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Lime Treatment of Soil

Value Chain
Soils
Climatic Zone
Decision Making
Farming Characteristics
Mechanisation
Labour Intensity
Initial Investment
Maintenance Costs
Access to Finance/Credit
Extension Support Required
Access to Inputs
Access to Markets
Gender/Youth Smart
Description

Soil acidification is a widespread problem across southern Africa, often driven by monocropping with cereals and occurring as a result of erosion, compost decomposition and soil leaching. Applying lime to soil is regarded as a key management practice in agriculture to balance pH, enhancing crop productivity, water penetration and absorption of major nutrients by crops. Most crops grow best in soils with a pH between 6.5 and 6.8. Acidity constrains crop growth below pH levels of 5.5. Agricultural lime is limestone mined as a rock that is crushed into various particle sizes ranging from course to fine particles and can be applied in areas where there is high soil-acidity due to high levels of manganese and iron. Lime texture also determines the speed of absorption in the soil; that is, fine-lime reacts more quickly than more granular lime. However, the use of lime must be managed appropriately to avoid losing other nutrients in the soil. This practice is considered climate smart as it assists with adaptation strategies through improvement of soil fertility, whilst improving productivity at modest application rates, noting that annual application is not recommended.

Technical Application

Before applying lime to increase lower soil pH the following should be considered. Equipment required: soil pH testing kit, protective goggles and mask, agricultural lime, shovels/forks/hoes, and disk harrow, drag harrow or hoe if available.

  • Step 1: Use a pH testing strip to determine soil pH levels, making sure to test surface and sub-surface acidity.
  • Step 2: Measure area of land to be treated in order to determine amount of lime for purchase. Application should be calculated as metric tonne per hectare, depending on soil pH and crop. Lime requirements will differ depending on soil type and level of acidity in the soil. Application volumes can be guided by suppliers.
  • Step 3: Purchase lime according to requirements from agricultural supplier. Savings could be realised if purchasing as a group of farmers.
  • Step 4: Apply lime to the soils at least two months prior to planting directly after harvesting to allow the lime to react with the soil, and positively impact the pH.
  • Step 5: Mix lime and soil well in order to reduce soil acidity. This is normally achieved through disk tilling but can be done manually using a drag harrow or hoe. However, this can be an intensive process.
  • Step 6: Test pH prior to planting to ensure amendments have improved soil pH.
  • Step 7: Plant crops. Monitor crop performance, and harvest results with a view to understanding impact of lime treatment.
  • Step 8: Following harvest, test soil pH again.

Application of lime can be part of an Integrated Soil Fertility Management (ISFM) practices.

While a practical solution, this soil amendment should be informed by research and discussion with extension officers and lime suppliers. On-farm storage and management of lime should be included in this dialogue.

Return on Investment Realisation Period
Crop Production
Fodder Production
Farm Income
Household Workload
Food Security
Soil Quality/Cover
Biological Diversity
Crop/Livestock Water Availability
Wind Protection
Erosion Control
Increase Production
Significant increases in productivity.
Increase Resilience
Sustainable improvements to soil fertility. Application is not required every year.
Additional Information
PDF File
/sites/secondsite/files/tb/CCARDESATechnicalBrief_05_AddingLime_2019-10-17_0.pdf
Benefits and Drawbacks

Benefits

  • Lime treatment can assist farmers to balance pH in acidic soils, optimising water and nutrient use for crop plant growth.
  • A practical and effective way to combat the negative effects of erosion, compost decomposition and leaching on soil.
  • Lime does not need to applied to soil every year.

Drawbacks

  • Adding lime to soils is laborious and should not be considered a short-term solution to balancing soil pH.
  • Over-application or overuse of lime can negatively affect soil quality.

