Attapulgite or zeolite? A comparison for crops

Two Greek minerals: Grevena & Thrace

Attapulgite (scientifically palygorskite) was identified in 1994 in the Ventzia basin, south-east of Grevena. The deposits occur together with saponite and are considered among the most important in Europe, with indicative reserves of around 6 million tonnes.

Natural zeolite (clinoptilolite) is mined in Thrace, from high-grade deposits.

Both are natural, non-degradable minerals that remain in the soil for years. The difference between them is not “good versus bad”; it is what they hold in the soil and how.

The structural difference: sponge or ion store

Attapulgite is a fibrous clay with needle-like crystals that form a loose network with a large specific surface area (about 150 m²/g). It draws in and holds water by capillary action — it works like a sponge.

Clinoptilolite has a rigid crystal framework with channels of fixed size and negatively charged sites. It also holds water in its pores, but above all it exchanges cations: it stores ammonium (NH₄⁺) and potassium (K⁺) and releases them gradually — it works like a nutrient store.

The measure of this difference is the cation exchange capacity (CEC):

Agriculture: water & soil moisture

Here we must be fair: attapulgite has good data on water retention.

What research shows for attapulgite

In sandy, newly reclaimed fields in north-western China, adding 1,500–6,000 kg/ha of attapulgite powder increased maize yield by 4.9–14.9% and above-ground biomass by 6.1–32.3%. The water-holding capacity of the sandy soil increased, nutrient retention in the top 40 cm improved and leaching to deeper layers decreased. With 20% less fertiliser and 6,000 kg/ha of attapulgite, yield rose by a further 6.6%.

In an experiment on the Loess Plateau, doses of 20 and 40 g of attapulgite per kg of soil improved the water use efficiency of maize, mainly under drought conditions.

In a comparative laboratory study of soil amendments in a loamy sand, attapulgite was the best of the minerals tested (together with bentonite) at retaining moisture: +2.4 percentage points of water versus the control at pF 2.0. The same study also shows the scale, however: the synthetic superabsorbent polymer (SAP) held +18.8 points. Minerals improve the soil — they do not turn it into a reservoir.

What research shows for zeolite

For clinoptilolite, experimental data show an increase in soil water content of up to about 60% and in plant-available water of up to 110%, with the grain size of the material playing an important role.

Agriculture: nutrients & fertilisation — where the difference is decided

A significant share of nitrogen fertiliser never reaches the plant: it is washed out with water or lost as ammonia gas. The same applies to potassium in light soils. This is where cation exchange capacity makes the difference.

Clinoptilolite has a high selectivity for ammonium and potassium. It binds these ions when they are in surplus — after fertilising or irrigating — and releases them gradually as the roots take them up. The fertiliser stays longer in the root zone and less of it reaches the groundwater. In composting and manure management, adding zeolite has reduced ammonia emissions by 15–85%, depending on the dose — the same ammonium-binding mechanism that also works in the soil.

Attapulgite also reduces nutrient leaching, as the study in sandy soils showed — mainly because it keeps more water in the upper layer. With a CEC 5–10 times lower, however, the “ion store” it adds to the soil per kilo of material is correspondingly smaller.

In saline-alkaline soils, research on palygorskite is now moving towards composite products (e.g. with calcium and magnesium sulphates), where the mineral plays a supporting rather than a stand-alone role.

Dose, grain size & soil aeration

A point that is often overlooked: more is not better. A recent study on attapulgite-amended soils on the Loess Plateau found that an excessive dose reduces soil air permeability and hydraulic conductivity, hinders water uptake by the roots and can ultimately affect yield. The researchers conclude that the right dose must be determined by region and soil type.

This makes sense for a fine-grained clay: in large quantities it fills the soil pores. Zeolite does not swell and, in granular form, adds stable grains to the soil structure instead of filling the gaps.

Attapulgite or zeolite in the field: comparison table

Which one for which crop

Feed & litter in brief

Feed

In the EU, any mineral added to feed must be an authorised additive under Regulation (EC) 1831/2003. Clinoptilolite of sedimentary origin has a stand-alone authorisation (1g568) as a binder and anti-caking agent for all animal species, up to 10,000 mg/kg of complete feed, with a positive re-evaluation by EFSA in 2025. Attapulgite has no stand-alone entry — it appears as an accompanying mineral in authorised additives of the sepiolite family, such as sepiolitic clay (1g563). Always ask for the registration number on the label. For binding mycotoxins, the only mineral with explicit authorisation in the EU is bentonite.

Litter, poultry houses & stables

Attapulgite absorbs litter moisture well. Odour, however, comes mainly from the ammonium in urine and manure — an ion, which zeolite binds before it turns into ammonia gas. For litter where both moisture and ammonia matter, zeolite covers both. And litter with zeolite ends up in the field as a nitrogen-richer fertiliser.

In detail: zeolite in livestock farming.

Morphology & safety: what IARC says

The International Agency for Research on Cancer (IARC) evaluated palygorskite in the same Volume 68 (1997) as zeolites. Long fibres (>5 μm) were classified in Group 2B (possibly carcinogenic) and short fibres (<5 μm) in Group 3 (not classifiable). IARC notes that fibre length varies considerably from deposit to deposit. Commercial attapulgites are as a rule short-fibred — there is no cause for alarm, but there is a reason to ask for documentation.

For zeolite, see the guide “Is zeolite carcinogenic?”.

Frequently asked questions