フミン酸カリウムとフミン酸：違い、溶解性、およびそれぞれの使用場面

2つの製品、1つの原料、そして初めて購入する人を戸惑わせる価格差。フミン酸カリウムとフミン酸は、同じレオナルダイト鉱脈から採掘されるにもかかわらず、一方は施肥灌漑タンクできれいに溶解するのに対し、もう一方は底に沈んでエミッターを詰まらせてしまいます。 間違った製品を注文してしまうと、土壌栽培用の製品に過剰な代金を支払うか、あるいは使用しているpH環境では決して溶解しなかった「可溶性」製品によって点滴灌漑ラインが故障してしまうのを目の当たりにすることになります。.

決定の決め手となるのは、メリットの一覧ではなく、ある1つの特性です。以下に、2文でまとめた相性評価、仕様表の並列比較、有効腐植質1単位あたりのコストに関する具体例、そして20 MTの注文が港を出荷される前に確認すべき正確なCOAの項目を掲載します。.

フミン酸カリウムとフミン酸：その違いを簡潔に解説

フミン酸カリウムは、水溶性にしたフミン酸のことです。どちらも軟質褐炭であるレオナルダイトから抽出されたフミン物質ですが、フミン酸カリウムは、未処理のフミン酸を水酸化カリウム（KOH）と反応させて得られるフミン酸のカリウム塩です。 この単一の反応によって、購入者が重視するほぼすべての要素、すなわち溶解性、施用方法、カリウム含有量、そしてトン当たりの価格が変化します。.

未精製のフミン酸はアルカリ性条件下でのみ溶解し、土壌中に留まるため、緩効性の土壌改良剤として機能します。フミン酸カリウムは、pHを問わず水に完全に溶解し、点滴灌漑や葉面散布を通じて素早く移動し、それ自体で6～11% K₂Oを含んでいます。 購入者が土壌施肥を行う場合は、通常、フミン酸で十分です。施肥灌漑や葉面散布プログラムを実施する場合は、カリウムフミン酸が必要となります。.

また、粒状、液体、粉末、フレークの購入形態から選択する必要がある場合は、当社のガイドをご覧ください。 粒状・液状・粉末のフミン酸の比較.

フミン酸カリウムはフミン酸と同じものですか？

いいえ。フミン酸カリウムにはフミン酸が含まれていますが、それはカリウムが結合した水溶性の形態です。 フミン酸を原料と考えると、フミン酸カリウムは、カリウムが組み込まれた、精製済みでタンクへの注入が可能なグレードの製品と言えます。フミン酸カリウムの分析証明書（COA）には、フミン酸の含有率とK₂Oの値の両方が記載されているはずですが、未精製のフミン酸の分析証明書にはカリウムの記載はありません。.

フミン酸カリウムとフミン酸の比較概要

以下の表は、これら2つの項目と、発注を決定する特性との対応関係を示したものです。フミン酸カリウムの数値は、当社が公表しているグレード仕様です。ご注文されるSKUのCOA（分析証明書）と照らし合わせて、正確な数値をご確認ください。.

当社の公表済み製品仕様書に基づく参考値です。貨物の手配を行う前に、実際のCOAと照合してください。.

フミン酸とは一体何なのか

フミン酸とは、フミン物質のうち、アルカリ溶液には溶解するが、酸溶液では沈殿する成分のことです。これは単なるマーケティング用語ではなく、 国際腐植物質学会 フミン酸、フルボ酸、およびフミンを分離するためである。その実用上の意義は、「沈殿」という一言に集約される。未処理のフミン酸を中性または酸性のタンクに投入すると、その大部分は溶液中に留まらなくなる。.

商業的には、フミン酸はレオナルダイトから抽出されます。レオナルダイトは風化した褐炭層であり、そのフミン物質含有量は約85%で、泥炭の3～10%をはるかに上回っています。 Rutom Bio社の原級品は、2～4 mmの黒褐色の顆粒として出荷される。これは散布タンクではなく土壌中で作用し、購入者は基肥として、あるいは複合肥料（NPK）に配合する機能性添加剤として使用している。.