Organic Fertilisers

Value Chain
Soils
Climatic Zone
Decision Making
Farming Characteristics
Mechanisation
Labour Intensity
Initial Investment
Maintenance Costs
Access to Finance/Credit
Extension Support Required
Access to Inputs
Access to Markets
Gender/Youth Smart
Description

Soil fertility is one of the most critical factors needs to be maintained so farmers can continue to grow productive and nutritious crops, especially in southern Africa where soils are often fragile and lacking in plant nutrients. Soils are often quickly depleted if mismanaged, further exacerbated by natural biophysical processes such as rain, wind and/or heat. The use of organic fertiliser can help farmers to improve soil fertility, as they improve absorption of water and add nutrients into the soil, drastically improving crop production. Organic fertilisers are plant (crop residues) or animal-based materials, such as green manure, worm mouldings, compost, animal waste, and sewage residues, many of which may be readily available on the farm, or within a farming community. These products are potential counters to inorganic fertilisers - artificially manufactured chemicals (synthetic) mined from mineral deposits comprising minerals such as nitrogen, phosphorus and magnesium - which are often costly when few farmers can access credit needed to sustainably access such materials. Organic fertilisers are considered climate smart as they utilise (recycle) readily available organic materials to feed soil and crops simultaneously as they add nutrients into the soil and condition it, and thus increase productivity and resilience, while inorganic fertilisers add nutrients to the soil only, and are often expensive.

Technical Application

Organic fertilisers can be produced at the household level or purchased. On-farm production includes stock-piling animal manure, crop residues, and other organic waste, following appropriate guidance for processing and usage.

To apply organic fertilisers the following should be considered:

  • Step 1: Assess field area where fertiliser is to be applied, and fertiliser needs – poor crop performance, low organic matter content, etc.
  • Step 2: Ensure that fertiliser is available in sufficient quantities for application in all target or priority fields.
  • Step 3: Ensure organic fertiliser – especially green manure/crop residues – are broken-down/chopped to aid breakdown/integration with soil.
  • Step 4: Monitor soil nutrient levels and crop performance (in the light of prevailing climatic conditions) to determine success of organic fertilisers.
Return on Investment Realisation Period
Crop Production
Fodder Production
Farm Income
Household Workload
Food Security
Soil Quality/Cover
Biological Diversity
Crop/Livestock Water Availability
Wind Protection
Erosion Control
Increase Production
Improves efficiency and crop yields.
Increase Resilience
Greater production and efficiency results in increased food security and resilience.
Mitigate Greenhouse Gas Emissions
Locks more carbon in the soil and reduces need for inorganic fertilisers.
Additional Information
PDF File
/sites/secondsite/files/tb/CCARDESATechnicalBrief_04_OrganicFertilisers_2019-10-17_0.pdf
Benefits and Drawbacks

Benefits

  • Fertilisers can help restore soil nutrients, improve soil conditions and improve crop production if applied correctly.
  • Organic fertilisers are plant or animal materials that can be produced locally or purchased for application.
  • An appropriate strategy in rural and low-income communities with small holder farmers that can generally not afford synthetic pesticides and inorganic fertilisers.
  • Collective action can minimise the financial cost of implementing organic fertilisers, in terms of shared transportation and storage costs, as well as bulk purchasing power.
  • Use of organic fertilisers can help avoids the leaching of inorganic fertilisers into waterways, which can result in eutrophication.
  • Where farmers do have access to financial resources and/or credit, organic fertilisers should be used in combinate with inorganic application.

Drawbacks

  • Manure and other types of organic fertilisers require management, and relevant storage mechanisms. If not stored correctly, investment can be lost as nutrients can be lost due to exposure to the elements.
  • It can be costly to transport if sourcing from off-farm
  • Weed seeds can be present in manure, increasing labour requirements for weeding.
  • If not produced on-farm, organic fertilisers, while beneficial can require access to sustainable financial resources or credit to implement correctly.
  • Requires extension support to ensure that fertiliser requirements are being met.

