A system much used in Biodynamic growing but not widely used even with organic growers but getting better known and practiced.
The value is significant. The microbes which are vital for the plant's health need to be kept alive and thriving even though there isn't a crop in just now. My observation is that with mulch over fallow, the ground dries out with a conventional in-ground garden. With a cover crop, the soil can remain moist if the crop is watered as needed. This way the soil and its invisible inhabitants are kept in good spirits until the next food crop is planted. And with little effort, the organic matter content of the garden is increased. Leave the roots in and chop down the top, dig in if you wish or just chop and drop.
The varieties of plants used for cover crops are endless. Ranging from whatever you have to spare, to bird-seed to specialised seasonal crops usually high in legumes.
I've used the 'what I've got to spare' system and the 'bird-seed' system. Something growing is better than nothing. But ... I've found the bird-seed to be heavy in grasses - millet and corn especially. Grasses are fine, have excellent fibrous roots. But their growing-points are well down near the roots (that's why you can mow grass and rarely kill it). That's a two-edged sword ... The grasses cut down and drop just fine but they grow back up again! So you're revisiting the chop and drop several times before the plants run out of energy. By this time I've run out of energy too.
Vary the plants used to get a spread of nutrients and select plants which will die once cut down. These include Sunflowers, Buckwheat, Lucerne (Alfalfa) various Peas and Beans and the very available Mung Beans. The Peas will often shoot again but a couple of cuts and they die out. Now, I read about legumes increasing the nitrogen content in the soil. Yes, they do but they need specific bacteria to make that happen. There are inoculants available and they have to be obtained from specialist suppliers, sometimes this is not very feasible. I do use legumes but don't inoculate. My Lucerne which is 'Alfalfa' escaped from a tray of spent sprouts, does not have nodules on the roots. But it does grow very well, has big enthusiastic roots and flowers and re-seeds happily. I chop it down regularly for mulch. My el cheepo version of Lucerne Hay.
So I've found that if I use seed mixes containing grasses, I need to uproot the whole lot and lay it down roots and all on top of the soil. This is not the most satisfactory way of doing things, the microbes in those roots will probably die when exposed to air and sun. Not quite what I had in mind!
In the photos you'll see that mostly the cover crop is quite dense. If using large seeds like Sunflower and Buckwheat, around .5kg per 1 square metre at a rough guess would be the sowing rate. Whatever seeds you use, sow as thickly as you can, you can never have too much cover crop!
I started digging at it with this beaut tool - it's a great tool for pulling apart compressed copra but not for digging up plants:
I pulled up handsfull of plants and laid them down so the tops were covering the roots of the ones behind them:
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