石炭由来の原料には、常に注意すべき点があります。レオナルダイトは褐炭であるため、ヒ素、カドミウム、鉛などの重金属については、単に想定するのではなく、必ず検査を行う必要があります。まさにこの点こそが、EUや韓国からの貨物が港で差し止められる原因となっています。重金属の検査項目が含まれていない腐植物酸の分析証明書（COA）は、不完全な書類となります。.

要点： 未精製のフミン酸は、1トンあたりのコストが最も安いフミン質資材ですが、アルカリ性環境でのみ溶解するという特性上、価格の問題以前に使用可能な場所が限定されてしまいます。土壌内での挙動について作物ごとに詳しく知りたい場合は、当社のガイドをご覧ください。 植物用フミン酸 農学について深く掘り下げて解説しています。.

フミン酸カリウムとは一体何なのか

フミン酸カリウムは、未処理のフミン酸を水酸化カリウムと反応させたときに得られる化合物です。KOHがフミン酸分子上の酸性基を中和してカリウム塩を形成し、その塩はpHを問わず水に溶解します。フミン酸の骨格は変化しませんが、その溶解性とカリウム含有量は変化します。.

この反応により、購入者が仕様書に記載できる2つの利点が生まれます。第一に、水溶性が90～100%へと飛躍的に向上するため、この製品はドリップエミッターや葉面散布器を通しても残留物を残さずに流れます。 第二に、この材料はK₂Oとしてカリウムを含有するようになり（グレードによって通常6～11%）、軽度のカリウム源としても機能します。.

グレードによって、輸送方法や取り扱い方法も決まります。フレーク状および水溶性粉末は溶解が最も速く、残留物も最も少ないため、葉面散布やクリーンな施肥において最高価格がつきます。水溶性顆粒は、溶解性を若干犠牲にする代わりに、取り扱いが容易で粉塵も少なく、別途溶解工程を必要とせずに乾燥施肥プログラムに混ぜ合わせることができます。 K₂Oの含有量もグレードによって異なるため、カリウム含有量を基準に選ぶ購入者と、溶解性を基準に選ぶ購入者は、しばしば同じSKUを選ぶことになります。.

Rutom Bio社は、実用範囲の両端をカバーする2種類のフミン酸カリウム製品を販売しています。その potassium humate granule 0-0-6 runs about 41.5% humic acid at 93% solubility with 6% K₂O, and ships as a stable 2–4 mm granule that still dissolves for drip lines. The potassium humate flake 1-0-11 is the top grade at roughly 56.5% humic acid, 98% solubility, and 11% K₂O, in flake or soluble powder form where low insolubles decide the sale.

Point to remember: potassium humate is not a different molecule from humic acid. It is the same humic material engineered to dissolve and to carry potassium, and you pay for both of those refinements.

The Solubility Fork: The One Difference That Decides Everything

Everything that separates these two products branches from a single property: whether it dissolves in the water you’re going to use. Call it the Solubility Fork — the point where one raw material splits into two application worlds. Get this fork right and the rest of the decision falls out of it; get it wrong and no other spec can save the order.

Down one branch sits alkaline-only humic acid. It stays in the soil, releases slowly, and improves structure and cation exchange over a season. It cannot go into a neutral drip line without dropping out of solution, so its whole working life is in the ground.

Down the other branch sits potassium humate. Because the potassiation step made it soluble at any pH, it moves through fertigation and foliar systems, reaches roots and leaves within days, and carries its own potassium along for the ride. Speed and mobility are the payoff for the refining cost.

Can I dissolve humic acid in water?

Only partly, and only if the water is alkaline. Raw humic acid is soluble in alkali but precipitates in neutral or acidic water, so a portion will settle out and clog emitters. If a supplier tells you their raw humic acid is “fully water-soluble,” they are almost certainly describing a potassium or sodium humate, not raw humic acid. Ask which salt, and ask for the solubility figure on the COA.