Biochar

Value Chain
Annual Average Rainfall
Climatic Zone
Water Source
Decision Making
Farming Characteristics
Mechanisation
Labour Intensity
Initial Investment
Maintenance Costs
Access to Finance/Credit
Extension Support Required
Access to Inputs
Access to Markets
Gender/Youth Smart
Description

Biochar refers to a fine-grained charcoal, rich in organic carbon compounds, used to improve soil quality through enhanced nutrient and water holding capacity of soil, reducing total fertiliser needs. Biochar is a stable solid produced from the controlled burning of plant and waste feedstock, including wood chips and pellets, tree bark, crop residues (straw, maize stovers, nut shells and rice hulls), grain, sugarcane bagasse, chicken litter, diary manure, sewage and paper sludge. Biochar is used as a soil conditioner as part of soil amendment strategies, improving the workability of soil, particularly those with heavy clay components.. The application of biochar to soil is a strategy to minimise the climate and environmental impact of cropland systems, such as the application of synthetic fertilisers, and improve soil quality through enhancing its physical-chemical characteristics. This agricultural practice improves soil structure, nutrient cycling and water retention, and the high stability of biochar carbon compounds contributes to the reduction of green-house gas emissions by increasing carbon sequestering in soils. Biochar is shown to be effective in improving soil conditions in acidic, sandy and clay-rich soils, improving the physical characteristics, and is classified by the FAO classifies as an adaptation strategy and contributes to mitigation of climate change as the processes captures and stores carbon in soils create other secondary socio-economic benefits, through additional fuel sources, and economic opportunities for production. Biochar can either be purchased or produced on-farm on a small or large scale. Collective action may benefit communities, so discussion with neighbours and community leadership may be necessary, especially if a biochar.

Technical Application

To effectively implement biochar the following should be carried out. Tools required – shovel and a metal sieve.

  • Step 1: Acquire charcoal from local vendor, and sieve or grate the charcoal into fine material in a pile. Biochar should not be applied to soil directly after production. It should be allowed to ‘rest’ for one to two months.
  • Step 2: Rotate the pile every 2-days for a period of up to 10-days (total).
  • Step 3: Prior to application, aim to wet (but not waterlog) biochar stock with water or preferably urine. If done when still warm, it will fracture the charcoal, increasing surface area for absorption.
  • Step 4: Spread the biochar evenly across soil prior to planting and let it settle or mix with the top layer of soil. One to three kg/m2 is recommended, depending on the degree of soil required.
  • Step 5: Regularly monitor soil pH, water retention and soil texture, keeping records if relevant to ensure that improvements are realised, and negative impacts do not arise.

Biochar can be produced on-farm, but will require collection of plant and waste feedstock (see above). Biochar can be produced on-farm using a trench. A biochar trench is a dug recess where crop residues are burned to create charcoal. Tools required are a shovel and one or more roofing sheets (one-metre long).

  • Step 1: Dig trench 50 to 70 cm deep, and one to two metres long, ensuring that roofing sheets fully cover the trench void.
  • Step 2: Start a fire in one end of the trench, throwing in loose crop residue or other organic waste, keeping the fire under control (not creating large flames and smoke).
  • Step 3: Keep fire burning until trench is full of char.
  • Step 4: When the trench is full, and flames have burned-out, cover the trench with the roofing sheet, sealing edges with loose soil, trampling it down to ensure closure.
  • Step 5: Leave the covered trench for five to six hours to extinguish.
Return on Investment Realisation Period
Crop Production
Fodder Production
Farm Income
Household Workload
Food Security
Soil Quality/Cover
Biological Diversity
Flooding
Crop/Livestock Water Availability
Wind Protection
Erosion Control
Increase Production
Makes nutrients more available to plants and increases water retention. Can increase pH.
Increase Resilience
Improves water retention. Remains in the soil for a long time.
Mitigate Greenhouse Gas Emissions
Capturing carbon in soils thereby reducing emissions.
Additional Information
PDF File
/sites/secondsite/files/tb/CCARDESATechnicalBrief_03_Biochar_2019-10-17_0.pdf
Benefits and Drawbacks

