Physical characteristics

Good structure: Fertile soil has a well-balanced mix of sand, silt, and clay particles, allowing for good water infiltration, aeration, and root growth.

Optimal texture: The ideal soil texture is a mix of 40-60% sand, 20-40% silt, and 10-20% clay.

Adequate porosity: Fertile soil has a good balance of pores, allowing for water and air to penetrate and roots to grow.

Chemical characteristics

Optimal pH: Fertile soil typically has a slightly acidic to neutral pH, ranging from 6.0 to 7.0.

Adequate nutrient levels: Fertile soil contains sufficient levels of essential nutrients like nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur.

Good cation exchange capacity (CEC): Fertile soil has a high CEC, allowing it to retain and exchange nutrients with plants.

Biological characteristics

High microbial activity: Fertile soil is teeming with beneficial microorganisms like bacteria, fungi, and protozoa, which help break down organic matter and make nutrients available to plants.

Presence of earthworms and other soil fauna: Fertile soil is home to a diverse range of soil fauna, including earthworms, insects, and micro arthropods, which help mix and aerate the soil.

Good organic matter content: Fertile soil contains a sufficient amount of organic matter, such as humus, compost, or crop residues, which helps maintain soil structure, fertility, and overall health.

Other Characteristics

Good water-holding capacity: Fertile soil can retain and release water as needed, reducing the risk of drought and waterlogging.

Resistance to erosion: Fertile soil is less prone to erosion, as it has a stable structure and good vegetative cover.

Supports biodiversity: Fertile soil supports a diverse range of plant and animal species, promoting ecosystem services and overall ecosystem health.

Soil fertility is declining in Kijumba in Mubende District, Uganda. The picture below shows maize growing in land that has no rest and hardly any fertilisers are applied.

The factors that contribute to this soil decline include various human activities and natural factors. Here are some reasons contributing to this decline:

Intensive farming: Monoculture farming practices involving growing maize and beans almost every year, without adequate crop rotation continue to contribute to soil degradation and nutrient depletion.

Soil Erosion: There are hardly any measures to reduce soil erosion. As a result, soil erosion due to wind and rainwater, has led to the loss of fertile topsoil and nutrient-rich sediments.

Nutrient Depletion: Every rainy season, farmers hardly give their land break. They continuously grow maize or beans without adequate nutrient replenishment and this has led to soil nutrient depletion.

Climate Change: Kijumba is located in cattle corridor area that scarcely receive adequate amount of rain. In addition, the rising temperatures, changing precipitation patterns, and increased frequency of extreme weather events probably has contributed to alteration in soil processes and reduce fertility.

Soil Pollution: The farmers utilse herbicides to reduce weed before and during crop growth. This continues to contaminate soil as these agricultural chemicals can harm soil biota and reduce fertility. The use of herbicides can have both short-term and long-term effects on soil fertility:

Short-term effects

Soil microbiome disruption: Herbicides can alter the soil microbiome, reducing the populations of beneficial microorganisms that play a crucial role in decomposing organic matter, fixing nitrogen, and making minerals readily available for the plant uptake.

Nutrient imbalance: Herbicides are said to interfere with nutrient cycling, leading to an imbalance of essential nutrients like nitrogen, phosphorus, and potassium that are critical for plant and crop growth.

Soil structure alteration: Some herbicides can alter soil structure, reducing its water-holding capacity, aeration, and root penetration.

Long-term effects

Soil degradation: Repeated use of herbicides has led to soil degradation, reducing its fertility and productivity over time.

Nutrient depletion: Herbicides deplete soil nutrients, particularly nitrogen and phosphorus, which are essential for plant growth.

Soil erosion: Herbicides contribute to increasing soil erosion through reducing vegetation cover, altering soil structure, and increasing runoff.

Contamination of groundwater: Herbicides are likely to contaminate groundwater, posing a risk to human health and the environment.

Herbicide-specific effects

Glyphosate (Roundup): Glyphosate can alter soil microbiome, reducing nutrient availability, and increase soil erosion.

Atrazine: Atrazine can contaminate groundwater, reduce soil fertility, and alter soil microbiome.

2,4-D: 2,4-D can reduce soil fertility, alter soil microbiome, and increase soil erosion.

Steps farmers can take to reverse declining soil fertility

Short-term measures (0-5 years)

Soil testing: The district local government can make the soil testing service available to enable farmers carry out regular soil test to determine nutrient levels, pH, and contaminants and use the findings to make corrective measures.

