**1. Introduction**

178 Soil Erosion Studies

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Soil erosion, and its associated impacts, is a big environmental problem, globally. The resulting costs of this phenomenon are tremendous and originate from both on-site and ofsite effects of erosion (Morgan, 2005). On-site effects are particularly important on agricultural lands. The outcome includes loss of soil fertility and productivity, breakdown in soil structure, and at times loss of life and property. This decline in fertility leads to increased costly fertilizer use, affects food production and food security and substantial declines in land values. Off-site problems generally result in downstream or downwind sedimentation. There is also the issue of pollution transfer from place to place.

It is thus very important that new methods and practices for reducing and/or controlling erosion be developed and existing ones improved so as to combat this very important problem. There is also the need to encourage the use of existing agri-environmental management methods like the use of geotextiles and soil conditioners. Basically, all strategies for soil conservation include the following: providing a barrier against raindrop impact, increasing soil aggregate stability, increasing infiltration capacity of the soil to reduce runoff and/or increasing surface roughness to reduce velocity of runoff and wind (Morgan, 2005).

Peat is sometimes used as a source of organic matter for the soil. In Trinidad, peat is particularly used in nurseries, because unlike other organic materials like FYM, its incorporation is not accompanied by weeds infestation. Peat increases soil fertility and improves physical properties like saturated hydraulic conductivity (Ohu et al., 1985) and available water and reduces bulk density (Lebeau et al., 2003; Ekwue and Harrilal, 2010).

Soil erosion by water consists of two basic processes: splash detachment and transport by raindrops and runoff. Splash erosion is the first step in the soil erosion process and control measures are best targeted at reducing it. Ekwue (1990, 1992) found that splash detachment by raindrops declined with increasing peat content of soils and noted that the relationship was negatively exponential over a range of organic matter content (1.50 – 18.23%). Peat was found to act as mulch and thereby protecting the soil surface from the direct impact of raindrops. Ekwue et al. (2009) further found that peat decreased soil transport by runoff or overland flow (wash erosion). However, it was not clear why peat

Soil Loss-Rainfall Duration Relations as Affected

oven dried to determine the mass of soil eroded.

Fig. 1. The soil bed of the erosion facility

by Peat Content, Soil Type and Compaction Effort 181

The apparatus measures erosion on surfaces with slopes varying from 0% to 30%. The soil tray has a flexible drainage hose added to the bottom end throughout the length of it. Gravel was placed at the bottom of the soil tray to a depth of 8 cm before putting the soil to be tested, such that water that infiltrated through the soil first passed through the layer of gravel, which acted as a filter, and ensured that clean water flowed down the drain preventing the siltation of the drain pipes. During testing, the eroded soil and overflow water (runoff) flowed into the soil collection pan. Here soil settled under its own weight. From this compartment, the water flowed through a drainpipe and into a drain where the runoff was measured. Sediments were collected from the collection tray after the tests and

For each test, soil was added to the soil tray to a depth of 2 cm. This is the depth of soil that is normally involved in the soil erosion process. Soil was then compacted at three levels (100 kPa, 150 kPa and 185 kPa). The three compaction levels were obtained using a 3.6 kg roller 2, 3, and 4 times each followed by a 5.8 kg roller 3, 4 and 5 times respectively. The aim was to produce a compacted soil similar to field conditions and to determine the effect of these levels of compaction on soil erosion. Bulk density and penetration resistance achieved after soil preparation were measured using a hand pushed spring-type Proctor penetrometer (ASTM, 1985). Erosion by simulated rainfall was assessed using a factorial experiment involving the three soils with the three peat contents, and exposed to four rainfall durations (5, 10, 20 and 30 min) with two replications giving a total of 216 tests. The slope gradient was fixed at 9% which is prevalent in agricultural soils in Trinidad (Gumbs, 1987). Analysis of variance of soil erosion values was performed using the MINITAB computer software.

reduced soil transport since it is known to reduce inter-aggregate stability and soil strength which affects the soil erosion process. Ekwue and Harrilal (2010) followed it up by studying the effect of peat on wash erosion by raindrop impact and observed that peat decreased wash erosion by reducing soil bulk density, increasing infiltration rates and decreasing runoff. The effect of peat incorporation on the overall soil erosion process is therefore now clearly understood. Soil erosion by raindrops is also known to be affected by rainfall duration but it is not clear how this relationship is affected by other parameters that affect the soil erosion process including peat content, soil compaction and soil type. This paper reports the results of an interaction experiment set up to examine the relative effects of peat content, soil type, rainfall duration and compaction efforts on raindrop erosion. The aim is to further increase the general understanding of how peat affects the soil erosion process.
