Management of phosphorus supply to Australian floricultural species

Young plants of Sticherus, waxflower (Chamelaucium) and two Caustis cultivars were grown in a soilless potting medium. The plants were fertilised at seven rates of the soluble monocalcium phosphate (MCP) fertiliser and one rate of the slightly soluble rock phosphate (RP). One group of plants was watered by a non-leaching and a second group of plants watered by a leaching method. Both Caustis cultivars (M63, B84) grown in the potting medium under the non-leaching regime did not show deficiency symptoms at no added P, but they showed P toxicity symptoms at MCP-P application rates > 11 g m-3. The critical P concentration in the shoots associated with a 10% decrease in yield from the maximum was 0.26% for Caustis M63 and 0.33% for Caustis B84. The two Caustis cultivars did not develop P toxicity symptoms or show any decline in shoot dry weight when fertilised with RP under both non-leaching and leaching regimes. Leaching reduced but did not eliminate P toxicity in both Caustis cultivars, although shoot dry weight did not differ significantly between the two watering regimes used. Waxflower grew poorly in the potting medium under the non-leaching regime at no added P or when fertilised with RP but did not develop P toxicity symptoms at any rate of P application as MCP, including the highest rate of 352 g m-3. The waxflower plants grew less well under the leaching than when grown under the non-leaching regime. The critical NaHCO3-extractable P level required for production of 90% relative dry weight of shoots of waxflower was about 46 mg kg-1 under the non-leaching and about 69 mg kg-1 medium under the leaching regime. Under the non-leaching regime the critical NaHCO3-extractable P level for toxicity of Caustis B84 was about 13 mg kg-1 while under the leaching regime this was higher at about 22 mg kg-1. Sticherus plants did not respond significantly to P application as either MCP or RP. However, Sticherus plants grew much better when grown under the leaching than when they were grown under the non-leaching regime. Although leaching conferred some advantages in the growth of Sticherus and in the reduction of P toxicity in Caustis, it also caused a considerable loss of P

Improving Productivity of Mobydick(Asclepias sp) in Mixed Cropping Snallholders Systems In Kenya

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Phosphorus nutrition of Caustis blakei grown with two phosphorus sources of different solubility in two soils of differing phosphorus adsorption capacity

A barrier to the domestication of the phosphorus (P) sensitive Australian species Caustis blakei (Cyperaceae) is the standard production systems used commercially which invariably result in problems associated either with P deficiency or P toxicity. This paper reports on the growth responses of Caustis blakei cv. M63 to applications of fertiliser P as either monocalcium phosphate (MCP) or granulated Guano Gold (R) rock phosphate (RP) in two soils with different capacities to adsorb P. The Caustis M63 plants grown in the two soils did not show P toxicity symptoms when fertilised with RP, but shoot dry weight was 30-60% lower than the control in both soils at the highest rate of MCP-P application (156 kg ha(-1), 184 g m(-3)) and this was associated with visible symptoms of drying of the tips of the ultimate branchlets, in the Mt Cotton soil only. The greatest shoot and root dry weights were achieved by plants grown in the higher P adsorbing Palmwoods soil fertilised with RP at P rates of 30-184 g m(-3). Caustis plants grown in the Palmwoods soil had 2.3 times greater root dry weights than plants grown in the Mt Cotton soil irrespective of the P fertiliser type used. Caustis plants growing in Mt Cotton soil which did not receive P showed significantly lower shoot and root dry weight when compared to plants in the Palmwoods soil, probably due to the low initial bicarbonate-extractable P and the high buffering capacity of the Mt Cotton soil. The P concentration in shoots of Caustis fertilised with MCP at 184 g m(-3) was higher when grown in Mt Cotton soil (0.22%) than in the Palmwoods soil (0.15%). The P concentration was lower in the terminal ultimate branchlets (TUB); 0.15% for the Mt Cotton soil and 0.10% for the Palmwoods soil, suggesting that shoots would provide a more useful indicator of P toxicity than the TUB. It is interesting to speculate as to why plants in the Palmwoods soil showed greater root growth and fewer symptoms of P toxicity. This could be because the Palmwoods soil had the greater P adsorption capacity. These results indicate in ground production of Caustis cut foliage will require careful management of P nutrition and understanding of the complex soil/plant interactions associated with the acquisition of P. (c) 2006 Elsevier B.V. All rights reserved