Soil and Plant Properties in Cardboard Mulch Prepared No-Till Beds

Soil samples were analyzed at the start and end of the project(Table 1)
Consultants were skeptical about the possibility that this degree of change could occur in only two seasons. The compost used to transplant into, and the layer of earthworm castings found under the mulch (The dark brown material seen under the pulled-back mulch in Figure 2) were also analyzed in order to compare components and try to estimate the contribution of each to the final soil analysis. (Table 2)
Our interpretation is that the end soil analyses (Table 1) reflect a mixing of the compost into the starting soil, along with a substantial amount of earthworm castings, and that this mixing must be the result of earthworm activity since no other tillage was employed. We also believe that the incremental differences in the changes between mulch types corresponds to the initially larger population of worms under cardboard (Table 3). The spatial arrangement of interspersed square plots probably did not permit isolation of earthworm populations under only one type of mulch, so that ultimately, all the soil was "tilled" by the worms to some degree. It is interesting to note that in Sub-Saharan Africa, the Fertility Tree System has a similar basis: instead of spreading prohibitively expensive chemical fertilizers over large acreages, small amounts of organic fertilizers are applied co-locally with interspersed tree plantings. The spreading root system of the tree and the attracted microbial and microfaunal life serve to spread the nutrients into the surrounds of the trees, improving the soil and sustaining other plantings (e.g., : International Journal of Agricultural Sustainability, Sustainable intensification: increasing productivity in African food and agricultural systems , pp. 129-136(8).

The health of the plants in the beds is also protected by the ability of the mulch layers to moderate soil temperature and conserve moisture in the root zone (Table 3,4).

PLANT PROPERTIES

Plant sap monitoring in SARE plot 2010 was limited to small (non-quantitative sample sizes, cardboard mulch plants only):

A balanced level of nutrients in the leaf of the plant will show an ideal pH level of 6.2-6.4., according tot he late agronomist and proponent of Biological Farming, Bruce Taino.

Tomatoes (salad and paste) basil, summer squashes, pumpkins

A lower than ideal pH level will indicate a deficiency in the following minerals: Calcium, Potassium, Sodium or Magnesium.

Lacinato and curly kale, brussel sprouts

A higher than ideal pH level will indicate a deficiency in the following minerals that act in the opposite direction:
Phosphates, Nitrate Nitrogen, Sulfates and trace minerals

(none in this category)

While these tests were qualitative rather than quantitative, they are especially interesting in light of the 2011 plant tissue tests done at the UMASS plant and soil testing lab. These results (Table 5) show that in all the mulches, nutrients are present at satisfactory levels compared to standards, with two exceptions: Calcium and Boron. This is of great interest from the biological farming perspective for two reasons - first, the plant sap pH tests also suggest lack of Ca; and second, it is widely disseminated that Boron is the micronutrient most closely tied to making Calcium available to the plant.

It is also interesting to note that relative levels reflect the same "hierarchy" as all the other measured parameters: cardboard; newsprint; mulch hay. We propose that this is further evidence the the action of the earthworms, which populate the cardboard first and most highly, then newsprint and mulch hay in decreasing order, is responsible for the conversion of the initial soil into the final one, amply supplied with nutrients, and possessing a friability unimaginable at the start of the project. (Figure 7: Soil Appearance at start of project, Figure 8: Soil appearance at end of project)

Earthworms appeared under the cardboard mulch within 48 hours, and continued to populate those areas at twice the rate of newsprint, and three-four times the rate of mulch hay alone for several months. By the end of the season, numbers of earthworms under the newsprint area were roughly equal to the cardboard, but still 2-3x more than mulch hay alone. Earthworms were almost never seen at the surface of the undisturbed beds, and the number of worms below the surface was always in the lowest range.

The quantity of worms under the mulch and in the bed corresponds to the increase in nutrients and micronutrients in those beds as shown in the soil analyses, and to a lesser extent, in the plant tissue samples. This is a combination of the physical mixing of the added compost by the earthworms movement through the beds, and their deposition of castings. It makes sense that the highest increases would occur where there are the highest amount of worms, and that over time, it would all be mixed together as the worms were not subject to a physical barrier between the bed types.
There have been discussions to the effect that the hide glue used to bond the cardboard layers attracts the worms as a protein source. We cannot confirm or deny that, but since we did observe that the equivalent thickness of newsprint also attracted worms more than just a mulch hay layer, that some quality of these mulch types was responsible.

