zeolites and their use in crop production – Dr Z. D. Zartaloudis
zeolites and their use in crop production – Dr Z. D. Zartaloudis
zeolite is a mineral found in volcanic rocks, and possesses interesting properties such as high adsorption capacity and cation exchange capacity. Its crystalline structure is unique in that it cannot be destroyed under any circumstances. It is the only material that can be described as ‘permanently alive’. More specifically, it is a hydrated crystalline aluminosilicate mineral containing alkali cations, with an infinitely open, three-dimensional structure. It is capable of adsorbing and desorbing water and exchanging its structural cations without altering its crystalline structure. Furthermore, zeolites adsorb polar molecules with high selectivity. Consequently, polar CO₂ is preferentially adsorbed by certain zeolites, thereby upgrading methane or natural gas. The ability to bind nitrogen (N₂) from the atmosphere contributes to the enrichment with oxygen (O₂). The selectivity for water (H₂O) adsorption, however, is greater than for any other molecule. Cclinoptilolite has cation exchange selectivity that includes: Cs, Rb, K, NH₄, Ba, Sr, Na, Ca, Fe, Al, Mg and Li. This preference for larger cations, including ammonium (NH₄) (Ames, 1967), has enabled it to be used for the removal of ammonium nitrogen from municipal waste and to extend its use to agricultural and hydroponic applications (Ames, 1967; Mercer et al., 1970).
clinoptilolite and natural chabazite have also been used to extract radioactive caesium and strontium from nuclear waste and radioactive ash. Natural zeolites are used in Japan to improve sandy and clay-deficient soils (Minato, 1968). The use of a volcanic mineral rich in clinoptilolite as a soil improver resulted in significant increases in the yield of wheat, aubergines, apples and carrots (Torri, 1978). The addition of clinoptilolite increased barley yields (Van Bo, 1988) and also increased the yields of potatoes, barley, clover and wheat on Ukrainian sandy loams (sandy loams) (Mazur et al., 1984).
zeolite, when used as a growing medium for chrysanthemums, behaved like a slow-release potash fertiliser, producing the same growth in the plants as that which would result from daily irrigation with a complete Hoagland hydroponic nutrient solution (Hersey et al., 1980). The addition of clinoptilolite with bound ammonium nitrogen in a greenhouse experiment led to a 59 per cent and 53 per cent in radish root weight in soils with medium and low clay content, respectively (Lewis et al., 1984). Adding 10 per cent clino-talc to the sand used in the construction of golf courses reduces nitrate leaching and the increased fertiliser requirements of the turf, without affecting compaction or the quality of the greens (Petrovic, 1990; Huang, 1992). In Italy, natural zeolites have been used as a dusting treatment against aphids on fruit trees (Mumpton, 1999). In Greece, natural clinoptilolite reduced the symptoms of nematode infestation and increased yields and quality in a potato crop in the area of K. Neurokopi, Drama, and in a greenhouse cucumber crop in the Nymphopetra area of Thessaloniki. At high application rates of 15–20 kg per tonne, it demonstrated insect-repellent properties against the olive fruit fly, as well as, at lower doses, against other insects such as the potato leafhopper. It strengthens plants’ natural defences even at low application rates and, when used preventatively, limits the onset or spread of many fungal and bacterial diseases. It exhibits very good synergistic action with various plant protection products. The mechanism behind these effects is not known.
The cultivation of plants in cohesive soils consisting of zeolites, with or without peat, vermiculite and similar materials, is known as zeoponics (zeoponic cultivation). A nutrient-rich zeoponic substrate used for growing plants and rooting cuttings in a greenhouse [achieved greater root development and higher yields of strawberries, tomatoes and peppers without additional fertilisation (Petron et al., 1982). Tomatoes and cucumbers are grown outdoors on a commercial scale in Cuba using a zeolite substrate (Rodríguez, 1983). Using a Bulgarian clinoptilolite product, cabbage and radishes are grown on the Russian space station Mir (Ivanova et al., 1993). Particular attention has been paid to zeolite mixtures of natural zeolites enriched with ammonium or potassium cations and mineral solutions of low-concentration phosphate salts, e.g. apatite (Lai & Eberl, 1986, and Hernandez et al., 1992). Apatite eventually weathers, releasing phosphorus into the soil, and the zeolite releases its exchanged cations (e.g. K or NH₄).
Taking the interaction between zeolite – apatite, NASA has developed a special substrate consisting of clinoptilolite and synthetic apatite, which contains the necessary nutrients for its use as a plant growing medium in space flights. This material could serve as the growing medium for the production of vegetables on all future space missions (Ming, et al., 1995) and in commercial greenhouses. zeolites have been used in agriculture for many years throughout the world, but have recently been recognised as an important and versatile product for use in many agricultural practices. clinoptilolite is the specific type of zeolite used in agriculture.
Source: Dr Z.D. Zartaloudis,
Agrotipos magazine, September 2012 issue