Cultivating Questions
Concerning the Bioextensive Market Garden
by Anne and Eric Nordell of Trout Run, PA
and by Steve Vanek, NEON Research Coordinator
TILLAGE TRIAL IN FIELD 6
RIDGE TILL / NO TILL TRIAL WITH ONIONS
by Steve Vanek, NEON Research Coordinator
- In trying to reduce the amount of tillage in their market garden. Eric and Anne Nordell have developed what they call ridge-till and no-till** in winterkilled cover crops, so that early season crops can be planted with minimal tillage into a dead stand of peas and oats.
- Earlier attempts to simply no-till plant into a flat field of winterkilled cover crop had proved difficult because the soil remained too cool in spring for good early crop growth. The Nordells felt that in a ridged field, the ridge tops should warm up faster and improve crop growth. In ridge till, the top of a ridge is cut off with a modified cultivator sweep, creating a zone of bare soil, while in no-till, a slot is simply ripped into the top of the ridge with a coulter and tooth, for seeding or transplanting the crop. The no-till is also mulched with straw to help conserve moisture.
- A ridge top might also have a problem that in a dry year it would dry out too much and create moisture stress for the crop. Soil moisture and soil temperature were thus two important variables that Eric and Anne wanted help investigating in these systems.
- In collaboration with Eric and Anne, Ron Hoover of Penn State and the NEON case study project were able to measure soil temperature and moisture in Stuttgart onion crops that were planted with these two tillage systems. Our results for 2003 are show here.
SUMMARY OF RESULTS:
- Chart 1: The Ridge-till system had warmer average daily temperatures at 2-inch depth, especially in July as air temperatures climbed. Temperatures may have also been warmer early on, when these would make a difference to early crop growth.
- Chart 2: At least in 2003, the high average temperatures seemed to be more the result of high daily maximums rather than higher temperatures at night.
- Chart 3: Moisture at 12-inch depth. 2003 was a wet year on the whole. During a wet spring and early summer, sufficient rain and the fact that plants were still small meant that there was abundant soil moisture.
- During a mild dry spell in July, when air temperatures were high and the onion plants were large enough to be drawing water from 12 inches, the ridge till system had somewhat drier soil. Drier soil may help to explain why temperatures near the surface were higher in the ridge-till treatment.
- More soil moisture in the no-till treatment may have been the result of the mulch that was applied.
- Chart 4: Yields and bulb size were both good in the two treatments and did not differ in this moderately warm, wet summer. Given the drier soil in the ridge-till during a dry spell, we could speculate that the ridge-till onions might yield lower in a dry year.
**It’s important to note that ridge-till and no-till vary in their meaning considerably. For instance, “no-till” in conventional field crops is usually a system that does away with tillage completely through the use of herbicides and direct planting into residue year after year. At Beech Grove farm the no-till system means that within a single crop season, no tillage has been used to plant or manage the crop, usually onions or garlic.
THE RIDGE-TILL/NO-TILL TRIAL
From A Grower’s Perspective
One of the benefits of being involved in the NEON research project was the opportunity to pursue some of our own research questions. We were particularly interested in getting some “professional help” to setup a trial comparing the difference in soil moisture and temperature between the reduced tillage systems we use for early planted aliums.
NEON research coordinator, Steve Vanek, came to our assistance in the moisture department by installing gypsum block moisture meters at 6” and 12” depths in two rows of Stuttgart cooking onions in Field 6 – one row planted into a clean, ridge-tilled seedbed, and the other no-tilled into the undisturbed cover cropped ridge, then mulched with wheat straw in the pathways.
As Chart #3 clearly points out, the no-till ridges with mulched valleys held more moisture during the only hot, dry spell of the season in 2003. The difference in moisture levels during this relatively brief, if critical, period in the crops growth did not seem to affect yields between the two rows. Indeed, it was difficult to see much difference in crop vigor or health between the two treatments – or across the variable soil textures in Field 6 – at this time.
