A comparison between plant response and chemical measurements of the dissolution of reactive phosphate rock in soils of different pH and phosphorus retention

Abstract

Chemical measurements of the dissolution of reactive North Carolina phosphate rock (PR) in a lateritic podzolic soil adjusted to different pH values or amended to different P retention capacities were compared with plant response data. Soil pH adjustment consisted of incubating soil mixed with dilute HCl or solid SrCO3. The P retention capacity was adjusted by adding different amounts of synthetic goethite. Clover was grown as a test crop under glasshouse conditions on soils treated with no P and 800 �g Pg-1 soil as PR. The dissolution of PR, measured as the increase in soil exchangeable Ca (�Ca) at harvest time, increased by 46% for a decrease in soil pH from 5.78 to 4.55. Both dry weight and P content of clover tops showed no response to the greater PR dissolution at low soil pH, although twice as much P was bicarbonate-soluble at pH 4 55 compared with pH 5.78. This increase in bicarbonate-soluble P was only partly due to the greater dissolution of PR. Increasing the goethite content of the soil by 9% resulted in a 107% increase in PR dissolution but induced a 54% decrease in the bicarbonate-soluble P level compared with the control soil and consequently reduced both dry weight yield and P content of clover tops by 19% and 34% respectively.

The effectiveness of Langebaan rock phosphate and superphosphate in two acid, phosphate-deficient soils

“…The significant increases in plant response to superphosphate, following the application of lime to acid soils, suggest that the increase in the effectiveness of PR, relative to superphosphate, with increasing acidity, may in some instances be more a consequence of the inefficient utilization of superphosphate by plants in the presence of phytotoxic concentrations of aluminium, than of enhanced PR dissolution per se. Although favourable responses to PR may still be obtained after liming if the detrimental effects of excessive soil acidity exceed its beneficial effects on PR dissolution (Bennett, Ensminger & Pearson, 1957;Khasawneh & Doll, 1978;Yost et al, 1982;Kanabo & Gilkes, 1987b), the increase in yield tends to be substantially less than that obtained with superphosphate after liming. It is therefore apparent that, to maximize plant utilization of 'available' P and to achieve optimum yields on many acid soils, the soils have to be limed first, but, since this reduces the reactivity of PR, its potential to be a substitute under these conditions may be limited (Van der Paauw, 1965; Barnes & Kamprath, 1975;Juo & Kang, 1979).…”

“…Soils with a large capacity to effectively immobilize P from the soil solution generally promote a more rapid and extensive dissolution of PR than do soils which retain P weakly (Chu et 01., 1962;Chien, Leon, & Tejeda, 1980;Smyth & Sanchez, 1982;Hughes & Gilkes, 1986;Kanabo & Gilkes, 1987a;1987b this, PR effectiveness may be lower in strongly P-fixing soils, owing to the strong retention of the dissolved P against plant uptake (Mackay, Syers, Gregg & Tillman, 1984b;Hammond, Chien & Easterwood, 1986;Kanabo & Gilkes, 1987b). This situation also applies to water-soluble P fertilizers (Mackay et al, 1984b;Hammond et al, 1986) and it is the relative decrease in effectiveness of both sources, rather than the absolute decrease, which is of more interest in agriculture.…”

“…In contrast, phosphate rock (PR) is highly insoluble in water and the driving force for its dissolution is determined to a large extent by the gradient in the activities of phosphate, calcium and hydrogen ions (Khasawneh & Doll, 1978). It has beeq reported that the rate and extent of PR decomposition is greatly enhanced in soils which have a low pH (Chu, Moschler & Thomas, 1962;Anderson, Kussow & Corey, 1985;Kanabo & Gilkes, 1987b;1987c), high levels of reserve acidity (Kanabo & Gilkes, 1987c;Bolland, Gilkes & D'Antuono, 1988a;Bolland & Gilkes, 1990) and low calcium status Mackay, Syers, Tillman & Gregg, 1986). Compared with water-soluble P fertilizers, therefore, PR should be relatively more effective when applied to acid, well-buffered soils than to neutral soils or to soils which have recently been limed (Archer, 1978).…”

Effect of Mycorrhizal Inoculation on Rhizosphere Properties, Phosphorus Uptake and Growth of Pine Seedlings Treated With and Without a Phosphate Rock Fertilizer

“…This high degree of dissolution of BGPR is due to the acidic nature of the soil, the long period of experimental time (10 months) and very small particle size of BGPR used (150-250 µm) (Kanabo and Gilkes, 1988). The high P retention (92%) and low Ca concentration in the Allophanic Soil would also have promoted the enhanced dissolution of BGPR in the soil (Kanabo and Gilkes, 1987;Bolan et al, 1997). Similar to our previous observation on the same type of soil (Liu et al, 2004), little dissolved BGPR-P remained in the easily plant-available resin-P pool (mean 1.3 µg g −1 soil in P-fertilized soils compared to <0.76 µg g −1 soil in P-unfertilized soils), while most of the dissolved BGPR-P were redistributed into the 0.1 M NaOH-P i fraction (around 44%).…”

Influence of rates of reactive phosphate rock and sulphur on potentially available phosphorous in organically managed soils in the south-eastern near-Mediterranean cropping region of Australia

“…For RPR to be effective, soils need to supply sufficient hydrogen ions to dissolve P from RPR enough to match plant demand for P (Ellis et al 1955;Kanabo and Gilkes 1987;Rajan et al 1991). The concentration of hydrogen ions in soil may be increased by biological oxidation of elemental sulphur (S) (Germida and Janzen 1993), so applying S with RPR enhances dissolution of P for plant production (Lipman et al 1916;Kittams and Attoe 1965;Rajan 1981Rajan , 1983Rajan , 2002.…”