Accepted 24th October, 2016
The primary objective of the current study was to investigate the effect of cutting isolated Acacia tortilis on soil fertility and herbaceous understorey nutrient quality in a truncated ecosystem in south central Kenya. The hypotheses tested revolved around the premise that microenvironmental gradients in nutrients within and without Acacia tortilis are central to explanations of differences in nutrient quality of shade adapted and sun adapted C4 grasses. Standard scientific methods were used to evaluate changes in soil fertility and nutrient quality of Panicum maximum (shade adapted), Chloris roxburghiana and Themeda triandra (sun adapted). A randomized complete block design was used to measure the treatment effects created by cutting Acacia tortilis trees on soil mineral content and nutrient quality of the C4 grasses. Descriptive statistical parameters were used to determine the presence or absence of Acacia tortilis effects on nutrient relations. Mean soil mineral content for the canopy microsites were, nitrogen (0.2%), carbon (2.0%), phosphorous (22.0%), potassium (1.76me/100g), magnesium (3.15me/100g), calcium (6.0me/100g), manganese (0.30me/100g), compared to nitrogen (0.33%), carbon (2.1%), phosphorous (35.5ppm), potassium (1.95me/100), magnesium (4.20me/100g), calcium (6.8me/100g) and manganese (0.42me/100g) in the non-canopy microsites. Higher levels of mineral elements were reflected in the higher levels of nitrogen (2.23+_0.5262), phosphorous (0.17+_0.0239), potassium (2.83+_0.6052) in plant tissues of Panicum maximum compared to nitrogen (1.4 +_0.243), phosphorous (0.16 +_0.038) and potassium (1.6+_0.323) in plant tissues of Chloris roxburghiana in the open grasslands. These results of Acacia tortilis-Panicum maximum interactions suggest that induced disturbances created by clearing of Acacia tortilis trees in the long term will cause shifts in nutrient relations with significant implications on nutrient quality and productivity of C4 grasses.
Keywords: Acacia tortilis, Panicum maximum, nutrient quality, truncated ecosystems.