Cultivating Questions Concerning the Bioextensive Market Garden

by Anne and Eric Nordell of Trout Run, PA

Tailoring The Cover Crop-Tillage Combination To The Planting Window

Finding just the right cover crop-tillage combination for crops planted the last half of June has always been a real challenge in our location. While surface-tilling mature rye and vetch in May works well for fall crops established in July and August, this cover crop-tillage combo does not allow enough time for decomposition and moisture accumulation for end-of-June plantings. Working the rye and vetch a month earlier would provide a more desirable time frame between tilling and planting, but killing this overwintering cover at an immature stage like this often seems futile using a light-weight, two-horse disc. The knee-high live rye bounces back to life after each discing.

Discing a winterkilled cover of oats and Canadian field peas has proven much easier which is why we routinely use this cover crop mix for early spring crops planted in April and May. However, this winterkilled mix decomposes so quickly that by the beginning of June the oat-and-pea residues no longer provide much moisture conserving mulch.

The last two years we have experimented with winterkilled covers that produce a lot more biomass, such as the sorghum-sudangrass mentioned earlier, in the hopes that the resulting mulch of coarse, rot-resistant materials would create better conditions for planting cash crops around the summer solstice without irrigation. An alternative strategy for preparing a moist fertile seedbed for the late June planting window has been to try to figure out a more effective way to shallowly incorporate the overwintering immature rye the end of April.

An answer appeared in the form of Dan Fisher. He paid us a visit five years ago because he was intrigued with our adaptation of ridge-tillage to early season vegetable production. Part of his interest stemmed from the fact that he had helped to develop a ridge-till system for large-scale field crops during his tenure as a biological crop consultant in the Midwest. By contrast to our use of ridge-till as a planting system relying on winterkilled cover crops (see the Spring 2002 SFJ), Dan’s objective for ridge-tilling was the efficient incorporation and decomposition of a live cover crop, like rye, before a heavy feeding crop of corn.

As we understand it, preparation for Dan’s ingenious ridge-tillage method begins right after the previous fall harvest. The idea is to broadcast rye seed over the chopped corn stalks and then rip the ground deeply using a chisel plow equipped with large twisted shovels. The chiseling breaks up compaction caused during combining and incorporates the rye seed at the same time. The reason for using twisted shovels on the chisel plow is they aggressively churn up the earth, throwing the soil and crop residues into low ridges to encourage aerobic decomposition.

Growing the rye on the rough, chiseled ridges provides two important advantages the next spring in terms of sheet composting this overwintering cover crop. First, the ridged soil is noticeably warmer, drier and better aerated than flat ground, creating better conditions for both tillage and decomposition. Just as importantly, the ridged soil surface makes discing more effective by giving the disc blades more purchase than working a smooth field of rye. Dan claimed that knee-high rye would be ready for planting within 2-3 weeks after the first discing!

After Dan’s visit it occurred to us that ridged rye might also make our two-horse disc more efficient at knocking back an immature live cover. Instead of using a hard pulling chisel plow with twisted shovels, we relied on the modified two-row cultivator we call the “ridger” to incorporate the rye seed and form the low ridges.

Based on three year’s experimentation with this technique, we can say that ridged rye definitely makes our lightweight horsedrawn equipment more effective even if several discings are necessary to completely set back the knee-high rye. Our guess is that growing overwintering cover crops on low ridges would also prove to be a mechanical advantage for the tools pulled by a small Farmall tractor like the Super A.

In the following photos we try to detail the steps involved in establishing ridged rye on our farm for the 2002 growing season. We also compare this method for incorporating an overwintering cover crop in April with a winterkilled cover of waist-high sudex, planted in the same field, just to see which of these cover crop-tillage combinations is best suited for that challenging planting window the last half of June.

Ridged Rye Versus Sudex Before Midsummer Lettuce, Beans And Zucchini

1b. Field 3, in the Summer of 2001, was made to order for setting up a comparison between two different cover crop-tillage combinations. Rye on the north and south sides of this fallow field had been incorporated early enough to establish a mix of sudex and Donegal forage soybeans the beginning of August. These heat-loving annuals had already produced a good bit of cover a month later at the time this photo was taken.

In the middle of Field 3 had been our strawberry patch, established the previous spring along with other EARLY planted crops, and surface-tilled right after the last ripe berry was harvested, mid-July of 2001. After shallowly incorporating this heavily mulched perennial crop with the coultervator, disc, ridger and springtooth harrow, this area was now ready for seeding ridged rye.

We have found the best way to establish ridged rye is to incorporate the seed before forming the ridges. We do this the same way we would normally plant a cover crop on a flat field, first broad- casting the rye with a hand cranked cyclone seeder, and then working in the seed with one pass of the springtooth harrow as shown in this photo. Immediately after harrowing in the seed, we…

2b. …rolled the harrowed ground with the cultipacker to re-level and settle the soil. Firming the lightly tilled earth with this type of roller greatly improves germination of the broadcast seed by insuring good seed-to-soil contact and by bringing moisture back up to the surface via capillary action. Based on twenty years of dryland market gardening, we think the cultipacker in combination with lots of surface-tilled residues, is probably the most important tool for establishing crops without irrigation.

