Seasonal Variability in Runoff, Sediment and Nutrient Losses in Vegetation Fallows in The Rainforest Zone of Southern Nigeria

Abstract

The study assessed seasonal trend in erosional losses on natural fallow vegetation of varying ages in a part of the rainforest zone of Nigeria. Measurements of runoff, sediment and nutrient losses, basically organic carbon (OC) and total nitrogen (TN) were made for the months of March to November in 2012 rainy season using runoff plots of 40 m². The highest erosional losses across the plots were observed during months of heavy storms, precisely July, August and September. The 5yr-old plot experienced the highest loss of nutrient (OC: 52.2%, TN: 52.9%), followed by the cultivated farmland (OC: 31.8%, TN: 31.2%), while the 10yr-old and 3yr-old fallows experienced the lowest losses of 3.5%, 3.3% and 12.5%, 12.6% in OC and TN respectively. Monthly volume and quantities of sediment varied significantly among the treatments (p < 0.05). The study recommends early cessation of weeding during the commencement of the dry season because it strips the soil of some protective cover for subsequent season.