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Lesson 12 – Part A: WHAT IS A GREEN MANURE?
Lesson 12 – Part B: PREPARING SEEDS AND BED
Lesson 12 – Part C: GROWING A GREEN MANURE
Lesson 12 – Part E: GRADUATION (optional)
Preparation for Lesson 12:
Please read through Lesson 12 text for students, and please note that Part D nitrogen fixation text is for senior students only.
You will need to order some suitable bulk seed for this lesson. The smaller the seed, the larger the area it will cover by weight. If you want a green manure legume to fix nitrogen, remember to order the inoculant with the seed. For a list of suitable seed suppliers for each state, click on the Open pollinated Seed Suppliers link on the left side of this web page.
The list of seed suppliers includes those who offer green manure seed mixes of grains with suitable legumes, as not all legumes compete well in mixed plantings. You can sow these mixtures of seed if you prefer but, remember that in doing so, you will be using two crop rotation groups (green and dark grey) at once, and you will have to adjust your crop rotation accordingly.
Seed suppliers will be able to advise the quantity of seed you will need if you provide them with the overall size of the bed area. Further information on green manure and cover crops, plus a table of individual green manure grains and legumes that includes suitable inoculants for nitrogen fixation, sowing times in different climates, and uses of each variety, can be found in Easy Organic Gardening and Moon Planting pp 11-18.
To divide the seed for even broadcasting, you will need a set of kitchen scales and a collection of small containers to hold portions of seed.
For preparing the bed, you will need some organic-allowed, poultry-based fertiliser and seaweed extract, some short sticks, and some knitting yarn or string.
This lesson can be given at any time you wish to grow a green manure crop. However, we do recommend that a green manure crop be sown wherever possible towards the end of the school year to re-vitalise the soil for the coming year. The crop will protect garden soil over the long holiday period and, if it dies off during the break, the roots alone will add considerable organic matter to the soil.
Green manures are not only useful in new beds, they can be used to add organic matter to soil or provide mulch whenever you have a garden bed that is not being used (lying fallow). In areas where heavy rain can wash nutrients from soil, green manure crops are better at holding nutrients in upper layers than just allowing beds to lie fallow. Organic matter needs to be replaced regularly in soil to keep it healthy. If you include green manures in your program, you will soon be pleased to see the improvement in your plants and soil. Don't forget to practice crop rotation with green manures, too. Don't always sow the same grain or legume or you can end up with some diseases through not breaking the pathogen's reproductive cycle.
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Preparing the seeds
It will probably be easier if the weighing and dividing of the seed is done before students start working in the garden. If you measure the length of the proposed green manure area before the lesson, you can calculate roughly how many equal sections of between 75 cm and 1 metre that you can divide the length into. Double this amount to find the number of small containers you will need to hold the batches of seed. Any clean yoghurt or fast food containers are suitable for this purpose.
If your kitchen scales don't have a button that allows you to reset to zero after the empty container has been placed on the scales, show students how to subtract the weight of the container from the final weight to find the actual weight of the seeds.
Preparing the bed
When sowing uninoculated legume seed, you will have to include enough nitrogen in the fertiliser for good growth, and avoid lower leaves of legumes becoming yellow. This occurs when the plant contains insufficient nitrogen or magnesium and the plant draws these elements from the lower leaves to the young tips in an effort to keep growing.
If sowing an inoculated legume, add seaweed extract tea to the bed but only add a small quantity of fertiliser because nitrogen fixation will not occur in legumes if soil contains excess soluble nitrogen.
A suitable soil pH (6.25-7.5) will give the best results when growing green manure legumes, as they do not do well in acidic soil. If the bed is very acidic and contains little organic matter, grow a green manure grain as this will help improve both the soil structure and the soil organic matter content, which will make it easier for you to improve the pH for growing food crops.
When applying lime, thoroughly mix an adult handful into a full watering can and apply this amount per square metre. Use dolomite for preference to maintain the correct calcium:magnesium balance in soil, except in parts of south-east Queensland where soils can be high in magnesium, where you should use agricultural lime.
If soil pH is above 7.5, the pH can be reduced by adding elemental sulphur (flowers of sulphur). Alternatively, an adult can dig in some well-rotted cow manure, if the manure has not come from an area where herbicides have been used. The green manure roots and the breakdown of organic matter will release hydrogen ions into the topsoil, replacing calcium ions and helping you to bring the soil pH to a more suitable range.
However, due to health and safety concerns, we do not recommend allowing children to work with uncomposted manures, or using any uncomposted manures except before growing green manure crops.
Raking furrows across the bed will avoid students having to walk on the bed while raking.
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A brushcutter or whipper-snipper is perfect for the task of cutting down green manures, and plants can be chopped by removing about 10 cm of growth with each pass of the brushcutter, if you want to dig the plants into the topsoil. Roots of perennials, such as alfalfa or pigeon pea, will have to be dug up, or they will keep growing. Otherwise, the crop can be slashed close to ground level and the foliage left on the surface as mulch while the roots break down to provide a mass of humus in the soil.
Inoculated legumes have their highest nitrogen content just as they start flowering, and they should be cut down at this time, before a lot of nitrogen goes into pod production. Legumes that are cut down after they have produced pods are used as ‘pea straw’ for mulching.
When the slashed green manure foliage has browned off, you can plant seedlings through the mulch, or make drills through the mulch to sow seed. Farmers call this 'stubble planting' or 'no-till sowing'.
The bacteria that break down the organic matter will require some nitrogen as they work, but when the bacteria die off the nitrogen will be returned to the humus and is available for your vegetables to use. If you have to plant or sow before the break down of the green manure is well under way, put some compost in each planting hole and add some liquid fertiliser to the bed so that seedlings won't be temporarily short of nitrogen.
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Preparation for Graduation:
Schools that registered on the 'Home Page' of this program as participants in the BFA Organic School Gardens program can receive a PDF template for an 'Organic Gardener' certificate that can be filled in and presented to students who have completed the program.
• To order your template, email: education@bfa.com.au
A graduation class is optional. You may wish to present a class where students write about, or informally discuss, what they enjoyed most about the program, and present certificates to students at that time.
Or, you may prefer to present certificates to students after completing Lesson 12, or your school may prefer to present the certificates with other school awards at the end of the year.
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