Benefits

  • The production and application of biochar reduces GHG emissions of cropland systems due to the properties of the biochar itself, and reduction in the application of synthetic fertiliser.
  • Can improve physical and chemical composition of soil, especially in acidic, sandy and clay-rich soils; soil nutrient cycling and water retention.
  • Can reduce fertiliser and irrigation requirements.
  • Potential socio-economic opportunities for biochar producers, if not produced on-farm.
  • Improved food security from production of secondary fuel source.
  • Provides an appropriate and sustainable mechanism for dealing with crop residues and biomass.
  • Can be mixed with compost during application to increase performance of soil amendments.

Drawbacks

  • Requires sustainable non-wood supply of organic matter for production so as not to increase deforestation.
  • Long-term impacts not fully understood.

Green Manure

Value Chain
Climatic Zone
Water Source
Decision Making
Farming Characteristics
Mechanisation
Labour Intensity
Initial Investment
Maintenance Costs
Access to Finance/Credit
Extension Support Required
Access to Inputs
Access to Markets
Gender/Youth Smart
Description

Green manure (otherwise known as cover crops), is a climate smart fertiliser process that involves growing plants (mainly legumes) and distributing uprooted or sown crop-parts to wither and cover soil. It provides soil coverage to enhance biological, physical and chemical properties of soil while mitigating soil erosion, supressing weed growth, adding biomass to soils, improving soil structures, promoting biological soil preparation, and reducing pests, diseases and weed growth. These functions can increase economic return, reduce the need for herbicides and pesticides, while increasing productivity and potentially the quality of crops. It can also increase soil nitrogen, improve soil fertility, conserve soil humidity and reduce fertiliser costs. Green manure also has low management costs, presents good conservation characteristics, and improves biodiversity. Green manure is a feasible and sustainable option for farmers to improve soil quality and productivity, depending on local context and availability of different leguminous plants that best fit for farmers’ cropping systems. Examples of leguminous plants that can be used in southern Africa include: Mucuna (Mucuna pruriens); Sunhemp (Crotalaria juncea), Lab-lab (Lablab purpureus); Pigeon pea (Cajanus cajan); Cowpea (Vigna unguiculata) and Butterfly pea (Clitoria ternatea). Green manure has climate smart benefits as contributes to sustainable maintenance of agricultural production without the use of chemical fertilisers and depending upon the cover crop can contribute to adaptation of agricultural practices to climate change. Furthermore, coverage of soil with additional plant material can assist with carbon sequestration in soil. Not only does growing a secondary green manure crop provide a soil amendment benefit, but the crop can also be used as fodder for livestock. As the most common green manure plants are legumes, the pods and seeds can be fed to livestock while leaving the crop residue to perform the cover crop function in in the fields.

Technical Application

To effectively apply a green manure approach, the following should be considered:

  • Step 1: Select legumes that grow well under local conditions and in local soils. Green manure crops should be resilient and require few crop management practices. A thorough investigation should be made to ensure that green manure crops are appropriate for the local conditions in terms of rainfall, climate, soil pH and texture, and salt tolerance.
  • Step 2: Identify the appropriate time for planting the green manure crop to ensure growth, but not impacting the primary crop. Especially if the secondary crop is a climber/creeper. Main crop may need to be mature before planting the manure crop, as if a creeper, it may outcompete or constraint growth of maize or sorghum plants.
  • Step 3: If seeking to enrich soil properties, the farmer must allow crop residue to remain in the soil longer. This is particularly relevant with multiple uses – e.g. soil amendments and livestock fodder. In these cases, pods can be harvested for fodder, and the remaining plant residue left in the field to cover the soil.
  • Step 4: Crop planting should be alley cropped between the primary crop rows, allowing management of the primary and secondary crops, also reducing the competition between the primary and the secondary crop. If the secondary crop also has pest management properties, it may be beneficial to consider boundary planting.
  • Step 5: When harvesting the secondary crop, the farmer should consider leaving the residue in the ground. If it is uprooted, it should left on the soil surface. A common mistake is to remove it from the field and accumulate it in one location, missing the benefits of cover-crops, and exposing the residue to decay.

