**3.1 Factors affecting runoff and soil loss**

Table 2 shows the value of soil loss for the three soils. Soil loss decreased with increasing peat contents for all combinations of soil type, rainfall duration and compaction effort. Soil loss also decreased with increasing compaction effort and increased with increasing rainfall duration. Soil loss was consistently highest in the sandy soil, intermediate in the clay soil and lowest in the clay loam soil. Table 3 shows that cumulative runoff increased with increasing rainfall duration and compaction levels but decreased with increasing peat content. Runoff was highest in the clay, followed by clay loam and lowest in the sandy loam soil.


aValues are means of two replicates.

Table 2. Soil lossa (kg) for three soils with and without peat compacted and exposed to four rainfall durations

Table 4 summarizes the mean values of cumulative runoff and soil loss for the different experimental factors. Mean runoff increased with increasing clay content, compaction effort and rainfall duration but decreased with increasing peat content. For soil loss, mean values of soil loss varied from 1.36 kg in the sandy soil to 0.95 kg in the clay loam soil. The analysis of variance (Table 5) showed that the main effects of soil type, peat content, compaction effort and rainfall duration were all significant (P = 0.001) for the two parameters as depicted by the 'F' values. Rainfall duration was the most important factor that affected the two parameters. In addition, the most significant interaction that affected the two parameters was that between soil type and rainfall duration which was significant at 0.1% level. This was followed by the interactions between compaction effort and rainfall duration and between peat content and rainfall duration in that order for the two parameters. These interactions and the main effects will be described below.

Soil Loss-Rainfall Duration Relations as Affected

matter originating from grass.

**3.1.2 Soil type** 

runoff rates.

by Peat Content, Soil Type and Compaction Effort 185

1987). Although soil strength is known to increase the resistance of soils to erosion (Rachman et al., 2003; Wuddivira, 2008), the present results further confirm that peat reduces soil loss by increasing infiltration and decreasing runoff during rainfall rather than by strengthening the soil as was obtained for other organic materials like farmyard manure by Wuddivira et al. (2009) and Ekwue et al. (2009). Runoff and soil erosion are important not only for soil and water conservation, but also to reduce nutrient discharge with runoff (Bjorneberg et al., 2000). This means that the reduction of surface runoff and soil erosion by peat will not only aid soil conservation, but also reduce loss of plant nutrients in the soil. The interaction between peat content and rainfall duration (Fig. 3) shows that the effect of peat on soil loss increases with rainfall duration. A similar interaction was reported for soil detachment by Ekwue (1991) in connection to organic

The main effect of soil type was the second most important of all the experimental factors on soil loss and runoff (Table 5). This was almost like the previous paper by Ekwue and Harrilal (2010) where it was the most important factor. This may be as a result of the same process involved in the raindrop erosion measured in the two studies. In a previous study by Ekwue et al. (2009), soil type was the least important factor and this may be because this study measured wash erosion by surface runoff, while the present and the Ekwue and Harrilal (2009) examined the total erosion process of transport of soil particles detached by raindrop which is commonly referred as interrill erosion (Levy et al., 2001). Piarco sandy loam had the largest quantity of mean soil loss and this has been consistent in the with these two recent studies. Although this soil had the least runoff as the rainfall duration increased (Tables 3 and 4), its low percentage clay content (18.1%, Table 1) decreased the soil strength (Table 6), thus decreasing the soil's ability to increase the cohesiveness of the particles. The larger size of the sandy loam soil led to greater presence of large pores which enhanced infiltration. Results show that this led to lower surface runoff. However, decreased soil cohesiveness, the presence of more loose detached sand particles ensured that the soil had greater soil loss than the other soils despite its maintenance of high infiltration and low

With the 46.3% clay content of the Talparo clay soil (Table 1), the soil cohesiveness and soil strength (Table 6) was the greatest as was measured by the soil penetration test. However, due to the low infiltration and high runoff rates recorded for this soil, the Talparo soil still had more soil loss than the Maracas clay loam soil. Although there was little raindrop detachment, due to the quantity of clay in the soils composition, the Talparo clay experienced the lowest infiltration and greatest amount of surface runoff of the three soils (Tables 3 and 4). This quantity of surface runoff was able to produce soil erosion, and as the rainfall duration increased, so too did the runoff and also the quantity of erosion. However, its high clay composition and high soil strength ensured that there was less erosion than the Piarco sandy loam. The Maracas clay loam had the least soil loss. This was mainly its evenly balanced composition of sand, silt and clay (Table 1). The Maracas clay loam had 30.6% clay content which was enough to produce good cohesive nature and soil strength for the particles so as to minimize splash erosion and easy detachment. The sand and silt composition allowed the soil to have steady infiltration throughout the testing period and leading to runoff which was closer to that recorded for the sandy loam soil (Table 4). These
