Agronomic Practices and Conservation in Ethiopia

Introduction

Land degradation is a major problem that requires urgent intervention measures. This is especially true in the poorest countries, where agricultural production is crucial to development, and the livelihoods of the majority of the population depend on the primary sector (Barbier & Bishop, 1995). Land degradation, in the form of soil erosion and nutrient depletion, is a major threatening factor for aggravating food insecurity and exacerbate the sustainability of agricultural production in Ethiopia1. During 1981 and 2008, the total land degraded in the country is estimated to be 297,000 km2.

Annually, the mean rates of soil loss associated with croplands have been about 42 t haG12, 3. Poor watershed management, population growth, and inappropriate farming practices have contributed to a lion’s share of the losses caused. Besides, poverty with a rapid increase in the human population combines with land degradation poses a serious threat to the national economy and household food security4.

Furthermore, soil erosion hampers agricultural productivity through deteriorating soil quality (loss of organic matter and mineral contents) by means of excessive surface runoff5-7.

As far as surface runoff is concerned, the trans-boundary Rivers that originated from Ethiopian highlands and carries about 1.3 billion tyrG1 of sediments to neighboring countries8. In addition, soil erosion also causes the change in physical properties of the soil such as texture, infiltration rate, bulk density, water holding capacity and root depth. However, in Ethiopia for the past decades, an attempt was made to undertake mitigation measures on soil erosion problems using different approaches for the sustain ability of crop production9, 10.

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Besides, watershed management approach has been applied in the country to reduce environmental degradation and to enhance agricultural productivity, which supports sustainable livelihoods security of the households. In this regard, the use of soil and water conservation practices in association with crop production is determined by the combined effect of biophysical and socio-economic factors9.

In Ethiopia, the problem of land degradation especially soil erosion and depletion of nutrients is a critical environmental crisis (FARM-Africa, 2005). Following this, the natural resource has become increasingly depleting, rapid land conversion takes place and resulting unsustainable land management and land degradation (Zeleke, 2010). The question of soil conservation becomes most crucial because the soil is very easily eroded within no time. At the same time, it should be remembered that it takes hundreds of years to form one-centimeter thick layer of soil (Morgan, 2005). Most of the cultivated lands are slopping and require one or more types of soil and water conservation measures. The topography and agro-climatic conditions are also varying; that one should have the ability to discern what type of soil and water conservation measures a particular land area requires (FAO, 1984). Most of the cultivated land needs application of long-term soil and water conservation measures followed by reorganization of land use pattern efficiently including soil moisture conservation, improvement of soil productivity and cropping and farming systems (Josh et al., 1999).

There are different ways of conserving soil and water. Generally, they are mechanical, biological and agronomic soil and water conservation (Tidemann, 1998; Morgan, 2005; FAO, 1984). The soil conservation measures adopted in the cropping systems and practices is called agronomic measures (Morgan, 2005). Agronomic conservation measures function by reducing the impact of raindrops through interception and thus reducing soil erosion and increasing infiltration rates, and also reducing surface runoff and soil erosion (Tidemann,1996).There are a number of the agronomic measures of soil and water conservation. However, not all practices are suitable or practical in all the places under all the agronomic practices. Therefore, the aim of this paper is to review commonly applied agronomic soil and water conservation practices and its’ role in soil and water conservation for climate change adaptation.

The concept of agronomic measure

There are numerous definitions and concepts of agronomic practices available in the literature. The agronomic measures are referred by the practices of growing vegetables on mild sloppy lands to cover them and to control the erosion from there in living vegetation above the soil surface dissipates the crave the power of agents either they are water or wind (Tidemann, 1998). In case of water erosion, it affects by several ways such as by enhancing infiltration rate and thereby reducing runoff velocity to scour the soil particles screening the eroded particles to reach them into the channels or reservoirs; by dissipating the kinetic energy of falling raindrops and thus reducing the splash erosion (Morgan, 2005).

Agronomic conservation measures function by:

• reducing the impact of raindrops through interception and thus reducing soil erosion and
• increasing infiltration rates and thereby reducing surface runoff and soil erosion.

These measures can be applied together with physical or biological soil and water conservation measures. In some systems, they may be more effective than structural measures. Furthermore, it is the cheapest way of soil and water conservation. The significance of land use practices becomes apparent in a comparison made by Tidemann 1996: ‘According to FAO (1984), agronomic measures is that vegetation is used, either alive or dead, in sufficient quantities to shield the soil surface from the direct impact of raindrops and to create a rough surface which will physically impede run-off and slow it down to non-erosive velocities. The role of agronomic measures in achieving of soil & water conservation has immense importance. It is important to understand and disseminate the different soil management practices used to cultivate the soil and grow the crops (Lynden & Lane, 2004).

Types of Agronomic Practices

The major agronomic soil and water conservations practices in Ethiopia are – Strip cropping, mixed cropping, intercropping, fallowing, mulching, contour plowing, crop rotation, conservation tillage, and agroforestry (Mati, 2005)

1. Improved Fallow Systems (IFS): Arable lands are planted with food crops for some years and then the land is fallowed for some time to allow the soil to rejuvenate (Meine & Bruno, 2000). To shorten the fallow period, the area can be seed with leguminous trees. Once the soil has been rejuvenating, the trees are clear for crops. This can be considered as an improved version of the traditional shifting cultivation (Burgers et al., 2005).