Molecular weight and hard-water behaviour

The solubility gap has a second consequence that matters in hard-water regions. Humic acid is the larger, higher-molecular-weight fraction of humic substances, which is part of why it drops out of solution so readily; fulvic acid sits at the low end and stays soluble, and potassium humate is refined to behave closer to the soluble end. In practice, potassium humate tolerates hard, mineral-heavy irrigation water where raw humic acid would flocculate and settle. For fertigation on borehole or well water carrying high calcium and magnesium, the soluble potassium salt is the grade that stays in suspension long enough to reach the root zone. This is the anti-hard-water property some suppliers advertise, and it is real, but it belongs to the humate salt, not to raw humic acid.

The fork also explains the price gap that confuses buyers. You are not paying more for potassium humate because it is a better molecule. You are paying for the KOH reaction that made it soluble and for the potassium it now carries. Decision rule: choose the branch by where the product will be applied, not by the headline humic acid percentage.

The Numbers: Solubility, K₂O & Cost per Active Humic

Raw tonnage price is the wrong number to compare these two on. What actually moves through your program is active humic, and the useful way to size an order is active humic per tonne, calculated as humic acid percentage multiplied by (1 minus moisture).

Run the two potassium humate grades through it:

• Granule 0-0-6: 0.415 × (1 − 0.025) ≈ 405 kg active humic per MT
• Flake 1-0-11: 0.565 × (1 − 0.015) ≈ 557 kg active humic per MT

So to cover 10 MT of active humic, you would book roughly 24.7 MT of granule or 18.0 MT of flake. That 6.7 MT difference is freight and duty you either pay or avoid, which is why the flake grade often wins on landed cost even at a higher price per tonne. Plug in your own target and see where the crossover lands for your port.

The comparison against raw humic acid works differently. Raw humic acid can look cheapest per tonne and per kilogram of humic acid, but if your application needs solubility, its active humic is unavailable to a drip line at any price. That is the trap the next section names.

When to Choose Which

Match the product to the application first, and the grade decision becomes simple. The split is not about which is “better” in the abstract; it is about how the buyer’s customers apply it.

The same decision looks different depending on who inside the buyer’s business is asking. A distributor weighs which grades turn over fastest and tie up the least working capital. An agronomist or grower cares about which one their crop and irrigation method can actually use. A purchasing manager watches landed cost per unit of active humic. All three questions point to the same split, but framing the quote for each of them shortens the sale.

For most distributors the honest answer is that they need both on the shelf: a cheap humic acid granule for the soil-application customers and a soluble potassium humate for the drip and foliar customers. The two are complements, not competitors. If you also field questions about the lower-molecular-weight fraction, our フルボ酸肥料 page covers where that fits.

Decision rule: if it goes in a tank, buy potassium humate; if it goes in the ground and price rules, buy raw humic acid.

The Wrong-Form Tax: What the Wrong Choice Costs

The most expensive mistake here is not overpaying by a few dollars a tonne. It is buying the form that does not match the application, a cost we call the Wrong-Form Tax—the price of solubility you bought and can’t use, or the solubility you skipped and now need.

It runs in both directions. Buy raw humic acid for a fertigation customer because it was cheaper per tonne, and the insolubles clog emitters, coat leaves, and generate returns and complaints that erase the saving. Buy the 98%-soluble flake for a broadacre soil customer who tills it into the ground, and you paid a solubility premium the crop never used.

Picture a distributor who books a container of “soluble humate” on price alone, only to find on arrival it is an alkaline-soluble raw grade. Their drip-irrigation customers report clogged lines within a week. The container cannot be sold into the intended market, freight is already spent, and the next order goes to a supplier who quoted the solubility figure up front. The tonnage saving is gone several times over.

Avoiding the tax costs nothing except reading two lines on the COA before you buy: the water-solubility percentage and the test method behind the humic acid number. Field note: a low price with no solubility figure next to it is not a bargain, it is an unpriced risk.

