NPK Test of Home Compost Output (N=50): What It Shows and What It Doesn’t

One-sentence takeaway​

Across 50 household samples, we see a consistent reality: the output contains nutrients, but it behaves like compost, not a standardized fertilizer.

Why it matters in the kitchen​

If you’re buying Terra 2, you’re not buying “dried crumbs.” You’re buying a material intended to return to the soil. The right question isn’t “How high is the NPK?” but: “Is it usable, stable, and safe to apply the way compost is used?”

What we tested (summary)​

This report summarizes an internal + user-submitted sampling run:

• Sample size: N = 50 finished-output samples
• Sample sources: household outputs under normal use
• What we measured: N, P, K
• Supporting measurements: pH, EC (salinity), moisture, and screening rate

Sampling rules (so the results mean something)​

To reduce noise without turning this into a controlled university study:

1. Only “finished” output (as defined in GK)
2. Screened for large fragments (large pieces are returned to the next cycle)
3. Homogenized subsample for lab submission
4. Feedstock category tag (e.g., plant-heavy / mixed / higher protein / higher oily)
5. Storage note (fresh vs air-cured 24h)

These steps don’t eliminate variability, but they prevent “garbage in, garbage out.”

Results: what we can responsibly say without over-claiming​

1. Nutrients are present; values vary with feedstock (as compost should)

Food scraps are nutrient-bearing. Composting converts them into more stable forms, but it doesn’t erase their chemistry.

Variation is expected based on what went in, leafy greens are not the same as oily leftovers.

2. Compost output is a soil amendment first, not a “guaranteed NPK product”

Unlike bagged fertilizer, compost is valued for:

• organic matter contribution
• microbial activity support
• soil structure improvement (aggregation, water retention)

NPK matters, but it’s not the only (or even primary) reason compost is useful.

3. The main practical risk isn’t “low NPK”, it’s misuse

From an agronomy standpoint, the common failure modes are:

• applying too thick a layer
• using it as the only fertility source for heavy-feeding plants
• ignoring salinity risk when inputs include high salt/oil

That’s why we recommend compost-style use: base dressing or top dressing, not “replace all fertilizer.”

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How to use the output (practical guidance)​

Use it like compost you’d make in the garden:

• As base dressing: mix into soil at a modest ratio (start small)
• As top dressing: apply a thin layer around plants; water in
• Always screen out large pieces: return them to the next cycle
• If you’re unsure: do a simple pot test (control vs amended) over 2–3 weeks

What we did not test (boundaries you should know)​

• We did not claim a single universal NPK level for every home.
• We did not claim it replaces fertilizer programs for demanding crops.
• We did not claim pathogen elimination here (that requires a different protocol).

For definitions, boundaries, and test conditions → Open GK Verification

Methods & boundaries (why compostability standards matter here)​

Composting is aerobic; oxygen supply and process control influence stability. (Reference: US EPA) Temperature windows accelerate decomposition but do not guarantee uniform outcomes by themselves. (Reference: www.chestercountyswa.org)

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