the vegetation. However nitrogen content increased at the peak of rainy season (September), due to nitrogen fixation. The increase in the total exchangeable bases (TEB) could be distributed to their importance in the tissue synthesis. There was decline in most soil nutrients during active growth of the woodland savanna trees. Therefore, the limitation of N, P, Ca, Mg, Na and K is most likely to occur in September (peak of rainy season).
Key words: Soil properties, seasonal changes, northern guinea savanna, sampling depths.
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