Zeolite/rock phosphate—a novel slow release phosphorus fertiliser for potted plant production

Abstract

A glasshouse study was undertaken to determine if the zeolite mineral clinoptilolite from an Australian deposit in combination with rock phosphate (RP) could significantly enhance the uptake of P by sunflowers. The zeolite/RP combination was intended to act as an exchange-fertiliser, with Ca 2+ exchanging onto the zeolite in response to plant uptake of nutrient cations (NH 4 + or K +) enhancing the dissolution of the RP. A reactive RP (Sechura) and a relatively non-reactive RP (Duchess) were examined. Zeolite was used in Ca 2+-, K +- and NH 4 +-saturated forms at ratios of 3.5:1 and 7:1 with RP; Ca 2+-zeolite was considered the control, with exchange-induced dissolution possible from K +- and NH 4 +-zeolite. The zeolite/RP mixture was applied as a vertical band adjacent to the sunflower seedling. In addition, N was supplied as urea in an effort to determine if RP dissolution resulted from H + release by nitrification. Phosphorus supply from the zeolite/RP system was compared with an available P source (KH 2PO 4). The experiment clearly demonstrated greatly enhanced plant uptake of P from RP when applied in combination with NH 4-zeolite, though the P uptake was lower than that from the soluble P source. The zeolite/RP interaction was much more effective with the reactive RP than the non-reactive material. Within the NH 4 +-zeolite/RP band, root proliferation was greatly increased, as would be expected in an exchange-fertiliser system. The K +-zeolite system did not produce a significantly greater yield than the Ca 2+-zeolite control, probably because adequate K + supply from the basal application reduced uptake within the zeolite/RP band, thus reducing the extent of exchange-induced dissolution. Nevertheless, increased root proliferation within the band was observed, implying that exchange-induced dissolution may also be possible from this system. The zeolite/RP system offers the considerable advantage of P release in response to plant demand and is unique in this regard.