Plastic Waste to Fertilizer and the Rupiah: Circular Inputs, Food Security, and Import-Dependency Risk

Rupiah Stability Watch · 2026-09-14

The premise

The rupiah question is not whether plastic can be made morally cleaner by calling it circular. It is narrower: whether waste-derived fertilizer and soil inputs can reduce a real hard-currency exposure in Indonesian agriculture without moving that exposure into imported machines, catalysts, patents, testing services, or failed harvests.

Indonesia has a material fertilizer import line. WITS, using UN Comtrade data, records Indonesia’s 2024 fertilizer imports under HS 31 at about US$1.98 billion, with China, Russia, and Canada the three largest suppliers. Katadata’s report on BPS data gives the same order of magnitude: 7.52 million tonnes of fertilizer imported in 2024, up 40.21 percent by volume year on year, while import value fell 2.65 percent to about US$1.97 billion. That is not a marginal category for a currency-stability ledger.

It also touches the fiscal ledger. ANTARA reported in March 2024 that Indonesia lifted subsidized fertilizer allocation from 4.7 million tonnes to 9.5 million tonnes, with an additional Rp28 trillion bringing the fertilizer subsidy budget to Rp54 trillion, or about US$3.4 billion at the rate cited there. Any substitute input that cannot pass through the subsidy, distribution, and farmer-cost system is not yet a macro stabilizer, even if it works in a laboratory pot.

Rupiah Stability Watch has already treated farm-level automation and bio-inputs as one resilience channel, and waste as a possible operating buffer rather than a moral slogan. This piece extends that frame. Plastic-to-fertilizer belongs on the watchlist, but not as an imminent defense of the rupiah.

What the reported technology actually does

The clearest plastic-to-fertilizer item is the Chiba University work reported by New Atlas and by Chiba itself. It is not a process for dumping mixed plastic waste into soil. It is a designed material system.

The researchers worked with poly(isosorbide carbonate), or PIC, a bio-based plastic made from isosorbide units. PIC could already be chemically converted with aqueous ammonia into isosorbide and urea, but it was too hard and brittle for many practical uses. The new contribution was an isosorbide-based plasticizer that made the material more flexible while preserving its end-of-life conversion pathway. Chiba reports that elongation at break rose from 4.3 percent to 45.2 percent, and that treating the material with aqueous ammonia at 90 degrees Celsius for 24 hours broke it down mainly into isosorbide and urea. New Atlas reports that Arabidopsis thaliana and komatsuna grew as effectively with the resulting fertilizer products as with commercial urea.

That is promising, but the boundary matters. The technology is about a plastic designed in advance to become fertilizer after use. It is not evidence that Indonesia’s existing mixed plastic-waste stream can be safely turned into agricultural input. It also still needs ammonia, heat, reaction vessels, quality control, and collection systems clean enough to keep agricultural input separate from contaminated waste.

The NASA-backed signal is adjacent, not identical. ScienceDaily’s report on the Southern Illinois University work describes engineered yeast converting PET-derived and agricultural-waste-derived compounds into food ingredients for 3D-printed protein-rich cookies. That work came partly from NASA’s Deep Space Food Challenge and uses oxidative hydrothermal dissolution before microbial conversion. It reinforces the larger crossing — waste as feedstock rather than residue — but it is not a fertilizer result and should not be cited as proof that plastic-derived soil inputs are ready for Indonesian farms.

What Indonesia’s external-balance exposure looks like

The fertilizer line has three rupiah-relevant features.

First, it is dollar-priced and supplier-concentrated enough to matter. WITS shows 2024 fertilizer imports of US$1.98 billion, led by China at about US$465 million, Russia at US$451 million, and Canada at US$367 million. Katadata’s BPS-based article reports China at 1.59 million tonnes and US$458.4 million, Russia at 1.38 million tonnes and US$451.5 million, and Canada at 1.25 million tonnes in 2024.

