Research
An investigation into Malawi’s compacted soil ‘hoe pan’ (1999)
Overview
The declining productive capacity of Malawi’s soil is a cause of great concern. This decline is due to widespread soil degradation in the country, which Malawi’s State of the Environment Report rated as Malawi’s most severe environmental problem. Significant decreases in fertilised maize yields, and respective decreases in crops’ response to fertiliser, evidence the soil’s declining productivity. There are multiple factors responsible for this problem, including:
One of the principal approaches taken to address the declining soil productivity is the increased use of hybrid maize and chemical fertilisers, but this approach does not take into account the fact that there are multiple factors – beyond seed type and insufficient nitrogen in the soil – responsible for soil’s declining productivity. Often overlooked is the presence of a compacted layer of soil beneath the topmost soil layer referred to as the “hoe pan” (and later, the “hardpan”), which was the focus of this study.
The compacted hoe pan is a man-made phenomenon resulting from tillage practices used in conventional ridge farming. Conventional ridge farming was widely promoted across Malawi for decades, becoming the predominant agricultural method. The compaction is exacerbated by pressure from human footfall as farmers walk between the ridges to carry out farming activities. The hoe pan restricts the ability for rainwater and roots to penetrate deeply into the land with the following consequences:
The declining productive capacity of Malawi’s soil is a cause of great concern. This decline is due to widespread soil degradation in the country, which Malawi’s State of the Environment Report rated as Malawi’s most severe environmental problem. Significant decreases in fertilised maize yields, and respective decreases in crops’ response to fertiliser, evidence the soil’s declining productivity. There are multiple factors responsible for this problem, including:
- low soil nutrient levels
- low levels of organic matter in the soil
- heightened moisture stress (low/erratic rainfall combined with poor moisture retention in the soil)
- increased threat from the parasitic weed Striga
- low quality maize seed due to loss of traditional/local maize varieties
One of the principal approaches taken to address the declining soil productivity is the increased use of hybrid maize and chemical fertilisers, but this approach does not take into account the fact that there are multiple factors – beyond seed type and insufficient nitrogen in the soil – responsible for soil’s declining productivity. Often overlooked is the presence of a compacted layer of soil beneath the topmost soil layer referred to as the “hoe pan” (and later, the “hardpan”), which was the focus of this study.
The compacted hoe pan is a man-made phenomenon resulting from tillage practices used in conventional ridge farming. Conventional ridge farming was widely promoted across Malawi for decades, becoming the predominant agricultural method. The compaction is exacerbated by pressure from human footfall as farmers walk between the ridges to carry out farming activities. The hoe pan restricts the ability for rainwater and roots to penetrate deeply into the land with the following consequences:
Problem |
Restricted rainwater infiltration |
Restricted root development |
Consequences |
|
|
Practical implications
In seeking to address the declining productivity of Malawi's soil, the first and most crucial step is to break the hoe pan. This step will improve the capacity for roots and rainwater to infiltrate deeply into the soil. Crops will be able to develop deeper roots that can access greater nutrient and moisture resources, making them more resilient to periods of low or erratic rainfall. Improved rainwater infiltration will also reduce surface runoff and related soil erosion. To avoid re-compaction of the soil, it is also advised that farmers move away from conventional ridge farming and the associated tillage practices, which were the initial cause of the hoe pan’s formation.
The study also made other suggestions for how smallholder farmers could improve their soil’s productivity to achieve heightened crop yields. One suggestion was to create ‘double dug beds’, where farmers dig out soil to twice the typical cultivation depth and then re-fill this space with a combination of soil and compost. The compost increases the soil’s nutrients and its ability to retain moisture while facilitating deeper root growth, all of which contribute to enhanced soil productivity. Authors also advised the use of crop rotation and/or intercropping, noting pigeon pea to be an especially promising option in Malawi.
Finally, the authors identified necessary areas for further work. First, they called for further studies to identify the full extent and intensity of the hoe pan problem (e.g., what types of soil are more affected, where these soils are located, what types of cultivation and land management practices can cause the formation of the hoe pan). Authors also highlighted the need to develop land management (including agricultural) practices that would avoid hoe pan formation and break hoe pans that currently exist. Importantly, these practices must be accessible to resource-poor farmers.
Read the full article here.
Reference: Douglas, M.G., Mughogho, S.K., Saka, A.R., Shaxson, T.F. and Evers, G. (1999) ‘Malawi: An investigation into the presence of a cultivation hoe pan under smallholder farming conditions.’ TCI Occasional Paper No. 10, FAO Investment Centre.
In seeking to address the declining productivity of Malawi's soil, the first and most crucial step is to break the hoe pan. This step will improve the capacity for roots and rainwater to infiltrate deeply into the soil. Crops will be able to develop deeper roots that can access greater nutrient and moisture resources, making them more resilient to periods of low or erratic rainfall. Improved rainwater infiltration will also reduce surface runoff and related soil erosion. To avoid re-compaction of the soil, it is also advised that farmers move away from conventional ridge farming and the associated tillage practices, which were the initial cause of the hoe pan’s formation.
The study also made other suggestions for how smallholder farmers could improve their soil’s productivity to achieve heightened crop yields. One suggestion was to create ‘double dug beds’, where farmers dig out soil to twice the typical cultivation depth and then re-fill this space with a combination of soil and compost. The compost increases the soil’s nutrients and its ability to retain moisture while facilitating deeper root growth, all of which contribute to enhanced soil productivity. Authors also advised the use of crop rotation and/or intercropping, noting pigeon pea to be an especially promising option in Malawi.
Finally, the authors identified necessary areas for further work. First, they called for further studies to identify the full extent and intensity of the hoe pan problem (e.g., what types of soil are more affected, where these soils are located, what types of cultivation and land management practices can cause the formation of the hoe pan). Authors also highlighted the need to develop land management (including agricultural) practices that would avoid hoe pan formation and break hoe pans that currently exist. Importantly, these practices must be accessible to resource-poor farmers.
Read the full article here.
Reference: Douglas, M.G., Mughogho, S.K., Saka, A.R., Shaxson, T.F. and Evers, G. (1999) ‘Malawi: An investigation into the presence of a cultivation hoe pan under smallholder farming conditions.’ TCI Occasional Paper No. 10, FAO Investment Centre.