Cardboard layering deep compost mulch for weed suppression, soil health, and profitability

Our goal was to evaluate the ability of cardboard layering and deep-mulch (CLDCM) to help improve the sustainability and profitability of a small diversified farming operation. Previous SARE grant funding recipients have conducted research on the efficacy of this practice, but the collected data has been predominantly qualitative; this project looked to provide additional quantitative, or measurable data to add to the body of knowledge that fits underneath the no-till umbrella. To achieve this goal three research objectives were addressed during the project period.

Study design: The study took place on eight vegetable production beds, each 30 inches by 100ft. Each bed was randomly assigned as either a test bed with the CLDCM treatment or a control bed using tillage and other traditional practices used by Sweet Hollow Farm. Each bed was treated as one replication, with four replications of each of the two treatments. Measurements of weed density, labor inputs, yields, and soil health were composited across each bed and averaged across the four replications.  Additionally, soil samples were collected at Foraging Farms from four replicated CLDCM beds at the end of the study. Soil type is similar to Sweet Hollow farm so this allowed analyses of affects after seven years of the no-till treatment. With four replications we were able to analyze  the variability of measurements. Brian Maisenbacher with Earthgrower assisted with statistical analyses of the data.

Test Production Bed: Four test beds (30in. by 100ft.) consisting of native soil overlaid with cardboard and compost were prepared in the spring of 2022. To build beds, blank cardboard slip sheets measuring 40in.x 48in. were laid with at least 1ft. overlapping, and then covered with 4-6in. of compost. The compost is an organic commercial mix from Mountain West Products. Pathways were mulched with 4in. of woodchips. Beds and pathways were covered with 4' rows of landscape cloth. Total preparation time for this was 25 hours to lay cardboard and compost and then an additional 2.5 hours to lay weed fabric and drip lines. Planting took 8 hours.

Control Production Bed: Four control beds (30in. by 100ft) consisting of tilled native soil was shaped into beds. Beds and pathways were covered with 4' rows of landscape cloth. Preparation time was 1/2 hour of tractor work along with 2.5 hours to lay drip lines and cover with landscape fabric. It took 4 hours to plant.

In the first year, both control and test beds were transplanted with winter squash. In the test beds, the crops needed a small hole, or dibble, through the cardboard so they can reach the native soil. In the control beds, the same size hole was made and a handful of the same compost will be added. Because the cardboard layer is intended to act as a solid weed suppression, root crops and direct seeded crops are not advised in the first year as they cannot access the native soil and will result in stunted growth. We planted winter squash in each of the 8 beds, with 48in. spacing. They were both irrigated using drip lines on similar schedules and consistent durations throughout all production beds.

Progress Photos

For the second year of the study, the plots were continued in a similar fashion. The control beds we re-tilled and the test beds were left as is. Each of the 4 beds per block were transplanted with 3 rows per bed of onions/shallots out of a 128 cell. Each row of the test and control beds had a different variety planted. Overhead irrigation was used.

wsare onions progress

Metrics:

1.Weed management: Each week the time required to weed the test block and control block was recorded and total labor hours required for each  calculated. In year 1 we opted to cover the beds with landscape fabric. This decision was made because of the severity of our weed problem. It was determined that this crop succession will yield more accurate and repeatable results for like minded farmers. In turn no data was collected. 

In the control bed a stirrup hoe was used to scratch and remove weeds present. In the test bed, the bindweed that penetrates the cardboard was dug up, extracting as much of the root system as possible. Because these tasks required different tooling and overall strategies we  also looked at weed ground cover density. Weed density in each weed management technique was recorded at the end of the second year. *See additional for weed density visual.

2. Soil Health Monitoring: In the transition to the zero-tillage CLDCM approach, we monitored changes in soil health by quantifying chemical, physical, and biological soil properties including soil health indicators recommended in Stott (2019).

We collected soil samples at the beginning of spring 2022 again at the end of the study in the fall 2023. In both the control and the CLDCM treatment, an 18-inch long JMC soil core was inserted 8 inches into the native soil. For the test bed the core was inserted through the compost and cardboard layers and 8 inches into the mineral soil below and sample was taken. Each bed was sampled 10 times to form a composite sample which was placed in a 1-quart sealable plastic freezer bag and immediately placed on ice in a cooler. The samples were transported back with Brian to be analyzed in his lab.

Physical properties  analyzed on soil samples included soil texture, stable aggregate content, and resistance to penetration. Soil texture was measured using a sedimentation test to quantify sand, silt, and clay content. Stable aggregate content was tested using a slake analysis. One TBSP of soil was dropped in a basket with 1cm submerged in water and a timer was to see how long took to dissolve.
Samples sat for 2 minutes before data was collected. The percentae of soil left was logged as the aggregate stability.  Resistance to penetration was measured at the start of the project as well using a depth increment penetrometer pushed as deeply as possible into the soil. This provided baseline data and the same protocols were repeated fall 2023.

Chemical properties were analyzed using a Mehlich-3 extraction method through Logan Labs. The
Logan Labs complete soil test plus extra includes PH, organic matter, base saturation, total exchange
capacity, Melich-3 extractable sulfur, phosphorus, calcium, magnesium, potassium, sodium, boron, iron,
manganese, copper, zinc, aluminum, and estimated nitrogen release. This provided baseline data and the same protocols were repeated in the fall 2023.

Biological soil properties were measured using a microbial density and diversity analysis. Microscopy
techniques and protocols set by Dr. Elaine Ingham were utilized to determine estimations of bacterial
biomass, fungal biomass, actinobacteria, protozoa, amoeba, nematode, and microarthropods. We
also performed in-situ counts of earthworms and other soil mesofauna. This provided baseline data and the same protocols were repeated in the fall 2023.

This sampling protocol resulted in  2 treatments x 4 replications = 8 samples at each sampling period. 8 samples x 2 periods = 16 total soil samples from Sweet Hollow Farm. At Foraging Farm samples were collected at the study’s end, seven years after they deployed CLDCM. The sampling protocol resulted in  2 total samples from Foraging Farms.  *See additional documents for complete testing procedures.

3. Profitability/Yield: We harvested and recorded total weights for the 2022 and 2023 season in both the test and control beds. The recorded weights were analyzed to see trends in productivity for the individual beds as well as to compare levels of productivity between the test and control beds.