Crop rotation and intercropping: The Mubende District Local government extension workers should mobilise farmers to implement crop rotation and intercropping to promote soil biodiversity and nutrient cycling.

Organic amendments: These extension workers can train the farmers to locally make and apply organic amendments like compost, manure, or green manure to replenish soil nutrients.

Conservation tillage: The farmers should be trained and mobilized to adopt conservation tillage practices to reduce soil disturbance and erosion.

Cover cropping: The farmers should be mobilized to plant cover crops to protect soil, promote soil biota, and add organic matter.

Medium-term measures (5-20 years)

Agroforestry: In addition, the farmers can be trained to Integrate trees into agricultural landscapes to promote soil health, biodiversity, and ecosystem services.

Perennial cropping: Establish perennial crops like fruit trees, nut trees, or perennial grasses to reduce soil disturbance and promote soil carbon reduction.

Soil conservation structures: The farmers should be trained and mobilized to construct soil conservation structures like terraces, contour bunds, or check dams to reduce soil erosion.

Integrated nutrient management: Implement integrated nutrient management practices that combine organic and inorganic nutrient sources to optimize soil fertility.

Soil biota management: Promote soil biota through practices like reduced tillage, cover cropping, and organic amendments to enhance soil ecosystem services.

Long-term measures (20-50 years)

Ecological restoration: The district local government can work with the community to restore degraded lands through ecological restoration practices that promote native vegetation, soil biota, and ecosystem services.

Sustainable agriculture: Train and mobilise farmers to adopt sustainable agriculture practices that prioritize soil health, biodiversity, and ecosystem services, such as regenerative agriculture or permaculture.

Implement practices that promote revival of soil health, such as no-till or reduced-till farming, cover cropping, and incorporating organic amendments.

Agro ecology: Promote agro ecology practices that prioritize soil health, biodiversity, and ecosystem services, and reduce reliance on external inputs.

Policy and institutional support: The District local government can enforce the policies that support sustainable soil management, provide incentives for farmers to adopt sustainable practices, and promote soil conservation and restoration.

Mitigating the effects of herbicides on soil fertility:

Integrated pest management (IPM): Train and mobilise farmers to implement IPM strategies that combine physical, cultural, biological, and chemical controls to minimize herbicide use.

Crop rotation and intercropping: Taint and mobilise farmers to practice crop rotation and intercropping to promote soil biodiversity, reduce soil erosion, and increase nutrient availability.

Organic amendments: Promote the use of organic amendments like compost, manure, or green manure to replenish soil nutrients and promote soil biota.

Conservation tillage: Adopt conservation tillage practices to reduce soil disturbance, promote soil biota, and increase soil organic matter.

Soil testing and monitoring: The district local government should institutionalize regular test and monitor soil to determine nutrient levels, pH, and contaminants, and adjust management practices accordingly.

Promote soil conservation techniques that include the following:

Contour planting: In hilly areas, planting crops along contours helps to reduce erosion, conserve water, and promote soil fertility.

Terracing: Creating terraces helps to reduce erosion, conserve water, and promote soil fertility.

Swales: Creating swales (shallow ditches) helps to harvest and conserve rainwater, reducing erosion and promoting soil fertility.

Promote soil biodiversity enhancement techniques

Agroforestry: Integrating trees into agricultural landscapes helps to promote biodiversity, improve soil fertility, and increase ecosystem services.

Pollinator support: Planting pollinator-friendly crops helps to attract beneficial insects, promote biodiversity, and improve soil fertility.

Soil biota support: Using techniques like compost tea and worm casting helps to support beneficial microorganisms, promote soil fertility, and improve ecosystem services.

Climate-smart agriculture: The government should mobilise resources to support farmers to adopt climate-smart farming practices like drought-tolerant crops, irrigation during the dry season, agroforestry, and conservation agriculture to improve soil fertility and resilience.

Policy and institutional support

Soil fertility policy: Review and implement the existing Government of Uganda policies that promote soil fertility management and conservation.

Extension services: Strengthen extension services to provide farmers with technical support and training on soil fertility management.

Soil testing laboratories: Establish soil testing laboratories to provide farmers with access to soil testing services.

Farmer organizations: Support farmer organizations to promote knowledge sharing, innovation, and collective action on soil fertility management.

By Edward Bwengye Kahororo, BA (SWASA) – MUK 1984, MPH – KIT, Amsterdam The Netherlands 1997, MSc WEM – WEDC @ Loughborough University, UK 2007