(The experimental double-row of no-till Stuttgarts in this field was visibly stressed during this short, hot, dry stretch the first part of July, which probably explains why the bulbs in the double-row turned out smaller than single-row Stuttgarts. This side-by-side comparison made us think that increasing plant density without irrigation might really compromise yields in a dry year.)
From a grower’s perspective, the harvest bars in Chart 4 do not tell the whole story about crop profitability. When we pulled the cooking onions the second week of August, the ridge-till Stuttgarts had a lot more soft skins and necks than their no-till counterparts. Our wet weather method of curing storage aliums – topping immediately after pulling the bulbs when the tops are still mostly green, then putting them right in the hoophouse to dry out their necks as quickly as possible – kept the damage from neck rot to a minimum. Still, the sort-out on the no-till Stuttgarts was somewhat better than the ridge-till onions, resulting in the 25% higher income shown in the Labor and Sales Chart for Field 6.
At this point we are not sure if the difference in disease pressure was due to the elevation of the no-till crop up on the ridgetop, or the fact that the singlerow interseeding of vetch in the ridge-till planting had begun to vine over the bulbs during the last week of harvest. Either condition could influence air circulation.
Under exactly the opposite growing conditions in the dry, hot summer of 2002, the onions on the no-till ridges also looked more vigorous during final weeks before harvest. In this case, thrip pressure, not disease, seemed to be the determining factor in crop health and yields. Again, we are not exactly sure how to explain the superior health of the no-till crop, but we suspect it might have something to do with improved moisture retention in the no-till mulched valleys combined with the superior soil quality in the undisturbed cover cropped ridges.
The soil temperature component of the tillage trial came together the end of May in 2002 through completely fortuitous circumstances. When we heard that the On-Farm Research Coordinator for Penn State, Ron Hoover, was setting up a zone-tillage trial on a nearby dairy farm, we made a point of getting a firsthand look at the zone-till planter in action. After explaining our interest in comparing reduced tillage systems on our farm, Ron loaned us six soil temperature loggers. We placed the loggers about two inches deep in rows of ridge-tilled, no-tilled and mulch-tilled onions. (Since we had not anticipated this impromptu trial, the three tillage treatments ended up in two different fields with three different varieties of onions – not exactly a scientific comparison!)
The soil loggers recorded soil temperature every hour for the next eighty days in a microchip about the size of a watch battery. The readout from Ron’s computer showed that average daily temperatures during this hot, dry period were slightly higher in the ridge-till treatment than the mulch till onions, which, in turn, registered a small increase in soil temperature over the no-till ridges. As one would expect, these small differences in soil temperature seemed to correspond to the amount of cover crop residue remaining in the planting zone in each tillage treatment, going from completely clean soil in the ridgetill planting zone to completely undisturbed cover in the no-till ridges.
Looking more closely at the hourly measurements, another difference between the three treatments caught our attention: the daily fluctuation in soil temperature was much more pronounced in the no-till ridges, dropping lower at night than the ridge-till or mulch-till onions, and rising faster during the morning to reach the same high for the day. Given the unseasonably hot weather in 2002, the cooler night-time soil temperatures may have actually been an advantage for the no-till Stuttgarts.
We suspected that the no-till ridges responded more quickly to changes in air temperature simply because the undisturbed ridgetops were surrounded on three sides by the atmosphere. This theory was confounded when we repeated the trial in 2003, placing the soil loggers in the same spots as the NEON moisture meters in the tillage trial in Field 6. As you can see in Chart 2, the soil temperatures in the ridge-tilled planting zone were not only significantly higher than the no-till ridges at times, but fluctuated more widely over the course of the day.