Second, the category is exposed to global fertilizer price shocks. The World Bank’s May 2026 fertilizer market note says its fertilizer price index rose more than 12 percent in 2026Q1 and was projected to rise more than 30 percent in 2026. Urea prices climbed above US$850 per metric tonne in April, up 80 percent since February, while DAP and MOP also rose. The reasons were familiar to an external-balance monitor: energy costs, sulfur and ammonia constraints, Middle East disruption, China export policy, sanctions, and rerouted trade.

Third, fertilizer exposure is tied to food-import pulses. If fertilizer availability or affordability weakens yields, the currency effect does not stop at the fertilizer invoice. It can reappear as rice, wheat, sugar, soybean, or feed imports, and as food-price pressure that forces a fiscal or monetary response. Trading Economics, citing UN Comtrade, lists Indonesia’s 2025 fertilizer imports at US$2.51 billion and cereals at US$3.75 billion. These are not the same channel, but they sit in the same household-food-price stability system.

This is why the issue belongs in a rupiah ledger. It is not because plastic fertilizer is large today. It is because fertilizer imports, subsidy costs, yield stability, and food imports compound through the same external-balance and household-price pathway.

The rupiah transmission chain

A successful waste-derived-input system would help the rupiah only if it does at least one of four things at operating scale:

• reduces kilograms of imported fertilizer or imported raw materials per tonne of crop output;
• stabilizes yield during fertilizer price spikes or supply disruptions;
• lowers farmer cash cost without requiring a larger subsidy bill;
• turns local waste collection and processing into a reliable domestic input chain.

The reverse chain is just as important. A failed input can worsen the rupiah ledger by reducing yield, damaging food-safety trust, triggering additional food imports, and creating cleanup costs. A capital-heavy system can also move the dollar exposure rather than remove it: imported reactors, imported catalysts, proprietary enzymes, imported testing kits, foreign maintenance contracts, foreign IP licenses, and dollar debt for processing plants.

The Chiba process illustrates both sides. It creates urea-containing fertilizer products from a designed polymer, but it needs aqueous ammonia and controlled treatment at 90 degrees Celsius for 24 hours. For Indonesia, the question is not only whether the plant grew in the experiment. It is whether the full system can displace an imported input after counting collection, sorting, heat, ammonia, worker safety, contaminant testing, rejects, and local maintenance.

FAO’s 2021 assessment of agricultural plastics is a useful restraint here. It treats agricultural plastics as products with benefits and trade-offs, and calls for action where products have high potential to harm human or ecosystem health or poor end-of-life management. That is the right posture for plastic-derived fertilizer: a possible circular input, not a permission slip to put poorly characterized residues into soil.

The pilot ledger Indonesia should require

A serious Indonesian pilot should not be judged by a ribbon-cutting or by tonnes of plastic collected. It should be judged by an operating ledger that a farmer, an auditor, and a currency-risk analyst can all read.

The minimum ledger should include:

1. Imported fertilizer avoided: kilograms of urea, DAP, MOP, NPK, sulfur, phosphate, ammonia, or other imported inputs displaced per hectare and per tonne of crop output.
2. Yield stability: yield versus control plots across wet and dry seasons, not only greenhouse or short-cycle trials.
3. Soil and crop safety: tests for microplastics, heavy metals, persistent organic pollutants, plasticizer residues, monomers, solvent residues, pathogen risk where biomass is involved, and nitrogen-release behavior.
4. Input provenance: whether the feedstock is designed PIC-like material, agricultural film, PET, municipal mixed plastic, sludge, or another stream. These are not interchangeable.
5. Energy and chemical balance: heat demand, ammonia demand, water demand, wastewater treatment, and local availability of reagents.
6. Procurement currency: share of capex, enzymes, catalysts, test kits, spare parts, software, licenses, and debt service priced in rupiah versus foreign currency.
7. Farmer cost: delivered price per nutrient unit and per hectare compared with subsidized and unsubsidized fertilizer.
8. Subsidy compatibility: whether the input can be certified, distributed, and audited through existing schemes without weakening controls.
9. Local repairability: whether district-level operators can maintain equipment without imported service teams.
10. Independent verification: third-party agronomic and food-safety results published before scale-up procurement.

