Subsurface fertilisation is the agricultural practice of placing compressed balls of fertiliser, known as briquettes, deep in the soil. The balls of fertiliser are known to gradually release nitrogen, feeding the crops with the desired nutrients. This practice is usually carried out in flooded fields and although originally used for urea application in irrigated rice, it can be used with other fertilisers and crop types. Sub-surface fertilisation prevents the loss of nitrogen during floods as the application is placed 7-10 cm deep in the soil, converted to ammonium, which is much less mobile than nitrates. Only about 4% of nitrogen is lost to the environment when applying in the sub-surface, as compared to 35% when nitrogen is applied using the broadcasting application practice. Urea briquettes are small (~2 cm diameter), and home-made manure briquettes – more practical and applicable for crops other than rice – are larger – up to 10 cm in diameter.
This fertiliser application technique is considered climate smart as it maximises fertiliser inputs, increasing productivity and providing a mechanism for adapting to climate change by amending soil properties to remain productive.
To effectively implement subsurface fertilisation, the following should be carried out. Use of briquette machines to produce 1 to 3 grams of briquettes that are larger than conventional fertiliser granules is recommended:
- Step 1: Prior to application, dig small holes 7 to 10 centimetres deep along planting rows in drained rice paddy or regular field, ideally located in the centre between a location where four plants will be planted.
- Step 2: Place the briquettes in the whole, below the soil surface, and cover with dug soil.
- Step 3: Crops should be planted within seven days of fertiliser application.
Following are the main steps for making your own briquettes. Making briquettes leading up to planting is more effective, as they are not stored for too long. A standard briquette machine can be purchased for between USD 3,000 and USD 6,000.
- Step 1: Collect manure from cow and/or horse waste.
- Step 2: Allow the manure to moderately dry (so it is possible to handle), but not for extensive periods, otherwise it will degrade. Keep manure out of direct sunlight, or when processing, remove the outer layer before manufacturing briquettes, and do not leave exposed, especially during rainy periods.
- Step 3: Press manure into briquettes using briquette press machine – see directions below to make your own home-press.
- Step 4: Allow the briquettes to dry in a cool, dry location, and store for later use.
To make your own large manure briquette press using household items, follow the instructions below:
- Step 1: Cut the top off a straight-sided 2-litre plastic soft drink bottle at the top of straight side.
- Step 2: Obtain a tinned food can that is just smaller than the diameter of the bottle. Preferably leave tin un-opened.
- Step 3: Line the bottle with a plastic bag.
- Step 4: Place slightly damp manure (cow, horse or both) inside the bag, inside the bottle, filling the space.
- Step 5: Place tin on top of manure.
- Step 6: Place small plank of wood on top of the tin.
- Step 7: Place your foot on top of the piece of wood, and slowly apply pressure to the tin, pressing the manure down, adding more manure if it compresses further than the depth of the tin.
- Step 8: When the manure will compress no more, remove plank and tin, and draw the compressed manure from the bottle, removing the plastic bag to reveal a cylinder of compressed manure.
- Step 9: Slice with a sharp knife to discs 2 to 3 cm thick, and use a piece of 2 cm diameter metal or plastic pipe to punch a hole through each disc. Reuse the
- Step 10: Allow to air dry as individual rings in a cool dry place. As soon as they are strong enough, you can hang the rings on wire to continue to dry. Use in fields within a month of manufacture. The ring increases surface area, and speeds-up the drying process.
- Briquette Machine 2019. Horse manure briquette machine specifications. Briquette Machine website.
- FAO 2002– On Farm Composting Methods; Land Water Discussion Paper 2. FAO, Rome, Italy.
- International Fertiliser Development Centre, Fertiliser Deep Placement. IFDC Website.
Benefits
- This application preserves the nutrients deep in the soil and nourishes the soil making nitrogen available to the crops throughout their growth cycle.
- Maximises fertiliser application, as little is lost to the atmosphere.
- Farm waste such as manure can be repurposed into briquettes for subsurface fertiliser application.
- Can provide a revenue generation opportunity for enterprising community members.
Drawbacks
- Requires additional labour to gather material, and to make briquettes.
- There is a financial commitment for purchasing briquette-making equipment.
- Briquettes can be made by hand, but it requires additional labour and time.
