Conservation tillage implements and systems for smallholder farmers in semi-arid Ethiopia

Abstract

Smallholder farmers in Ethiopia practice traditional tillage systems using an ard plow called Maresha. Traditional tillage systems that involve repeated cultivations with the Maresha plow have caused land degradation (a.o. formation of a plow pan) and poor utilization of rainwater that led to low crop productivity. Experience in other countries has shown that conservation tillage systems could improve utilization of rain water through increased infiltration. However, the implements used for conservation tillage in other countries were found to be too heavy and too expensive for smallholder farmers in Ethiopia. On the other hand, lighter and low cost implements have been developed in Ethiopia as modifications to the Maresha plow. These implements are the Subsoiler, the Tie-ridger, and the Sweep. Field tests were carried out to evaluate the modified implements and a rip plant type of conservation tillage systems using the modified implements. The results showed that the Subsoiler reached a depth of approx. 24 and 27 cm after 1 resp. 2 passes through the furrow made by the Maresha, and thus was capable of disrupting the plow pan. Compared to the Maresha plow and the inverted broad bed maker (BBM), the Tie-ridger required less draft power (79 kg vs. 96 for the Maresha and 103 for the BBM) and lower lifting force (−43%) while forming furrows with larger (+36 resp. +15%) cross-sectional areas. The Sweep enabled deeper root growth of tef (Eragrostis tef (Zucc.)) apart from accomplishing sowing operations faster (+50%). It is concluded that the newly developed implements are suitable to undertake conservation tillage under smallholder farming systems in the semi-arid regions of Ethiopia. The rip-plant type of conservation tillage systems, however, was not found to be viable for maize (Zea mays) production under the study conditions in which loss of soil moisture through evaporation is high. Both grain and biomass yields were highest in the conventional systems, although differences were statistically not significant. On the other hand, a reduced tillage system tested on tef resulted in higher grain yields as compared to conventional tillage.

Introduction

Ethiopia is located in the Horn of Africa between 3° and 18°N and 33° and 48°E. Its population is currently estimated at 60 million. Agriculture is the mainstay of the country's economy with 60% of GDP coming from this sector. It is a means of livelihood for about 85% of the total population. The main power sources in agriculture are humans and animals. Over 90% of the total agricultural production comes from 5.5 million farmers employing 5 million oxen and cultivating 95% of the arable land (Pathak, 1987).

The semi-arid regions in Ethiopia (Fig. 1) cover a total area of 301,500 km². This area represents the crop production zone suffering from a serious moisture stress (Engida, 2000). It is in these areas that food insecurity and famine has often been reported (IGAD and FAO, 1995). Although drought is the major reason causing famine in Ethiopia, low level of agricultural productivity due to poor management of the available resources, particularly water, due to poor rainfall partitioning (high run off, high evaporation and low infiltration), is a very important factor that has rendered the country even more vulnerable to drought.

The traditional tillage implement in Ethiopia, the Maresha plow, and the related tillage system that requires repeated cultivation, have caused land degradation (poor soil structure, low fertility and loss of soil through erosion) (Bezuayehu et al., 2002), delayed planting and hard work to both draft animals and human beings (Rockstrom et al., 2001). Poor soil structure has resulted in poor rainwater retention and infiltration (Rockstrom and Valentin, 1997, Hoogmoed, 1999) while delayed planting has shortened the length of the growing period available for the crop (Rowland, 1993). The high draught power required for tillage has forced farmers to keep a large number of cattle for breeding purposes. Such an overstocking of cattle has in turn led to land degradation (Biamah and Rockstrom, 2000, Jonsson et al., 2000).

Farmers in Ethiopia have used the Maresha plow (Fig. 2) for thousands of years (Goe, 1987, Gebregziabher et al., 2006). It is very simple, light in weight, cheap, and locally made. However, as a conventional tillage implement, the Maresha plow has got several drawbacks which arise mainly from the fact that the plow forms a V-shaped furrow and results in incomplete turnover (Sime, 1986). These drawbacks are:

• Because of the incomplete turnover of the furrows, farmers have to do repeated tillage in order to produce a fine seedbed especially for tef. As a result, the soil is excessively pulverized resulting in a poor structure leading to crust formation.

• Because of the V-shaped furrow formed by the Maresha plow it is necessary that every two consecutive tillage operations are oriented perpendicular to each other. Thus, in inclined fields one of the two plowing operations fall along or nearly along the slope. The furrows encourage runoff when they are laid along the slope (Edwards et al., 1993, Basic et al., 2001). This is a very serious problem in Ethiopia because the country is very hilly resulting in large amounts of soil and water loss due to erosion.

• Because of repeated tillage at shallow depth plow pans are formed which hinder water infiltration (Whiteman, 1979) and root growth (Rowland, 1993, Willcocks, 1984).

