Green manure crops

Article shared with permission from Rob Stokes of ROC Systems.

Green manure crops are similar to cover crops except they are incorporated into the soil. They are hugely beneficial to your soil, however, the ploughing process causes losses of soil carbon and organic matter.

One incredible fact to note is that if you plant multi-species, you can achieve 50 per cent more organic matter, higher water holding capacity, deeper topsoil and more organic matter to feed your microbes as compared to the traditional mono-cropping, usually Katambora Rhodes grass.

There are two schools of thought when it comes to choosing which cover crop to plant. You can go the scientific route and buy, usually imported seed, to accurately target your problem areas in the soil. Or you can just go for maximum bulk which may not hit the target as accurately. However, I believe that getting locally sourced seeds like sunflower, sun hemp and sorghum which are cheap, available, and easy to germinate will give you the bulk of organic matter. This also means that you don’t have to buy certified seed but simple grain as you are not looking for maximum yield, just maximum bulk. Quantity trumps quality and don’t forget that all the weeds that come up with your green manure crop will give you almost countless diversity for free. (Weeds now become your friend.)

The basis for maximising your commercial crop is healthy soil. This is best achieved with maximum bulk of organic matter, and you can inoculate your soil with added bacteria and fungi which can simply be seed-treated before sowing. This could include kelp extracts, Trichoderma, mycorrhizae fungi and biological nematicides.

If you can grow this cover crop for three months, and plough it in, you can also add effective micro-organisms (EM) which will greatly speed up the decomposition and allow you to take soil samples (including nematodes) which will help you formulate the correct fertiliser (nutrition) and the correct nematicide if necessary. Generally, increasing your organic matter will increase your free-living nematodes which will naturally help to control your root-knot nematodes.

It is important not to try and go from zero to hero and taking regular soil samples will show you what inputs you can start cutting back on. A healthy plant generally is far more resilient against pests and diseases, including nematodes, and we can therefore go to a more corrective approach on chemicals and fertilisers as opposed to routine applications which will save on money, time and effort without risking any yield loss and help achieve better quality.

Continuous tobacco has never been recommended. However, ploughing in a thick, dense and tall cover crop will greatly improve your soil health to the point where continuous tobacco is now a safe, reliable, healthy and viable option.