Spread them to a depth of 5–7 cm over the surface and dig them into the topsoil. Animal manure containing a lot of straw may cause a temporary nitrogen deficiency because bacteria decomposing the straw have first call and plants may suffer. So add extra nitrogen or, better still, a complete fertiliser which contains at least 10 per cent nitrogen plus phosphorus and potassium.
Liquid animal manure watered onto leafy vegetables every week or two is an excellent fertiliser. The liquid is made by suspending a permeable bag filled with fresh manure in a large cask or drum of water. After a week the liquid is diluted with water (one part to three parts) for use. There are many convenient, commercially-available, organic-based liquid fertilisers such as fish emulsion and other blends. They combine the advantages of guaranteed nutrient availability with natural components that stimulate soil microbial activity. Seaweed tonics are also included in this group although it’s important to remember that they aren’t fertilisers. Rather, they contain natural hormones that stimulate root growth and build plant defences against stress.
Green manuring is another relatively inexpensive way of adding organic matter to the soil, but the system is usually confined to vegetable gardens when empty beds are lying idle in winter. In our climate, because there are many vegetables which can be grown in winter, there is often little space left over for a green manure crop. However, if you do have an empty bed there are several green manure crops you can use. Seeds of wheat, barley or oats can be broadcast at 30–60 g per square metre in autumn to provide a large bulk of material to dig into the soil in spring. Legume crops which add nitrogen through nodule bacteria in their roots are usually preferred. Suitable crops for autumn planting are field peas and vetches. The recommended seed rate is 15–30 g per square metre. Dig the crops in when they begin to flower in spring. Good summer-growing legume crops for warm northern climates include dolichos (lab lab bean) and cow peas. These are sown in spring and dug in by mid-summer when they flower. A complete fertiliser must be broadcast at one-third of a cup per square metre when sowing all green manure crops.
Water the crops a day or two before digging them in. If the crop is very tall, flatten it and chop up with a sharp spade. After digging, keep the soil damp but not wet, then after three weeks dig the soil over again. It will take another three or four weeks for the organic matter to decompose. If there is any sign of yellowing in the following crop, give side dressings of a nitrogen fertiliser.
Easy-to-handle organic fertilisers are now readily available, with pelleted, slow-release poultry manure being the most popular. Products such as Dynamic Lifter pellets are widely used to fertilise plants in the ground and in containers, both in domestic and commercial situations. Dynamic Lifter variants fortified with extra nutrients are available for lawns and plants with special needs such as roses and fruit trees. Each pellet contains inorganic and organic fertiliser blended together. Organic by-products of animal origin include bone dust, bone meal and blood and bone. Most of these fertilisers contain higher quantities of nitrogen and phosphorus than animal manure, but very little potassium. Nutrients are released slowly. Spread them at 125–250 g per square metre and dig into the topsoil.
This information is from the Yates Garden Guide: fully revised & updated 44th edition, HarperCollins, $39.99. You can have this information and so much more at your fingertips by purchasing the Yates Garden Guide, available at all leading bookstores and Bunnings stores.