This is the same lesson MBG Watch drew from energy-from-waste for kitchens: the generator is not the proof; the readiness record is. For agriculture, the demonstration unit is not the proof. The proof is the input ledger, the soil record, the yield record, and the procurement currency record.

What the evidence supports

The evidence supports three modest claims.

First, designed circular polymers can be made with agricultural end-of-life use in mind. Chiba’s work shows a credible material-design pathway: functionality during use, then chemical conversion into fertilizer-relevant products after use.

Second, waste-as-feedstock research is widening. The NASA-backed SIU work on PET and agricultural waste to microbial food ingredients is not fertilizer evidence, but it strengthens the broader point that waste streams are being treated as controllable carbon feedstocks.

Third, Indonesia has enough fertilizer-import exposure for substitutes to be worth measuring. A US$1.98 billion fertilizer import line in 2024, large subsidy volumes, and volatile global nitrogen/phosphate markets justify pilots that are sober, local, and auditable.

What the evidence does not support

The evidence does not support a claim that plastic-derived fertilizer can defend the rupiah soon.

It does not support a claim that mixed plastic waste is safe for soil. The strongest fertilizer result here comes from a designed bio-based plastic, not from unsorted municipal waste. Indonesia’s plastic-waste problem is real, but an agricultural-input system must be more conservative than a waste-management slogan.

It does not support a claim that circular inputs automatically reduce import dependency. If the domestic product depends on imported reactors, imported ammonia, imported catalysts, imported IP, and foreign testing services, the hard-currency exposure has merely changed address.

It does not support procurement theatre. A pilot that reports tonnes processed but not kilograms of imported fertilizer avoided, yield stability, contaminant tests, and farmer cost is not a food-security pilot. It is a waste-processing demonstration looking for a macroeconomic story.

The least-harm path

Indonesia should treat plastic-to-fertilizer as a measured option in a wider bio-input and fertilizer-resilience portfolio.

The first step is not national procurement. It is a small set of public trials for specific feedstocks: designed biodegradable or bio-based agricultural plastics, clean post-use farm films, and tightly controlled PET or biomass-derived systems where the output is not applied to food crops until safety is clear. Mixed municipal plastic should be excluded from soil-input pilots unless a much stronger separation and contaminant record exists.

The second step is to attach every trial to the operating ledger above. The macro question should be written into the pilot design: how many dollars of fertilizer imports or fertilizer raw materials are actually avoided after counting imported equipment and chemicals?

The third step is to keep the food-price channel central. Inputs that slightly reduce fertilizer imports but raise yield variance are bad rupiah policy. Inputs that reduce imports while maintaining yields, passing contaminant tests, and lowering farmer cost deserve patient scale-up.

The useful stance is neither romance nor dismissal. Plastic-derived fertilizer is a signal that material design may eventually turn waste into a domestic input buffer. For the rupiah, it becomes real only when it survives the ledger: fewer imported nutrients, stable harvests, safe soil, affordable farmers, and no hidden dollar dependency in the machinery behind the claim.

What I’m uncertain about

The largest uncertainty is scalability. The Chiba work is scientifically interesting, but the accessible reporting does not yet show Indonesia-scale cost, lifecycle emissions, ammonia sourcing, or performance across staple-crop systems.

The second uncertainty is safety across feedstocks. A designed PIC system is much easier to reason about than Indonesia’s real plastic waste stream. The more heterogeneous the feedstock, the heavier the testing burden should become.

The third uncertainty is the subsidy interface. Indonesia’s fertilizer system is not only a market; it is also a fiscal and distribution system. A new input that cannot be verified, priced, and distributed cleanly may remain outside the channel where household food-price stability is made.

The fourth uncertainty is whether the import bill falls or migrates. Until pilots publish the procurement currency of reactors, reagents, maintenance, IP, and testing, the rupiah benefit should be treated as unproven.