An evaluation of the universal soil loss equation and field techniques for assessing soil erosion on a tropical alfisol in western Nigeria

Abstract

Four techniques for soil erosion assessment were compared over two consecutive seasons for bare‐fallow plots and a maize‐cowpea sequence in 1985 at IITA, Ibadan, Nigeria. The techniques used were: tracer (aluminium paint), nails (16 and 25), the rill method, and the Universal Soil Loss Equation (USLE). Soil loss estimated by these techniques was compared with that determined using the runoff plot technique. There was significantly more soil loss (P < 0·01) in bare‐fallow than in plots under maize (Zea mays) or cowpea (Vigna unguiculata). In the first season, soil loss from plots sown to maize was 40·2 Mg ha−1 compared with 153·3 Mg ha−1 from bare‐fallow plots. In the second season, bare‐fallow plots lost 87·5 Mg ha−1 against 39·4 Mg ha−1 lost from plots growing cowpea. The techniques used for assessing erosion had no influence on the magnitude of soil erosion and did not interfere with the processes of erosion. There was no significant difference (P < 0·05) between soil erosion determined by the nails and the runoff plot technique. Soil loss determined on six plots (three under maize, three bare‐fallow) by the rill technique, at the end of the season, was significantly lower (P < 0·05) than that determined by the runoff plot technique. The soil loss estimated by the rill method was 143·2, 108·8 and 121·9 Mg ha−1 for 11, 11, and 8 per cent slopes respectively, in comparison with 201·5, 162·0, and 166·4 Mg ha−1 measured by the runoff plot method. Soil loss measured on three bare‐fallow plots on 10 different dates by the rill technique was also significantly lower (P < 0·01) than that measured by the runoff plot. In the first season the USLE significantly underestimated soil loss. On 11, 11, and 8 per cent slopes, respectively, soil loss determined by the USLE was 77, 92, and 63 per cent of that measured by the runoff plot. However, in the second season there was no significant difference between soil loss determined by the USLE and that determined by the conventional runoff plot technique.

Quantification of visual soil erosion indicators in Gikuuri catchment in the central highlands of Kenya

“…Generally, the R L variable is critical since it gives a reflection on the spatial extent of rill erosion (e.g., total length of rills) hence its importance in assessment of the actual total soil loss in the target area. Other authors found that rill erosion played a more important role to overall soil loss amount than sheetwash contribution (Collins and Dunne, 1986;Mtakwa et al, 1987;Govers and Poesen, 1988;Herweg, 1996). Govers and Poesen (1988) stated that the importance of rill erosion to sediment yield was attributed to its progressive increase in supply of sediments to the runoff flow, unlike the sheet erosion that decreased because of the eminent sealing and compaction of the interill areas in time.…”

Preliminary evaluation of pineapple mixed‐cropping systems for protecting reclaimed gulleys in the tropics: An experiment in Southeast Nigeria

“…Soil loss was measured using the graduated nail technique (Mtakwa, et al, 1987); vegetal cover for pineapple and cowpea was estimated using the ring method (Elwell, 1986), and by using a planimeter for the egusi-melon. These were summed for l.OmZ of the cropped area at different stages of crop growth.…”

A review on rill erosion process and its influencing factors

“…However, it is inhibited by the scarcity of available field data that permit the separation of rill and interrill erosion (Govers and Poesen, 1998;Kimaro et al, 2008). It was observed that the importance of rill erosion decreased with time, mainly due to an increase in permeability of the interrill with time though it is not a general phenomenon (Mtkawa et al, 1987). However, the opposite results that the relative importance of interrill erosion decreases with time were presented by other researchers (Govers and Poesen, 1998).…”