2. Strip Cropping: It is a kind of agronomical practice, in which ordinary crops are planet or grown in form of relatively narrow strips across the land slope. These strips are so arranged, that strips of close-growing and erosion resistance crops should always separate the strips crops. Strip cropping checks the surface runoff and forces them to infiltrate into the soil, which facilitates the concentration of rainwater (Morgan, 2005).

3. Natural Vegetative Strips (NVS): When land is plow along contour lines, certain strips of 40-50 cm wide are left un-plow, across the field on the contour (Garrity et al., 2004). The natural vegetation of the strips filters the eroded soils, slows down the rate of water flow, and enhances water infiltration, making them very effective for soil and water conservation. Researchers found that these natural vegetative contour strips have many desirable qualities (Garrity et al., 2004).

5. Contour Tillage: It refers to all the tillage practices, mechanical treatments like planting, tillage, and intercultural performed nearly on the contour of the area applied across the land slope (Meine & Bruno, 2000). It involves plowing, planting, and weeding along the contour, i.e., across the slope rather than up and down (Morgan, 2005). It also conserves soil, and due to increased time of concentration, more rainwater seeps through the soil profile to recharge groundwater. Summer plowing leaves the soil highly absorbent of initial rains (Deborah, 2003).

6. Mixed/Intercropping: Intercropping is the cultivation of two or more crops at the same time in the same field (Meine & Bruno, 2000; Andersen, 2005). A wide range of crops can be used for intercropping. Mixed cropping of different crops along with the main crops, such as millets and different legumes, is insurance against climate change. The different root systems of mixed crop feed at different depths of the soil. Moreover, mixing cropping provides small quantities of a grain of different kinds of home consumption at different times (Morgan, 2005)

7. Mulching: Mulches are ground covers that prevent the soil from being washed away, reduce evaporation, increase infiltration, and control the growth of unwanted weeds (Deborah, 2003). Mulch can be organic crop residue, pebbles, or materials such as polythene sheets. Mulching prevents the formation of the hard crust after each rain. Organic mulches add plant nutrients to the soil upon decomposition.

8. Conservation Tillage: Is any method of soil cultivation that leaves the previous year’s crop residue on fields before and after planting the next crop to reduce soil erosion and runoff, as well as other benefits such as carbon sequestration. The method tries to reduce labor in land preparation through tillage systems that promote soil fertility and soil water conservation. Conservation tillage applying four main principles:

1. zero or minimum soil turning,
2. permanent soil cover,
3. stubble mulch tillage,
4. crop selection and rotations (Biamah et al., 2000).

9. Agroforestry (AF): It refers to a system of land uses in that there are different trees or shrubs are grown in association with different agricultural crops, pastures, or livestock. In relation to this, one of the most important features of AF is that there are both ecological and economic interactions between the trees and other components (Young, 1989) such nature of the integration of trees and shrubs in the land-use system can be either a spatial arrangement, or in a time sequence, e.g. trees growing in a field at the same time as a crop, or shrubs grew on a fallow for the restoration of soil fertility. This is the most common practice in Sidam and Gedio Zone, Southern Ethiopia.

10. Crop Rotation: It involves alternating cereal crops with a legume, pulse, or oilseed crops. This type of rotation produces differing amounts and types of residue thus make crop residue and trash management easier. Therefore, a rotation is the key to success in reduced tillage systems, reduces soil erosion, and then climate change adaptation (Ailincai et al., 2009).

The Role of Agronomic Practices on Soil and Water Conservation (SWC)

As it is known, soil and water conservation is not only to indicate keeping the soil in its place from erosion but also to maintain the soil fertility (Morgan, 2005; Young, 1989). For doing so, SWC requires control of erosion, maintenance of organic matter and soil physical properties, maintenance of nutrients, and avoidance of toxicity (Young, 1989). Therefore, in soil and water conservation point of view agronomic practices provide a protective role. This is by its prevention of soil from loss by its plant canopy, litter effect, and reduction of the velocity of runoff mechanically by runoff barrier function (Young, 1989; Kilewe et al., 1988). This can be viewed in its interception effect, i.e. the plant canopies, litter, and mulching intercept rain by decreasing the amount, intensity, and the spatial distribution of the precipitation reaching the soil surface (Kilewe et al., 1988). This protects the soil surface from the direct impact of raindrops, which can cause a splash and sheet erosion, a breakdown of the soil structure, sealing of the surface, and reduction of infiltration rates (Morgan, 2005; Young, 1989).

Agronomic practice improves the soil physical conditions by the maintenance of soil properties (structure, porosity, moisture retention capacity, and permeability) and through a combination of maintenance of organic matter with the effects of roots (breaking up of compact layers by roots). In addition, there is a modification of extremes of soil temperature through a combination of shading by canopy and litter cover (Young, 1989). In the parkland practice, Faidherbia albida is one example of an important tree that increases soil-improvement including nutrient cycling and crop yield in Malawi and in Ethiopia (Buck et al., 2007).