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SUMMARYZeolites are hydrated crystalline aluminosilicate minerals of natural occurrence, structured in rigid third dimension net that can be used as slow release plant-nutrient source. The main objective of this study was to evaluate the effects of plant growth substrate under zeolite application, enriched with N, P and K, on dry matter yield and on nutrient contents in consecutive crops of lettuce, tomato, rice, and andropogon grass. The experiment was carried out in a greenhouse, with 3 kg pots with an inert substrate, evaluated in a randomized block design with three replications. Treatments consisted of four types of enrichment of concentrated natural zeolite: concentrated zeolite (Z) only, zeolite + KNO 3 (ZNK), zeolite + K 2 HPO 4 (ZPK) and zeolite + H 3 PO 4 + apatite (ZP), and a control grown in substrate fertilized with a zeolite-free nutrient solution. Four levels of enriched zeolite were tested: 20, 40, 80, and 160 g/pot. Four successive crops were grown on the same substrate in each pot: lettuce, tomato, rice, and andropogon grass. Results indicated that N, P and K enriched zeolite was an adequate slow-release nutrient source for plants. The total dry matter production of above-ground biomass of four successive crops followed a descending order: ZP > ZPK > ZNK > Z.Index terms: stilbite, Lactuca sativa, Lycopersicum esculentum, Oryza sativa, Andropogon gayanus, slow-release fertilizer, growth substrate.(

Dedicated to Prof. Carmine Colella on the occasion of his 70th birthday. a b s t r a c tThis report describes the characterization and application of the Brazilian zeolitic sedimentary rocks as a slow plant-nutrient fertilizer and soil conditioner. The characterization of the head samples showed that it is composed of the zeolite stilbite intertwined with a smectic clay mineral, mixed with quartz. A lowcost quartz separation gravitational technique was used to concentrate the mineral. An enrichment of concentrated natural zeolite was carried out by adding KNO 3 , K 2 HPO 4 and H 3 PO 4 + apatite. These materials were tested with Rangpur lime rootstock and other with four successive crops grown on the same substrate: lettuce, tomato, rice, and Andropogon grass. The results indicated that N, P and K enriched zeolite was an adequate slow-release source of nutrients to plants increasing 20% of crop production and also improving products quality. Other green house and field experiments with concentrated zeolite applied with urea showed 8% of reduction on losses of ammonia volatilization and improving 5% the corn dry matter yield. Concentrated zeolite used as a sand soil amendment also increased at least 10% of soil water retention and 15% of available water capacity.

Nitrogen (N) loss by ammonia (NH 3 ) volatilization is the main factor for poor efficiency of urea fertilizer applied to the soil surface. Losses can be suppressed by addition of zeolite minerals to urea fertilizer. The objective of this study was to evaluate ammonia volatilization from soil and dry-matter yield and nitrogen levels of Italian ryegrass.A greenhouse experiment was carried out with the treatments of urea, urea incorporated into soil, urea + urease inhibitor, urea + zeolite, ammonium nitrate, and unfertilized treatment. Ammonia was captured by a foam absorber with a polytetrafluoroethylene tape. There were few differences between zeolite and urease inhibitor amendments concerning NH 3 volatilization from urea. Results indicate that zeolite minerals have the potential to improve the N-use efficiency and contributed to increasing N uptake. Zeolite and urea mixture reduced 50% the losses by volatilization observed with urea.

This report describes the characterization of a sedimentary occurrence from the Parnaíba Basin, Brazil, containing the zeolite stilbite intertwined with smectitic clay mineral. The head samples from different sites present a wide content range of the zeolitic phase -15% to 50%. The use of simple separation techniques -conventional gravitic treatmentsyields concentrates containing about 67% of the zeolitic component. Assays with the amendments of these concentrates with plant nutrients yield release rates matching those reported for similar commercial products.

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