Okay so now that I have your attention I'll be a little less flashy. Occultation is not really an art and its also not ancient. What the term means is: the state of being hidden from view or lost to notice. In astronomy it is a reference to one celestial body blocking from view another celestial body. In terms of farming the meaning is more simple, it means covering the ground with an object like a tarp such that light cannot penetrate to the objects, the plants, beneath it for a period of time, usually several weeks. This results in the death of the plants and their residues being mostly consumed by worms, fungi and other organisms involved in decomposition. Such that when the covering is removed the amount of work necessary to prepare an area for planting is greatly reduced.
This practice is not new and has been done for many years by many folks involved in organic and sustainable farming. We began to integrate this practice into our operation this year because of several reasons. First we have numerous bed areas that we let lay fallow for two years. These beds were some of the last ones we used mechanical tillage on and were in poor shape. Many had perennial grasses and weeds, the toughest being Canadian Thistle. We needed to bring these beds back into production. Second, our farm is situated on two soil types. Both of which are heavy clay/silt loams that have a tendency to dry slowly in the Spring and have never taken well to mechanical tillage. In our early days we used rototilling to prepare our beds for planting. In just a few years of having to till beds that were not thoroughly dried because we had to get materials planted we created numerous hard-pans in the beds and with the increased aeration in the top 8" it helped burn up our organic material to the point that 4 years ago the soil became almost impossible to work and its productivity dropped significantly. Today, we are in the process of adapting no till practices throughout the farm but we needed an efficient method to knock down the vegetation on these old beds without resorting to mechanical tillage. Enter Occultation.
Pictured above is a typical bed undergoing the process. Each of the beds being treated had to be reshaped to 4' wide. The grass clumps and residue from this process were thrown back on to the bed.
After the bed is reshaped we threw some of excess straw and other organic waste from winter cleanup on top of the bed. The next step is applying the geotextile covering. We buy this material from a nursery supply store in 100' rolls. The textile is slitted to 6' wide. With a standard bed width of 4' the 6' width of tarp gives good coverage on the sides of the bed.
The above picture shows numerous covered beds. We anchor the tarp with soil from the side of the bed every couple of feet down each side. The geotextile fabric doesn't allow much if any light in but does allow a transfer of moisture and air. Thus the soil and organisms underneath get plenty of air and moisture to do their work. In spring when soil biologic activity is just starting to rev up we leave each bed covered a minimum of 4 weeks, but later in the summer when soil biologic activity is at its peak the covering time maybe a week or so less.
Pictured above is the view of a bed once the tarp is removed. The second picture reflects who really did all the tilling!
These beds were broad-forked before covering and as you can see the vast majority of organic materials in the before covering photo has been consumed. Because of the large amount of old sod & slower rotting high carbon organic debris the next step after tarp removal was to rake the beds with a spading fork in the top 3-4" and remove any large clods of sod or other organic debris that didn't easily break apart. Typically we just throw these clods on top of the next bed being prepped for covering. Once we do occultation for several rotations the amount of undigested organic material will decline and we 'll probably be able to skip this step. We then amended the bed with minerals, which for us is primarily ground oyster shell for calcium and CalPhos for both calcium and phosphorus and humates for humic acid.
The last step before planting is to top dress with well rotted compost and lightly fork the mineral and compost into the top 3-4" again using the spading fork. We now have a bed that is ready to plant
The soil pictured above is ready for planting but is still a tad chunky. This will change as the compost, calcium, humates and calphos work on loosening up the soil. The depth of loosened soil is 12-16" which allows for good root growth. A typical rototilled bed would have churned up maybe the top 8-10" leaving a hard-pan below that. What we have also noticed is that the weed pressure is significantly less for the first several weeks after removal of the tarp. Our thought is that the warm moist environment underneath encourage a number of weeds to germinate but they died quickly because of no light and rotted away. By not digging deeply we are lowering the weed seed load overtime by not bringing up buried seed. Mechanical tillage is excellent at bringing up buried weed seeds
We planted our first round of Amazon dianthus in this bed about the end of April and by mid June it looked like this:
There was some weed pressure on the outside of the bed but even after Spring rains the canopy of the dianthus grew fast enough to inhibit much of the weed growth. On another bed which had a huge Canadian Thistle problem we immediately sowed it with buckwheat after occultation to smother any thistle trying to make a come back. It took two weeks for the buckwheat to get to this stage after planting.
Just this last weekend the Buckwheat started to bloom and was ready to incorporate back into the soil. To do this we thoroughly drenched the bed and buckwheat with water and reapplied the tarp over the bed and buckwheat with no additional work. In 4 weeks we'll uncover the bed and will plant one of our last rounds of sunflowers with an under-sowing of sub-clover directly into the bed with no additional work as we expect the succulent buckwheat will have been totally digested. And so it goes, Occultation is a great way to reduce or eliminate mechanical tillage either for your target crop or for incorporating cover crops by letting nature do most of the work.