How to Verify Quality on the COA

A humate COA is only useful if you know which lines to read, and two of them decide whether you are buying evidence or a logo. Before any order, verify these against the per-lot certificate of analysis, not the label or the brochure.

1. Humic acid % with the test method stated. A figure measured one way can read 70% and the same material 45% another way. Confirm the method is identical across the quotes you are comparing, or the percentages are not comparable.
2. Water-solubility and insolubles. For drip and foliar, this is the line that decides the sale. Insolubles clog emitters and coat leaves; ask for the figure, not the word “soluble.”
3. K₂O (for potassium humate). Confirms it is genuinely a potassium salt and not raw humic acid relabelled. No K₂O line means no potassium.
4. Heavy metals (As, Cd, Pb, Hg). Leonardite is brown coal, so confirm the cadmium result against Regulation (EU) 2019/1009 limits before an EU-bound booking.
5. Source and grade. Lignite versus high-grade leonardite changes both the humic acid yield and the heavy-metal profile.

Is potassium humate organic?

It depends on the certifier and the specific product, not on the word alone. Potassium humate is derived from leonardite, a natural mineral deposit, and many grades are accepted for organic production, but the KOH reaction is a manufacturing step some standards scrutinise. Ask for the organic certificate that lists your exact SKU in scope, with certificate number and validity, rather than a logo on the page.

Key takeaway: the certificate proves eligibility and process; only the per-lot COA proves the material in your container.

Reading a Humate Quote: RFQ Red Flags

Comparing two humate quotes side by side only works if they describe the same thing, and they usually don’t. The fastest way to lose money on humic products is to read a lower number as a better deal without checking what sits behind it. A handful of signals separate a quote you can trust from one you can’t.

• A humic acid percentage quoted with no test method. The most common trick: the same lot reads high or low depending on the method, so a method-free percentage is not comparable to anyone else’s.
• The word “soluble” with no figure. For potassium humate, ask for the water-solubility percentage and the insolubles result, not an adjective.
• No K₂O line on a “potassium humate” quote. Either it is raw humic acid relabelled, or the potassium is too low to state.
• No per-lot COA on offer, only a generic spec sheet. A spec sheet is a claim about the product line; the COA is evidence about your container.
• An organic or ISO logo with no certificate listing the SKU and number. A logo is not a scoped certificate.

Line the quotes up on identical humic acid method, solubility figure, K₂O, and heavy-metal panel, and the real price comparison appears. Often the cheaper headline turns out to be the more expensive tonne once insolubles and returns are counted. Decision rule: normalise the quotes to the same COA lines before you compare price, never the other way around.

Sourcing Notes: Grades, Packaging & HS Classification

Once the form is settled, the sourcing questions are the same for both products, with one added line for potassium humate. Grade, packaging, and customs classification are where a clean quote separates a real supplier from a trader.

Both humic acid and potassium humate are commonly declared under HS heading 3101 (animal or vegetable fertilizers), though depending on product form and destination the classification can shift to 3105 or 3824, and duty follows the code. We state the code we declare on export; your customs broker confirms the import rate. Packaging typically runs 25 kg bags on pallets up to full-container loads, with private-label and custom blends available on request.

The full grade matrix, three-tier specifications, and landed-cost detail live on our フミン酸肥料 sourcing page, which is the place to compare grades before you send a spec. For a grower-facing customer who wants the raw soil grade, the humic acid granule SKU is the volume option.

Outlook: Why Solubility Keeps Winning Shelf Space

Demand is shifting toward the soluble grades, and the reason is structural, not seasonal. As drip irrigation and fertigation spread across high-value horticulture in the Middle East, Southeast Asia, and Latin America, the applications that raw humic acid cannot serve are the ones growing fastest. Water-soluble potassium humate rides that shift; a soil-only granule does not.