The answer may be in a simple observation - the birds - primarily robins, do not prey on the worms for food through the cardboard, or, in the early part of the season, through the newspaper. The cardboard, since it is laid on top of existing vegetation, now provides a predator-proof cover over an organic matter food source for the worms, it creates a consistently moist environment protected from the sun - all things that are optimal for worm feeding and perhaps more importantly, for mating. As the mulches degraded, there were less worms at the surface but the subsurface numbers remained consistent. It would be really interesting to get a worm specialist to design some controlled experiments in a situation where the subsurface counting would be more rigorous than we could perform.
In addition, the extreme amount of rainfall in 2011, when we attempted to do more rigorous counting, prevented us from maintaining the count squares in fixed locations, and when the soil became saturated so that even new holes would be waterlogged just a few inches below the soil surface, we could not do scientific counting.

The robin observations may have been the most useful part of the exercise, and it would be also useful to consult with a bird behavior specialist to find out more about their hunting preferences.

The use of biological farming assessments was disappointing, in that we could not obtain reference materials to guide our sampling or analysis without incurring large consulting fees that had not been written into the budget. Some of the tests we used (Brix and plant sap pH) are described above. Other testing of the soil was of minor use to us in formulating the results of the project - We submitted soil samples for Formazan testing, a measure of biological activity in the soil, and we had soil bacteria and fungi counts performed by the Soil Food Web laboratories in Oregon, but we were unable to establish a context for the numbers reported.

The most important aspect of this system is that it enables our farm to run with no machinery and the labor of only one full-time farmer. It is worth considering that the method virtually eliminates weeding (Figure 1,2: cardboard mulched commercial kale, pumpkin beds) and minimizes watering (see Results section for data on soil moisture).
What follows is a comparison of logged time for the cardboard method vs estimates of time necessary with more conventional small-farm methods:

In YEAR 1 of the cardboard method, sod is converted into a useable bed by covering with cardboard and then planting into compost-filled holes cut or dibbled through the cardboard layer.
As an example, consider a bed containing tomatoes, stagger spaced at 3' in two rows for 68 plants/bed
Time (one person) logged:
Lay cardboard: 30 mins
Cut and dig holes: 1hr 42 mins
Compost into holes and set seedlings: 1 hr 8 minutes
Cover cardboard w/ mulch hay: 10 mins;
Total time 2hrs 4 mins
It is important to note that -0- time is required for weeding in the cardboard mulched bed.
In comparison a conventional technique requires: (time estimated)
Spring rototill 30mins
Sod breakup 30 mins
Cover bed w/ compost 45 mins
Holes for planting 11 mins
Mulch application 10 mins
Weeding 4x 30 mins/season = 2hrs
Total time 4 hrs 5 mins
We have not estimated equipment costs/maintenance/fuel

YEAR 2
Cardboard method:
total bed prep time 3hrs 11 mins (additional time logged in creating raised bed on top of previous years bed)

YEAR 2
Conventional:
Total time 4hrs 35 mins (additional time for creating raised bed)

YEAR 3:
Cardboard method:
Raised beds in place so time decreases to
Total: 2 hrs 3 mins
Conventional methods:
time remains the same
@4hrs 35 mins

The economic benefits of cardboard mulch, demonstrated by the research results, are:

Free or low cost source of mulch for moisture conservation
Adds organic matter at low/no cost
No weeding (really!) and no bringing up new weed seeds with tillage
No need to wait for weather/field conditions to permit machinery on field, cardboard can be laid at any time under any condition. Additionally, do not have to wait for cover crop or sod to break down, can plant through cardboard at any time.
No equipment/maintenance/fuel costs - and no pollution.
Less time and energy input into watering
Low cost of soil amendments - import over time decreases as opposed to conventional repeat applications yearly. This is due to the "tillage" action of the earthworms, who distribute the added compost throughout the soil in the bed, and add their castings at the same time as they improve drainage and aeration.

The two growing seasons during which this study was conducted presented many challenges. 2010 brought an extremely wet spring, periods of unusually high temperatures in the early part of the season, followed by long very dry periods and unusually high temperatures for longer than usual duration. The research plot experienced severe repeated predation by herbivores destroying most of the crops. This limited the plant-based testing to qualitative results, as we did not have enough plants in reproducible conditions to generate sample sizes for statistically significant data.
2011 was another season of unfavorable conditions for conducting the research. We had planned to focus more on the monitoring of the earthworm population, but the record setting rainfall added complicating factors of earthworm behavior into the mix. The resulting data was useful descriptively, but would not be statistically significant.

• Table 1: Soil Test Results
• Dark brown granular castings under degraded mulch
• Table 2: analysis of other components
• Table 3: Temperature under mulch
• Figure 7: soil at beginning of project
• Cardboard mulched commercial kale beds
• Cardboard mulched commercial pumpkin beds
• Table 4: Soil Moisture under Mulch
• Table 5, plant tissue analyses
• Figure 8: Soil at end of project