Soil Blocks - Japan - ARI
by the Asian Rural Institute
page developed by Rina Tanaka, ARI Volunteer
submitted October 2020
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Lettuce seedlings grown in soil blocks; before the blocks are separated (left), an individual block (right)
Soil Blocks
What are soil blocks and why do we use them?
At ARI, we sometimes use plastic pots to grow seedlings before they are transplanted in the fields.
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A black plastic pot (left), a basil seedling grown in a plastic pot (right)
Although these pots are convenient, plastic might not be readily available depending on where you live. Soil blocks are environmentally friendly alternatives to these plastic pots for growing seedlings.
Soil blocks, as the name suggests, are cubes of soil that we can sow seeds and grow seedlings in. Not only can we make them out of ordinary materials, it has one significant advantage over plastic pots. When we remove a seedling from a plastic pot to transplant it, we end up disturbing the roots of the seedling. Disturbing plant roots stresses the plant and might slow down their growth. However, with soil blocks, we can directly insert a soil block containing a seedling into the soil when transplanting, which does not disturb the roots as much.
How do we make soil blocks?
One batch of soil blocks is a 70cm × 70cm square, 7cm in height. From this one batch, we can make 64 (8×8) soil blocks.
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One batch of soil blocks can produce 64 soil blocks
1. Preparing a soil mixture for soil blocks
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A mixture of leaf compost and subsoil
Mix equal amounts of leaf compost and subsoil (at a 1:1 ratio). Leaf compost can be substituted with other types of compost. However, when using composted manure from other farms, you should check if the animals there are treated with antibiotics or chemicals. Subsoil is just a layer of soil under the topsoil. (At ARI, our subsoil is red!) Since it exists deep under the surface, it is less likely to contain diseases and weed seeds. The purpose of mixing subsoil into the leaf compost is to make it sticky – without any soil, leaf compost will not stick to each other and will not stay in a cube form.
2. Making a frame for soil blocks
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Use wooden boards to make a frame for the soil blocks. The boards we use are 70cm in length and 10cm in height, with a line marking the 7cm height point. To make one batch of soil blocks, we use four wooden boards, each forming one side of a square.
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A frame constructed with the boards
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To prevent the frame from moving, we can put stakes around the boards.
3. Adding water and kneading the soil mixture
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Put some soil mixture (mixed leaf compost and subsoil) inside the frame and pour in some water.
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Kneed the soil mixture thoroughly, adding more soil mixture and water until we fill up the inside of the frame with wet soil.
Determining how much water to put in can be difficult. If there is not enough water, the soil blocks will fall apart when you cut them up later. One way to tell is when you insert a knife through the batch of soil mixture, you should be able to cut through it without much soil sticking to the blade. You will get the hang of it after making soil blocks multiple times!
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Soil mixture (after it is mixed with water and kneaded) filling up the inside of a frame
4. Cutting the wet soil mixture into blocks
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Once the inside of the wooden frame is filled with kneaded soil, cut it into 64 pieces with a knife. Make sure the blade reaches the bottom, especially around the edges!
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One batch cut into 64 cubes
After we remove the wooden boards, sow a seed in each soil block and wait for the seedlings to grow!
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Sowing seeds in the soil blocks: make a hole with your finger (left), sow seeds and covering the seeds with leaf compost (right)
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Waiting for the seeds to germinate
How do we transplant soil blocks?
It is very easy! Once the seedlings in the soil blocks are ready to be transplanted, we can detach the soil blocks from each other (a knife might be helpful for this). Then, we dig a hole in the soil bed and bury the soil block containing the seedling.
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