Organic Farming Notes
Kenrick Riley grows organic herbs and vegetables at Georgica in the NSW Northern Rivers. He is attempting to breed a variety of hemp as a summer grain crop for the sub-tropics.
These notes are especially targeted to new farmers who may be converting pasture to small or medium scale hemp growing and would like to grow hemp sustainably.
If the soil was compacted by livestock for any length of time, then deep ripping is recommended. This will aerate the soil and activate good bacteria and fungi, which cannot thrive in compacted soil. It will also make phosphorus, potassium and other minerals more available to the crop.
Hemp is very sensitive to soil compaction. Although it can be grown on a variety of soil types, it needs a loose seed-bed to develop a tap root. Unlike most plants, hemp seed has to push its large seed capsule up through the soil ahead of the seedling. Hence, shallow planting and loose soil are essential.
After deep ripping, check the pH of the soil.
Compacted soils are often acidic. Hemp prefers a neutral to slightly alkaline soil (pH 6 – 7). If the soil is acidic, apply agricultural lime at the recommended rate to adjust this. An addition of gypsum will help soil if it is cloddy or high in clay. This can be dug in at a rate of a couple of handfuls per square metre on small beds – or follow the recommendations for broad-acre application.
Raised beds are an advantage in heavy soils or where there is danger of waterlogging. Hemp is generally planted in raised beds for seed production – or where smaller areas are cultivated. However, for fibre or bulk seed production, the crop is usually grown in broadacre blocks to limit “edge effect” or branching.
The benefits of a green manure crop …
After initially working the soil, an ideal preparation for hemp is to first plant a green manure crop that can be slashed and ploughed back in 3-4 weeks before sowing hemp seed. Depending on the green manure crop, it will add a mix of organic matter and nitrogen to the soil.
If possible, select a variety of green manure seeds (according to season and climate) and sow them as a mix. A selection could include any legumes (clover, cow pea, lab lab, chick peas, vetch etc), mustards (other brassicas), rye grass, millet etc. Green manure cropping is a relatively inexpensive exercise and seed merchants stock a variety of types suited to local climates.
Most Australian organic certifying bodies will consider a dispensation to use non-organic green manure seed – because the crop is not grown for human consumption, and bulk organic green manure seed is still largely unavailable. However, ask the merchant to verify the seed was not genetically modified nor was coated with pre-emergent pesticides.
A rule of thumb is to let the green manure crop grow till early flowering stage before slashing and ploughing in. However, timing will also be governed by when the hemp crop needs to be planted.
Once the green manure has rotted in the soil – and prior to sowing hemp – add any composts, fertilisers or other minerals to the soil and lightly till them in. This final tillage can also be used to form-up beds or remove any weed regrowth after the green manure ploughing.
Bulk organic compost is becoming increasingly available by the delivered truckload in many major towns – often created out of recycled garden prunings from the local municipality. There are also a number of composted chicken fertilisers available, which are a source of additional nitrogen.
If the soil is particularly low in phosphorous, a rock-phosphate powder can be included with the compost/fertiliser application and all tilled in together.
Where possible, rotate hemp with other cash crops, green manures or livestock – so hemp is always sown in a fresh paddock.