When we asked Ron Hoover his opinion about the seemingly contradictory results, he suggested that soil moisture might be the cause of the difference. He explained that dry soils respond much more quickly to changes in air temperature than wet ground due to the saturated soil holding more latent energy. So in a dry year, like 2002, the no-till ridgetops might respond more quickly to changes in air temperature, but in a wet year, a few inches of elevation might not make much difference. Instead, solar absorption might be the more critical factor in wet conditions. That is, the higher temperatures and fluctuations recorded in the ridge-tilled Stuttgarts in 2003 could be attributed to the clean, dark soil in the ridge-till planting zone absorbing more solar energy than the no-till ridges still partially covered with reflective cover crop residues.
The graphs seem to confirm this supposition by showing that the increase in soil temperatures, and fluctuations, in the ridge-till onions corresponded to the two brief periods of sunshine during the recording period: the last week of April and the first two weeks of July. However, in both 2002 and 2003, all three tillage treatments registered virtually the same soil temperatures when the weather was wet and cloudy, suggesting that the no-till ridges do not slow down soil warming during this kind of weather.
Practically speaking, from a grower’s perspective, moisture seems to be a more important factor than soil temperature for the growth of cool season crops like onions. Based on this assumption, we would cast our vote for the no-till ridges with mulched valleys as the most dependable growing system. The higher yields from the no-till Stuttgarts over the three years we have been experimenting with this minimum-till system seem to support this conclusion.
As for the economics, the increase in yield from the no-till ridge system is almost completely offset by the added expense and labor for mulching the valleys, not to mention the much greater amount of time required for handweeding the undisturbed ridges compared to cultivating the ridge-till onions. Judging from the Labor and Sales Chart, these increased inputs may be justifiable for high income aliums, like the sweet onions and garlic, but may not pay their way for low income cooking onions unless the growing conditions are really marginal.
In order to see if we could improve the return on our investment in mulching and handweeding the no-till ridge system, we experimented with doublecropping the low value Stuttgarts in Field 6 with fall turnips and spinach. After pulling and removing the onions from the field, we made one pass with the cultivator mounted with a single, wide sweep and the minipacker to prepare a seedbed on the top of the undisturbed ridges for direct seeding the turnips and spinach with the walk-behind Planet Jr. No further inputs and labor were necessary other than row covering the turnips to deter flea beetles.
Although the unprotected spinach double-cropped after the no-till Stuttgarts barely made enough growth to warrant picking, the double-cropped turnips, following the experimental double-row of no-till cooking onions and scallions, raised the income from this single no-till ridge about $600, the highest return in Field 6.
From the perspective of maintaining good soil quality, double-cropping the ridges does not make it possible to establish a soil building winter cover crop like the rye and spelt mixture seeded mid-September in the rest of Field 6 following the harvest of the ridge-tilled onions and other crops. On the other hand, we felt that the no-till ridges offered a significant soil quality advantage during the growing season by increasing earthworm activity in the root zone of the onions.
For example, when the weather turned baking hot the beginning of July, the rainpacked soil in the bare planting zone of the ridge-tilled onions crusted and cracked – not exactly the soil condition we like to see for preserving moisture and biological activity. In stark contrast, the nearby no-till ridgetops remained loose and porous due to the beautiful honeycomb like soil structure created by the nightcrawler holes and their castings.
This observation reinforced in our minds the direct connection between residue placement and beneficial earthworm activity. While the worms worked the winterkilled cover crop residues on the no-till ridgetops throughout the wet months of May and June, they soon lost interest in the clean, ridge-tilled planting areas, concentrating their soil aggregating energy on the cover crop residues moved into the pathways during the ridge-tilling process. Had the weather remained hot and dry for the rest of the summer, the difference in soil condition between the ridge-till and no-till planting areas might have had a significant impact on moisture retention and yields.
All in all, the NEON tillage trial leads us to believe that the ridge-tillage system is more sustainable regarding savings in labor and inputs. The mulched no-till ridges, however, seem to provide a better guarantee of good crop growth and soil quality in extreme weather. The ultimate test will be to see how heat loving crops perform in this tillage comparison and whether the results change our cool season conclusions.
SIDE-BY-SIDE (One-After-The-Other) Photos of the TILLAGE TRIAL in Field 6
