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Growth and nutrient uptake of wheat in clinoptilolite-phosphate rock substrates

Allen, E.R., Ming, D.W., Hossner, L.R., Henninger, D.L., Galindo, C.
Agronomy journal 1995 v.87 no.6 pp. 1052-1059
Triticum aestivum, soilless culture, zeolites, rock phosphate, mixtures, plant nutrition, nitrogen, phosphorus, potassium, calcium, nutrient uptake, dry matter accumulation, sand, exchangeable cations, cation exchange capacity, particle size, chemical constituents of plants, ammonium compounds
Mixtures of zeolite and phosphate rock react to release cations and anions into soil solution through dissolution and ion exchange. These mixtures have the potential to serve as slow-release sources of nutrients in synthetic soils. The term zeoponics has been used to describe such systems. Research was conducted to monitor dry matter production and nutrient uptake of wheat (Triticum aestivum L.) in a zeoponic system containing phosphate rock and NH4- and K-saturated zeolite. The objective was to evaluate the ability of zeolite and phosphate rock to provide a balanced supply of N, P, K, and Ca for plant growth. Two zeolite samples (San Miguel and Wyoming clinoptilolite) and two phosphate rock samples (North Carolina and Tennessee phosphate rock) were combined factorially to form four zeoponic mixtures. A series of synthetic soils was formed by combining selected rates of each zeoponic mixture with acid-washed quartz sand. Zeoponic rates (ZR) were 1, 5, 10, 25, 50, 75, and 100% (v/v) of the synthetic soil. Pots were placed in a growth chamber after planting, and plants were harvested every 45 d for a 225-d period. Foliar spray supplied essential nutrients other than N, P, K, and Ca. High yields of wheat dry matter were produced through several cuttings when at least 25% of the synthetic soil was comprised of the zeoponic mixture and when the zeoponic mixture contained a high-reactivity phosphate rock (North Carolina). Tissue analyses suggested that K, and to a lesser extent N, limited wheat growth when ZR less than or equal to 10%. Calcium limited wheat growth at ZR > 10% when a low-reactivity phosphate rock (Tennessee) was used, but not when a high-reactivity phosphate rock (North Carolina) was used. Properly formulated zeoponic mixtures of San Miguel or Wyoming clinoptilolite and North Carolina phosphate rock are capable of supplying sufficient levels of N, P, K, and Ca for intensive growth of wheat.