• The V-shaped furrow exposes a larger surface area of the soil to the atmosphere. Rough surfaces appearing during tillage operations enhance gas exchanges CO₂ (Reicosky, 2001) resulting in losses of organic carbon. Moreover, evaporation losses are higher due to larger surface area exposure.

Research to improve the Maresha plow began as early as 1939 when the Italians introduced the animal drawn mould board plow (Goe, 1987). FAO (Food and Agriculture Organization) conducted a series of on-farm trials on implements in the 1950s while the Alemaya and the Jimma Agricultural Colleges made efforts to improve the traditional tillage implement in the early 1960s. In 1968, the Chilalo Agricultural Development Unit started research on several types of tillage implements while the Institute of Agricultural Research began activities on improving the traditional implements in 1974. However, none of these efforts were successful in developing prototypes acceptable by Ethiopian farmers (Goe, 1987). The major reasons behind the reluctance of farmers to adopt the newly introduced implements were the fact that they were too heavy and expensive.

Recently, the following implements have been developed as attachments to or modifications of the Maresha plow aimed at undertaking field operations related to conservation tillage (Temesgen, 2000).

• The Subsoiler. Conventional tillage systems often cause the formation of plow pans or hard pans that restrict infiltration and root growth. One of the objectives of conservation tillage practices is to break the hard pan. The Subsoiler was made by replacing the tip of the Maresha plow by a narrow metallic part and the wooden boards by a pair of iron rods.

• The Sweep. The Sweep was made by replacing the wooden boards of the Maresha plow by a pair of rods and a 55 cm wide steel blade that moves horizontally through the soil. The main purpose of the Sweep is to improve timeliness of operations, and secondly, the Sweep is designed to mix fertilizer with the soil before tef sowing. It operates shallowly thereby reducing draft power requirements and increasing speed of operation. As it has got a larger width of operation, more area is covered per unit of time. Traditionally, farmers broadcast fertilizer on the surface and do not mix it with the soil. The reason is that if they mix it using the Maresha plow the fertilizer will be buried too deep for the shallow-rooted tef crop. Leaving fertilizer on the surface causes losses due to volatilizations and sheet erosion. Moreover, the roots of the tef crop are forced to concentrate at the surface where the fertilizer is placed. The former is particularly important when there is a dry spell during which the upper layer dries out with the moist layer progressively moving down the soil profile. It is hypothesized that if the Sweep is used to mix the fertilizer with the soil the roots will grow deeper in search of the nutrients thereby enabling the plant to use more water from the soil profile.

• The Tie-ridger. In semi-arid regions of Ethiopia, rainfall is erratic, with high intensity rainfall followed by long dry spells. Water is lost through run off and the soil dries out quickly during the dry spells. Tied ridges are a series of basins formed in the field by tying furrows at certain intervals (Temesgen, 2000). The Tie-ridger was made by attaching a blade vertically just behind the plow point that can be lifted by the operator (thus tipping the plow). The blade is designed to make wider furrows with reduced draft power requirement and lower lifting forces.

• The inverted BBM (broad bed maker). The broad bed maker that was initially developed to make broad bed and furrow for draining excess water in highland vertisols was later modified such that it can be used as a Tie-ridger (Wondimu et al., 1998). The inverted BBM was made by attaching the wings of the BBM on both sides of the Maresha plow such that it forms a moldboard-type ridger.

The rip-plant type of conservation tillage uses appropriate animal-drawn equipment such as Subsoilers or rippers. These systems have been extensively tested for smallholder farmers in Africa (Ahenkorah et al., 1995, Chen and Li, 1998, Steiner, 1998, Biamah and Rockstrom, 2000, Freitas, 2000, Wanders and Stevens, 2000). The system involves making furrows at 75 cm spacing using a ripper and leaving the rest undisturbed. Subsoiling is also made in these lines. Finally, planting is carried out in the same furrows. The system has been found effective and is being popularized among smallholder farmers in much of the Southern and Eastern African countries. The implements were developed as attachments to the moldboard plow frames that are too heavy and unaffordable by smallholder farmers in Ethiopia (Temesgen, 2000, Goe, 1987).

An alternative conservation tillage system was designed using the Maresha modified implements. This would be appropriate for row planted crops such as maize. However, for broadcasted crops such as tef there is a need to introduce a reduced tillage system in which the field will be plowed once.

This paper presents the results of an evaluation of the Maresha modified implements and conservation tillage systems on maize and tef in order to:

• Evaluate the field performance of the newly developed implements with particular emphasis on their ability in reducing the time and energy required for the particular operation and in making more water available to the crop under rain fed agriculture in sem-arid regions.

• Evaluate the agronomic performances of the rip-plant type conservation tillage system and a reduced tillage system for row planted and broadcasted crops, respectively.