Relationships between Ambic 1 and Bray 1 extractable phosphorus in some South African arable soils

Abstract

South African analytical laboratories use different extractants for P in soils of which the most important are Bray 1, Ambic 1, Bray 2, Truog and Olsen. The fertilizer industry prefers to use Bray 1 extractions for fertilization recommendations and the ARC-Grain Crops Institute, Ambic 1 extractions for calibration research. Therefore it became necessary to establish relationships between the P extracted by the two methods in specific soils and if possible to relate differences in these relationships to soil properties. Soil samples collected to a depth of 150 mm from phosphorus fertilization trials at 12 localities were used for this study to ensure a large gradient in extractable P. The clay content of the 150 mm topsoil at these localities ranged between 8.4 and 47.0%. More than 3000 soil samples were analyzed for extractable P using both the Ambic 1 and Bray 1 methods. Relationships between Ambic 1 and Bray 1 extractable P for each locality and for 12 localities in total were determined. In addition, multiple and simple regression analyses were carried out to establish relationships between the slopes of Ambic 1 versus Bray 1 relationships and some soil properties of the different localities. Excellent relationships between Ambic 1 and Bray 1 extractable P with R2-values ranging from 92 to 98% have been established at nine localities. At the remaining three localities the R2-values ranged from 75 to 88%. Although the relationship between Ambic 1 and Bray 1 extractable P over all 12 localities was statistically significant with a R2-value of 91 %, the slopes of the different localities differed significantly from each other. Most of the variation between these slopes was attributed to exchangeable calcium (R2 = 80 and 83%), degree of leaching based on clay content (R2 = 80 and 71%), pH(KCI) (R2 = 70 and 69%), effective cation exchange capacity (R2 = 68 and 74%), degree of leaching based on silt-plus-clay content (R2 = 68 and 63%), pH (H 2 0) (R2 = 62 and 68%), Mnoxides (R2 = 60 and 72%) and the exchangeable Fe content (R2 = 60 and 54%) of the soils. It is suggested that at least some of these soil properties should be considered in the development of an universal equation for the conversion of extractable P values from one to the other.

The distribution of inherent phosphorus in fifteen water treatment residues from South Africa

“…The highest AMBIC extractable P concentrations (> 20 mg·kg -1 ) were measured (in decreasing order) in the WTR 12 > 5 > 2 ≈ 9 (Table 2). Typical AMBIC P concentrations for South African soils have been reported to range between 0.3 and 15.3 mg·kg -1 (Schmidt et al, 2004), suggesting that the WTR with high P concentrations may be beneficial from an agronomic perspective and that the land application on P-deficient soils may be of some potential value.…”

Obtaining the parameters required to model labile phosphorus for South African soils

“…In addition, a modified version of the ISFEI (IP) method was used to determine the 'P status' of modal profiles during the compiling of land type maps (Land Type Survey Staff, 1985). Although much work has been done locally and internationally to compare various P extraction methods, much of this work has been restricted to unpublished reports (Schmidt et al, 2004).…”

“…After a study comparing BP1 and AP results from 12 localities in South Africa, Schmidt et al (2004) reported the following relationship using linear regression analysis: BP1 = 1.23 × AP + 3.82…”

Extractable soil phosphorus threshold values for dryland maize on the South African Highveld

“…The equations were then used to derive extractable P concentrations (mg kg-I) or quantities (kg ha-I ) required in the top 150 mm soil for either 90% or 95% grain yield. All of these threshold values were converted to either equivalent Ambic I or Bray I values using the equations of Schmidt et al (2004). The extractable P threshold values for both Ambic I and Bray I were then subjected to simple and mUltiple regression analyses with soil properties.…”

“…Plant Grond 2007, 24(1) Institute for extractable P according to the Ambic I method (Van der Merwe, Johnson, Ras & Schultz, 1981; The Nonaffiliated Soil Analysis Work Committee, 1990), while only some of the samples from each locality were analysed for extractable P according to the Bray I method (Bray & Kurtz, 1945; The Non-affiliated Soil Analysis Work Committee, 1990). However, sufficient samples were analysed with both extractants in order to establish simple regression equations for the conversion of Ambic 1 and Bray I values from one another (Schmidt, Adriaanse & Du Preez, 2004). Other analyses with standard methods (The Non-affiliated Soil Analysis Work Committee, 1990) carried out on these soil samples (114) 373 (63) 582 (98) 684 (116) 477 (81) 727 (123) 925 (156) were particle size distribution (pipette and sieve), pH (M KCI), exchangeable acidity (M KCI), organic C (WalkleyBlack) and exchangeable Ca, Mg, K and Na (Ambic I).…”