Unless local examples are available, small test plots should be used to test different cover crops to determine which is the most appropriate, and if necessary, demonstrate value to farmers and communities. As the secondary (green manure) crop is not a direct cash-crop, you may need to ensure expectations are measured. It may take several years to develop enough green manure crop to contribute to crop production; hence, crop production has to fit around existing cash/subsistence crops. Furthermore, benefits may not be realised within a single planting season., e.g. Nitrogen may only be available in the soil in the subsequent season.

Return on Investment Realisation Period
Crop Production
Fodder Production
Farm Income
Household Workload
Food Security
Soil Quality/Cover
Biological Diversity
Flooding
Crop/Livestock Water Availability
Wind Protection
Erosion Control
Increase Production
Green manure can maintain or increase agricultural productivity through improved soils.
Increase Resilience
Adjustment of practices to include cover crops allows farmers to diversify crop types, and produce their own fertilisers.
Mitigate Greenhouse Gas Emissions
Reduction in carbon released from soil.
Additional Information
PDF File
/sites/secondsite/files/tb/CCARDESATechnicalBrief_02_GreenManure_2019-10-17_0.pdf
Benefits and Drawbacks

Benefits

  • Green Manure is a non-tillage method that promotes soil fertility through enhancement of soil organic content. In doing so, it mitigates erosion, maintains soil humidity, and promotes biological activity.
  • Many green manure plants can be used to feed livestock if there is an excess
  • Green manure cover crops also make organic matter to apply – compost requires work and time to develop, whereas this approach sees it added immediately.
  • Cover crops can reduce weed competition by shading soil.
  • If using legumes, they can thrive in poor quality soils.
  • Cover crops such as Cow pea can also be used for animal and human consumption.

Drawbacks

  • Require access to seedbanks for legumes and other viable cover crops.
  • May require the testing of crops in test plots prior to implementation.
  • If so, community action may be required to test varieties and make decisions.
  • Farmers may require more land to plant the same amount of the main crop, as they need to be intercropped with the cover crop. This can be unattractive to some farmers.

Compost

Value Chain
Climatic Zone
Water Source
Decision Making
Farming Characteristics
Mechanisation
Labour Intensity
Initial Investment
Maintenance Costs
Access to Finance/Credit
Extension Support Required
Access to Inputs
Access to Markets
Gender/Youth Smart
Description

Compost is a biological process where micro-organisms recycle decaying or decomposing organic matter to produce a soil conditioner that can be applied as an additive to improve soil conditions. Composting takes place in the presence of oxygen (aerobic conditions), and with adequate temperature and moisture, transforming organic matter into plant-available nutrients. Compost can comprise organic plant and/or animal matter, and/or residues including leaves, dead roots, manure, urine, bones, and nematodes, amongst other organic materials. As it is generally rich in nutrients, the application of compost can naturally fortify soils, acting as a fertiliser, with soil humus or natural pesticide increasing the resistance of plants to diseases, foreign species and insects. The amount of organic matter in different soils depends on the soil type, vegetation species, and other environmental conditions, such as moisture and temperature. Thus, the application of compost may add important nutrients to soils that can benefit vegetation growth. Rainfall, temperature changes and other biophysical factors may result in a diminishing return of compost benefits to soil health. Therefore, the application of compost to soils should be a continuous practice, in order to increase physical, chemical and biological benefits. There are two main composting systems: Open Systems (compost piles or pits) or Contained Composting – see technical application below. This is a climate smart approach as it recycles readily available organic materials from a farm for use within the farming system, plus it avoids the use of chemical fertilisers. Composting is a climate smart approach as it reduces the need for chemical fertilisers, contributes to soil amendments that support adaptation to climate change, and helps retain soil fertility, which in turn aids agricultural productivity.

