Effect of Topographic Position and Seasons on the Micronutrient Levels in Soils and Grown Huckleberry (<i>Solanum scabrum) </i>in Bafut (North-West Cameroon)

Abstract

Although topography and climate are known to affect soil micronutrient mobility, some related aspects like micronutrient bioavailability to plants and implications to human intake are not fully understood. This paper aimed to study the effects of different topographic positions and seasons (dry or humid) on micronutrient levels in soils and Solanum scabrum. A randomized complete block design with four replications was adopted for each topographic position. Fieldwork was completed by a battery of soil and vegetable analyses. The main results revealed that soil micronutrient levels appeared as follows: Al>Fe>Mn>Zn>Cu for all positions and seasons. The soil micronutrient levels were lowest for the midslope in relation to its steeper gradient that affects downwards migration of matter. Zn and Cu were below the recommended range for agricultural soils, while Al was far above in relation to the strongly acidic pH. In S. scabrum, micronutrients appeared as Mn>Fe>Zn>Al>Cu. Globally, vegetable metal levels were higher in the dry season for all positions. Except Al, all metals were below permissible and toxicity levels in food, while only Fe, Mn and Zn where above recommended range for normal plant growth. Metal transfer factors, apart from midslope, were higher in the dry season. Only Mn and Zn for all positions and seasons as well as Zn at footslope, were above 1. Globally, micronutrient levels in soils and vegetables were higher in the dry seasons for all positions. Micronutrient intake rates were higher in the dry season for all positions but lowest in the midslope for all seasons. Except Fe and Zn in adults, metal levels were above the recommended daily dietary intake indicating excess micronutrients intake by the inhabitants. Overall, a combination of steep slope and humid season reduces soil micronutrient level, limit uptake by vegetables and hence reduce mean daily intake in humans.