That does not retire raw humic acid. Broadacre and compound-blend demand keeps the cheap granule moving in volume. But a distributor building a humate line for the next few years is stocking more soluble grade and less raw material than they would have five years ago. Size the soluble side of your inventory to where the irrigation is going, not where it has been.

The Buyer’s Bottom Line

• Potassium humate is humic acid made water-soluble by a KOH reaction, with 6–11% K₂O added. Same backbone, different solubility and potassium.
• Decide by application: soil and blending, buy raw humic acid; drip, fertigation, or foliar, buy potassium humate.
• Compare on active humic per tonne, not raw price. Solubility and potassium are what you are paying the premium for.
• Verify two COA lines before every order: humic acid % with test method, and water-solubility with insolubles.
• Most distributors need both grades on the shelf, priced to the two customer types.

よくある質問

Which is better, potassium humate or humic acid?

Neither is better in the abstract; they serve different applications. Potassium humate wins wherever the product goes into water, such as drip, fertigation, and foliar, because it dissolves fully and adds potassium. Raw humic acid wins on price for soil base dressing and NPK blending where solubility is not needed. Choose by where your customer applies it.

Can I use potassium humate and humic acid together?

Yes, and many programs do. Growers often apply raw humic acid to the soil to build structure over the season and use soluble potassium humate through the drip line or as a foliar spray for fast uptake. They target different jobs, so combining them is common rather than redundant.

What is the humic acid percentage in potassium humate?

It depends on grade. Our potassium humate runs from about 41.5% humic acid in the 0-0-6 granule to about 56.5% in the 1-0-11 flake, with water solubility of 93% and 98% respectively. Always confirm the figure and the test method on the per-lot COA, since a humic acid percentage without its method is not comparable across suppliers.

Does potassium humate dissolve in hard water?

Yes. Potassium humate is soluble across the pH range and handles hard water far better than raw humic acid, which is why it suits fertigation on variable water supplies. For foliar and drip programs on hard water, confirm the insolubles figure on the COA so nothing settles in the tank or clogs emitters.

What HS code is potassium humate exported under?

Potassium humate and humic acid are commonly declared under HS heading 3101, though depending on product form and destination, the classification can move to 3105 or 3824, and duty follows the code. We tell you the code we declare on export; confirm the import classification and duty rate with your customs broker before you commit freight.

Is sodium humate the same as potassium humate?

No. Both are water-soluble humate salts, but sodium humate carries sodium instead of potassium, which makes it cheaper and fine for many industrial or non-agricultural uses. For fertilizer, potassium humate is preferred because it adds useful K₂O and avoids loading sodium into the soil, where it can build up and harm structure on repeated use. Specify potassium humate for crops unless a buyer has a specific reason for the sodium grade.

関連記事

• Humic Acid Fertilizer: Supplier, Grades & Bulk Sourcing, the money page—use this when you’re ready to compare grades and request a quote.
• 植物のためのフミン酸, the agronomy side—use this when the question is how humic acid behaves in soil, crop by crop.
• フルボ酸肥料, the lower-molecular-weight fraction—use this when a customer asks about fulvic instead of humic.

Sourcing Potassium Humate or Humic Acid for Your Market?

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このガイドについて

Reviewed by the Rutom Bio Technical Supply Desk. Last updated 2026-07-20. The potassium humate and humic acid grade specifications cited here are our own published product data; the chemistry and solubility definitions are sourced below. We manufacture both grades, which is why this comparison leads with the sourcing and COA detail that agronomy-only pages leave out. Figures for humic acid percentage and moisture are typical published values; confirm the exact numbers against the per-lot COA for the SKU you order.

参考文献・出典

1. What Are Humic Substances? — International Humic Substances Society (definition of humic acid, fulvic acid, and humin by pH solubility).
2. Regulation (EU) 2019/1009 — European Union fertilizing products regulation (heavy-metal and cadmium limits).
3. Rutom Bio published product specifications—potassium humate granule 0-0-6 and flake 1-0-11 grade data.