Technical Application

To effectively undertake composting:

  • Step 1: gather compostable materials - rests of harvests, animal manure and dung, organic kitchen waste (fruit and vegetable waste), other food waste, edible oils and fats, wood shavings, paper products (not printed), hair cut waste. Avoid non-compostable materials such as chemical residues, glass, metals, plastics, carcasses, cooked leftovers or meat.
  • Step 2: Chop/cut materials to achieve optimum particle size is between 5 – 20 cm – this will assist decomposition. Wire mesh can be used to sift smaller non-organic particles.
  • Step 3: Add water regularly using a watering-can to assist decomposition, ensuring that the materials do not become water logged.
  • Step 4: Using a pitchfork or shovel, turn-over or rotate compost materials regularly as oxygen is a key component to the decomposition process.
  • Step 5: If available, add earthworms (known as vermiculture) to compostable material, which enriches soil, enhances plant growth (hence yields) and suppresses disease.
  • Step 6: Once compost material has been decomposed (three months to two years, depending on climate and composting material) it will be a fine, dark material. Screen the material to remove large particles and mix with soils in gardens or fields prior planting and around plants throughout growing period.
  • Step 7: If compost does not include animal manure/waste it can be applied to crops as an organic fertiliser at any point up to harvest. If it does include animal waste, it can be incorporated into soil not less than 120 days prior to harvest, especially where edible portion of crops has been in contact with the soil surface.

Additional notes:

  • For Open Composting System (Piles): select a level area or dig a pit with a level bottom away from developed areas, chop collected materials into piles, turn over or rotate and add water to material regularly (weekly or bi-monthly). Cover pile if there is heavy rain to prevent materials from washing away and becoming water-logged.
  • For Contained Composting Systems: construct a container unit from mesh, wooden panels, bricks and other suitable building materials, fill the container with chopped material, turn over or rotate, and add water to material regularly (weekly or bi-monthly). Keep compostable material covered.
Return on Investment Realisation Period
Crop Production
Fodder Production
Farm Income
Household Workload
Food Security
Soil Quality/Cover
Biological Diversity
Flooding
Crop/Livestock Water Availability
Wind Protection
Erosion Control
Increase Production
Retaining or improving soil fertility to ensure increased or sustained agricultural productivity.
Increase Resilience
As climate change places increased pressure on land management, compost can contribute to soil amendments to aid adaptation.
Mitigate Greenhouse Gas Emissions
Use of compost to amend soil avoids the use of chemical fertilisers and reduces greenhouse gas emissions.
Additional Information
PDF File
/sites/secondsite/files/tb/CCARDESATechnicalBrief_01_Compost_2019-10-17_0.pdf
Benefits and Drawbacks

Benefits

  • Composting is an effective and low-cost option to recycle organic matter that can improve soil nutrient health.
  • Composting in scalable, based on need and available organic materials.
  • Moisture and oxygen are very important. Ensure that compost materials are moist and regularly rotated to optimise decomposition conditions.
  • Cover during extreme weather events (heavy rain, extreme heat, high wind etc.).
  • Add earthworms to the material to increase decomposition and speed up process.
  • Compost should be regularly added to soils to increase soil organic nutrients.

Drawbacks

  • Developing productive compost material, with beneficial nutrient is not a quick process, and can take up to two years for productivity to reach optimal outputs.
  • Faster methods require more energy and inputs as significant amounts of organic material is needed, material must be shredded/chipped, and compost piles need to be turned every three days.
  • While composting is scalable, the amount of available organic material may be a limiting factor.
  • Composting plant material must include removal of any diseased plant material and weed seeds should be avoided.
  • Earthworms will need to be sourced to improve the productivity of composting operations.

Earthworms can be sourced from a worm farm – if worm farms are not available, you can create your own by purchasing worms from an agricultural supplier. Worm farms can also be purchased as kits.

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