3b. We followed the cultipacker with the “ridger.” The three-inch-wide shovels attached to the spring shanks mound the soil and residues into low ridges somewhat approximating the effect of a fast-moving chisel plow with large twisted shovels. No doubt a similar setup could be designed for the Super A by rigging up some kind of toolbar to the back of this small cultivating tractor. We are not sure about the mechanics involved, but we are pretty certain that the horsepower requirements would not be the limiting factor. We say this with confidence because ridging loose soil is one of the earliest jobs for our two-horse team.

4b. Rye greening up on the ridges a couple of weeks later. A visitor checking out the ridged rye suggested that we might have gone about this all backwards! Instead of going to the trouble of creating a serrated field to make our horsedrawn disc more effective at incorporating the rye, why not put serrated blades on the disc? F.Y.I., the 4-5” high ridges spaced 17” apart give our small disc much more purchase than 2” notched blades!

NOTE: If we had not incorporated the cover crops seed before forming the ridges, the ridger would have concentrated most of the rye on the peaks of the ridges, leaving the valleys relatively unprotected.

5b. Another three weeks and the ridges have almost filled in with the overwintering rye. Meanwhile, the sorghum-sudangrass on the north and south sides of Field 3 had grown waist-high with the forage soybeans not far behind. In two months’ time, this heat loving, drought hardy cover crop combo had already produced a lot more coarse biomass than our usual winterkilled mix of oats and field peas.

6b. The sudex mix also died back a lot sooner than our usual oat-pea combination, turning brown with the first hard frost in October. To our surprise, increasing the amount of high lignin biomass with the sudex and soybeans did not prolong the moisture conserving mulch the next spring as we had anticipated. To the contrary, the brittle corn-like stalks allowed a lot more sun and wind to reach the soil than the mat of winterkilled oats and peas. Instead of planting late June crops in the sudex stubble, we ended up using the north and south sides of Field 3 for the early May planting window. That explains why the 2002 Crop Map designates Field 3 as both an EARLY and LATE field, and why we think the sudex-soybean mix might be worth trying in areas with milder winters and wet springs.

7b. Unfortunately, we did not take any photos of discing the ridged rye in Field 3 during the Spring of 2002. But just to give you an idea of the effectiveness of this low-tech, minimum-tillage method, here are a few photos of discing ridged rye in the Contour Strip during the dry spring of 2001. This shot documents the first time over the field when the disc slices and dices the ridges. Very little of the rye is incorporated with the first pass, as documented here, yet the disc blades are cutting much more deeply into the ridgetops than possible on a flat field of immature rye.

8b. Making a second pass in the opposite direction moves the sliced-and-diced rye on the ridgetops into the valleys. A little bit of elevation not only improves the undercutting ability of the disc blades, but makes it possible for this slow moving, horsedrawn implement to bury more of the knee-high topgrowth with soil. This is why we think that serrating the field gives our lightweight disc more of an advantage over the live rye than using serrated blades.

9b. A couple of weeks later we disced the Contour Strip again to kill the remaining rye and more completely incorporate the cover crop residues. We had the opportunity to test out a new disc from the Groffdale Machine Shop for this purpose, thinking this well-engineered implement would make the ultimate minimum-tillage tool for the team. It definitely cut into the soil and residues much better than our modified old disc, but we soon realized it required more weight (such as the bags of rock phosphate temporarily strapped on here) and a hydraulic lift system to really do the job of a primary tillage tool. Otherwise, we were so impressed with the Groffdale disc that we devoted some space at the end of this photo essay to point out the ingenious details of this well-conceived implement.

10b. Back to Field 3 where you can see the midsummer crops of beans and zucchini thriving after ridged rye in 2002. Due to the wet conditions in May and early June, it did take a little more effort to kill the vigorous rye on the ridges than in the dry Spring of 2001. Nevertheless, the technique worked well enough to get the land ready for late June and early July plantings, holding the moisture until we were saved by some end-of-July rains.

The Cornell researcher collecting data on a handful of our crops for NEON, was impressed that the midsummer lettuce already harvested on either side of the zucchini (and interseeded with the single row of buckwheat now blooming in the pathways) produced respectable heads despite receiving only .4” of rain. He also noted that our lettuce samples weighed the same as the other farms in the study which were irrigating as much as possible during this hot, dry period. More surprising to us was that his extrapolations indicated that our single-row lettuce (on a 32” row spacing) yielded as much on a per acre basis as the growers planting their lettuce in multiple-row beds.

As for Jeff Canaan’s questions about selecting a winterkilled cover crop suitable for mild winters and a small cultivating tractor, we wonder if hybridizing the cover crop-tillage combinations trialed in Field 3 might be the answer. At least, when we experimented with planting sudex and soybeans on ridges in the Experimental Patch in preparation for a 2002 interplanting of tomatoes and onions, we were impressed with how early we could begin spring tillage. The soil in the raised ridges covered with coarse corn-like stalks dried out sooner than anywhere else in the market garden. More importantly, our two horsepower disc had absolutely no problem incorporating the ridged winterkilled cover crop in time for the early May onion planting window.