Inside the Soil Safety Reports: What Four Independent Lab Studies Actually Measured

If you're considering biodegradable mulch film for your fields, "biodegradable" alone doesn't tell you much. What matters is what the film becomes once it breaks down, and whether that residue does anything to the soil you depend on year after year.

That's the question SoilBond, made by Carbon Nurture, put to an independent lab four separate times. Not synthetic worst-case tests. Not internal claims. Real soil from real test fields, checked by a third-party lab against untreated soil from the same site.

This is a walk-through of what each test measured, how it worked, and what the results showed. All four source reports are available to download in full on our soil safety resource page.

What Is EN 17033, and Why Does It Matter?

EN 17033:2018 is the European standard that defines requirements and test methods for biodegradable mulch films used in agriculture. It's the closest thing the industry has to a shared rulebook for proving a film is safe for soil, rather than just marketed that way.

The standard sets pass or fail thresholds across four types of ecotoxicity testing: plant growth on two different plant types, earthworm survival, and nitrification activity. A film must clear a specific bar on each one, measured against untreated soil, to meet the standard. SoilBond was tested against all four.

Who Ran the Tests?

All four studies were conducted by Normec OWS nv, an independent laboratory in Ghent, Belgium, under OECD Good Laboratory Practice (GLP) principles, the international quality standard used for regulatory and scientific testing. Each report includes a full methodology, raw data tables, and sign-off from an independent Study Director and Quality Assurance reviewer. 

One detail worth noting: the soil used in testing wasn't a synthetic sample spiked with test material in a lab. It was real soil pulled from Carbon Nurture's own test fields, soil that had already absorbed SoilBond's residuals after the film biodegraded, compared directly against untreated soil from the same site.

Test 1: Does the Soil Still Grow Crops? (Barley Growth Test)

Quick answer: Yes. Barley grown in soil containing SoilBond's residue germinated at 106% of the control rate and produced 24 to 25% more plant biomass.

Barley was chosen because it represents monocotyledonous plants, grass, and cereal families. The test followed the OECD Guideline 208 (Terrestrial Plant Test: Seedling Emergence and Seedling Growth), with the modifications required by EN 17033.

Researchers planted 50 barley seeds in each of eight pots, four containing soils with SoilBond residue and four containing untreated control soil. After 10 days, they measured the germination rate and both fresh and dry plant weights.

Results: 

• Germination: 93.0% in test soil versus 87.5% in control soil (106% relative)

• Fresh weight: 6.59g versus 5.27g (125% relative)

• Dry weight: 0.59g versus 0.48g (124% relative)

To pass EN 17033, germination and biomass in the test soil needed to reach at least 90% of the control. SoilBond soil didn't just meet that bar; it exceeded the control outright.

Test 2: Does It Work Across Different Crop Types? (Cress Growth Test)

Quick answer: Yes. Germination and yield in cress both came in at or above 90% of the untreated control, meeting the EN 17033 threshold.

Where barley represents grass, cress represents dicotyledonous plants, the broadleaf family that includes many vegetables and row crops. Testing both plant types checks whether a result holds across different kinds of agriculture, not just one crop family.

The test ran the same way: seeds planted in pots of test soil and control soil, measured for germination and plant weight once the seedlings had been established.

Results: 

• Germination: 75.0% in test soil versus 79.3% in control soil (95% relative)

• Fresh weight: 3.01g versus 3.02g (100% relative)

• Dry weight: 0.20g versus 0.20g (103% relative)

All three measures cleared the required 90% threshold. Combined with the barley results, this confirms the plant-growth finding isn't limited to one type of crop.

Test 3: Does It Harm Life Already in the Soil? (Earthworm Survival Test)

Quick answer: No harm found. 100% of earthworms survived in soil containing SoilBond residue, matching the control group exactly, with body weight remaining within 4% of the untreated soil.

Earthworms are one of the most sensitive indicators of soil toxicity available. If something in the ground is harmful, earthworms tend to show it first, through reduced survival or weight loss. This test followed ISO 11268-1 and ASTM E1676, with EN 17033's modifications.

Ten earthworms were placed in each of several soil-filled jars (test soil, control soil, and a standard artificial soil used to validate the test itself). Survival was checked at 7 and 14 days; body weight was measured at the end.

Results: 

• Survival at 14 days: 100% in both test soil and control soil

• Mean weight of survivors: 96% of the control soil's weight retention

EN 17033 requires the difference in mortality and biomass between test and control soil to stay under 10%. SoilBond soil showed no mortality difference at all, and its weight result was well within that margin.

Test 4: Does It Disrupt the Soil's Nitrogen Cycle? (Nitrification Inhibition Test)

Quick answer: No inhibition was found. Nitrite formation in the test soil measured 85% of the control soil's rate, above the 80% threshold required to pass.

This is the least visible of the four tests, but arguably one of the most important for long-term soil fertility. Nitrification is the process by which soil bacteria convert nitrogen into a form plants can absorb. If a residue disrupts these bacteria, a field can lose fertility gradually, with no obvious sign until yields start to drop.

The test, based on ISO 15685, exposed soil samples to a controlled reaction over 6 hours and measured how much nitrite the soil's ammonium-oxidizing bacteria produced, comparing test soil to control soil.

Nitrite formation in SoilBond-exposed soil reached 85% of the control rate, comfortably above the 80% minimum EN 17033 requires. The soil's natural nitrogen cycle continued largely undisturbed.

What This Means If You're Evaluating Mulch Film

Together, these four reports answer the questions that matter most before a biodegradable film goes into your fields: does it still let things grow, does it harm the organisms already living in the soil, and does it interfere with the soil's own long-term fertility processes.

SoilBond passed all four, tested by an independent lab, against real field soil, using internationally recognized methods. That's a different kind of proof than a marketing claim, and it's the kind of documentation worth asking for from any mulch film manufacturer, not just this one.

Frequently Asked Questions

What is EN 17033? EN 17033:2018 is the European standard defining requirements and test methods for biodegradable mulch films used in agriculture, including ecotoxicity thresholds for plant growth, earthworm survival, and nitrification.

Does "biodegradable" always mean a mulch film is safe for soil? No. Some biodegradable plastics break down into microplastics or leave additive residues behind even after the visible film disappears. Ecotoxicity testing, like the four reports covered here, is how that gets verified rather than assumed.

Who conducted the SoilBond testing? Normec OWS nv, an independent, GLP-compliant laboratory in Ghent, Belgium, with no financial stake in the results.

Can growers read the full reports themselves? Yes. All four reports, covering barley growth, cress growth, earthworm survival, and nitrification, are available to download in full on our soil safety resource page.