# Inga and fertilizer
### Mulch and Inga alley cropping
Great news. Inga is a system where stripped foliage gives mulch *and* weed abatement. Which is why we love it!
To quote the Inga Foundation, "*the foliage is stripped from the branches and mulched onto the soil surface...The mulch will settle at about 100–150 mm in depth within a few days*." ([Hands 2021](https://doi.org/10.1098/rsos.201204))
Inga works for both because its leaves are *recalcitrant* (slow to rot). So they stick around and suppress weeds, while giving nutrients.
Nitrogen" understates the mechanism. Jeidy says the mulch "provides nitrogen." That's true but misses Hands' central claim. Hands' core finding across 1995, 1998, and 2021 is that Inga's recalcitrant mulch retains and recycles phosphorus in the surface soil layers — which is the actual limiting nutrient in tropical ultisols. N-fixation matters; P-retention is the breakthrough. Pretty much any legume fixes N. Only Inga maintains permanent mulch cover on acid soils for P-cycling. The FAQ answer is technically correct but reads like a generic legume answer, not an Inga answer.
**Jeidy's answer directly contradicts Hands.** Hands is emphatic across all three papers that **mineral supplements are essential**, not optional, in degraded tropical soils:
* **Rock phosphate** at planting: Hands 1998 and 2021 both document that *Inga* alleys without rock-P fail. The San Juan responses to rock-P were "immediate, significant and persistent in every ecosystem component" across the entire 7-year trial.
* **Dolomitic lime + K-Mag (MgSO₄ + K₂SO₄)** for very degraded soils: Hands 2021 §13 describes chlorotic *I. edulis* saplings stuck at 1–1.5 m height that grew to 3–4 m in three months after dolomite/K-Mag application. He calls this "one late lesson from the Cam Projects."
* **Ongoing top-up**: Hands 2021 §12, closing line: "The process can be repeated annually, provided that **minerals extracted in the grain crops are topped up from time-to-time** and that gaps from occasional tree-mortality are refilled."
Hands' position, condensed: *Inga* + rock-P = sustainability; *Inga* alone = eventual failure on degraded latosols.
The distinction Jeidy may be reaching for is **chemical NPK vs. mineral supplements**. Hands does not use synthetic ammonium nitrate, urea, or triple superphosphate — he tested those and rejected them (the soluble P forms leach too rapidly in acid ultisols). He uses **rock phosphate** (slow-release, sorbed onto the mulch layer) and **dolomite/K-Mag** as mineral amendments. These are not "abonos químicos" in the way a farmer means it — they're rock powders, not factory-synthesized fertilizers. So Jeidy is correct that **no synthetic chemical fertilizer** is used. But she's wrong that **no soil amendments are used**.
Three possibilities for what's actually happening in Putumayo:
1. **Soils don't need it.** Amazonian ultisols in Putumayo may be less P-depleted than Honduran sites with a century of slash-and-burn history. Possible — these are virgin or near-virgin forest soils, not 100-years-degraded pasture. Worth a soil test if you don't have one.
2. **It's being done but not in the FAQ.** Selva applies rock-P or dolomite at planting and Jeidy just didn't mention it. Worth checking.
3. **It's missing from the protocol.** Putumayo Inga plantings are not receiving the mineral supplement Hands considers essential. This is a real protocol gap that would compromise long-term performance and survival numbers — exactly what the 6- and 12-month survival bonuses are betting on.
Inga edulis also known as Guamo seeds used for Inga alley cropping
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