Green Manure crops and Nematodes.
by Les Boucher
(Sanctuary Point N.S.W. Australia.)
I just thought, that I would add to a subject that Megan touched on in an earlier answer on no dig gardens and that is green manure crops.
I tend to plant both summer and winter green manure crops in gardens that I leave fallow (empty or at rest) every couple of years. It may be one or two beds each time but it helps to add organic matter to the garden bed while encouraging beneficial goodies into the garden.
The benefits to the soil include such things as;
• Increasing organic matter, earthworms and beneficial micro-organisms
• Increasing the soil's available nitrogen and moisture retention
• Stabilising the soil to prevent erosion
• Bringing deep minerals to the surface and breaking up hardpans
• Providing habitat, nectar and pollen for beneficial insects and reducing populations of pests
• Improving water, root and air penetration in the soil
• Smothering weeds
It ensures the biological processes continue to occur by maintaining the microbial activity in the soil. They also protect the habitats of the earthworms and other essential soil invertebrates.
A green manure can have a broader role, often including protecting the soil as a cover crop, but more importantly collecting the nutrients which could be lost by leaching or oxidation and recycling them back to the soil.
The legumes, such as board beans, grey peas, lupins or clovers provide the advantage of little nitrogen factories (rhizobia bacteria nodules) busily manufacturing Nitrogen from the air, along with deep foraging root systems. Cereal grasses such as ryecorn, oats, barley and millet exploit the shallower depths of soil and combine well with a legume.
Rape and mustard are commonly used as green manures, and are known to collect potash. Mustard is also known to rid soils of wireworms. It must also be remembered that rape and mustard are from the brassica family and should never be followed by crops of other brassicas, such as broccoli, cabbage and cauliflower.
Just a quick word on, Root Knot Nematodes. You will notice that I have included the use of rape and mustard seed in this missive. I have deliberately done this as I found that I had Root Knot Nematodes in my garden which I had imported with some (supposedly) organic material from outside of my property.
Root Knot nematodes are a microscopic parasite which is much like a colourless worm and while most Nematodes are harmless, the Root Knot attacks plants of the Solanaceae family.
This includes such things as spuds (potatoes), Tomatoes, Peppers (capsicum), eggplants and chillis.
Normally the first that you notice when you have these little beasties is your vegies starting to wilt or rot and, it won’t be until such time as you pull the plant from the ground, and wash the roots that you will see lumps, or more correctly tumours, formed on the roots. It is here that the mustard comes into its own by helping to control the nematodes.
A word of warning though if you see lumps on the roots of your legume crop ie. Beans, Peas, etc. Don’t worry, as these are just your plants enriching your soil with Nitrogen.
I get my green manure seeds from my local Nursery supply shop and add any legume seed that is left over from two crops ago as it may not be at its peak for planting but, it may just be good enough for a green crop.
Once my Manure crop reaches around knee height (45-50cm /18-19 inches) I chop it back and dig it into the soil where I start planting again within a couple of days.
I hope that this helps others and that they start using these crops to build up the soil in their gardens.