In the organic production systems that are presently being utilized, tillage can be a significant tool in controlling weeds, preparing seed beds, and incorporating residues. Excessive tillage is a large enemy of soil health. Tillage by itself, can be a beneficial process, if has a productive purpose. A producer once called his process as “surgical tillage”. There was a specific reason for the tillage, performed at a particular time to get a certain goal attained.
Tillage is comparable to a tornado ripping through a trailer park. Home are destroyed and needs to be rebuilt. Same for the microbes in the soil after a tillage pass. The idea with tillage is to incorporate residue into the soil, stimulate weed growth, kill plants, create a seed bed, warm up the soil, or dry out the soil. To minimize the damage of the tillage operation, the tillage should not incorporate the entire A horizon of the soil profile, or the top dark coloured part of the soil. This is where most of the active microbes live, and where a large percentage of the organic matter is contained. Tillage will reduce the organic matter, kill some microbes, and set back mycorrhizal growth. After tillage, the soil must still be covered with the soil armour to protect it from wind and water erosion, and protected the soil from wild temperature fluctuations.
Cover crops will replace many functions of tillage. Cover crop can smother weeds, cycle nutrients, reduce or increase soil cover, help dry out the soil, and warm up the soil all without destroying the microbes habitat. The positive of utilizing cover crops is it will allow the microbial population to grow. Having living roots in the soil will pump more carbon and sugars into the soil, feeding the soil biology.
Utilizing species that are supportive for mycorrhizal growth is critical. Species like Phacelia, clover, and grasses will create strong root systems that will make good homes for microbes. Brassicas in particular will create a lot of sugars in the soil, bumping the bacterial population as the residues rot.
Too many organic producers rely too heavily on tillage as their means of managing their production. It is a quick way to cycle nutrients and control weeds, but it devastates microbial populations, especially the mycorrhizae, and reduces the organic matter in the soil. Reduced organic matter will reduce the microbial population even more long term, and soil fertility. Utilizing green manure plough downs are a step, put more effort is required to help build the soil organic matter.
Nitrogen is one of the most limiting factors in organic rotations. Many utilize legume plough downs, normally sweet or red clover with the hopes of fixing enough nitrogen for the next crop. Including pulse crops in rotation will help fix some nitrogen for the next crop helps extend the rotation. The next step is to include low growing legume crops in the cereal cash crop. Another strategy is utilizing lower nitrogen utilizing crops, or at least crops where having lower protein grain is not a negative marketing factor.
Tuber crops like turnip, radish, and beet will do a good job of recycling phosphate and potassium, assuming those nutrients are deep in the soil profile. They will also scavenge other nutrients like nitrogen and sulphur, as will most other species. Their strength is bringing up phosphate and potassium, breaking up hard pan soils, while increasing humic acid and sugars in the rooting zone.
Weed control under organic systems can be a challenge, particularly perennial weeds. The key is to know the enemy, how it grows, where it’s roots are located, when they germinate, what conditions do they like to grow in, and what do they not like. As an example, Canadian Thistle can be nasty to take out of a field just utilizing cultivation. By including fast growing crops with a deep root system like radish, by mowing the thistles to keep them from getting ahead of the radish, the radish will outcompete the thistles, allowing some cultural control. Quackgrass on the other hand is a tougher pest, but utilizing fall rye has shown to give some control of the quackgrass.
Another option for weed control for organic producers is to grow cover crops and either roll them with a land roller or allow them to frost terminate in the fall. The green material when it rots will give off organic acids. Assuming the ground is covered with the green rotting material, the acid will kill any seedling trying to grow through it. When seeding into this scenario, the openers will move back the rotting residue, allowing what you want to grow come through the furrow opener without any issue. The length of weed control will depend on the amount of green plant material rotting, precipitation, temperature, and microbial populations. If when seeding, too much soil is thrown by the opener, the level of weed control will be reduce.
The take home for organic producers, if tillage is a necessary evil, plan on management practices like cover crops to alleviate the damage. Using cover crops that build organic matter, scavenge free nutrients, build soil structure, and support mycorrhizae is very important to building soil health. Utilizing nitrogen fixing green manure is super but seeding a catch crop so the nutrients are not lost is just as important as fixing the nitrogen.