Evaluation of Spatial Variability of Soil Physico-Chemical Characteristics on Rhodic Ferralsol at the Syferkuil Experimental Farm of University of Limpopo, South Africa

<p>Spatial variability among selected soil physical and chemical properties in twelve profiles dug across the research block of the University of Limpopo experimental farm was investigated. The soils were moderately shallow to deep, contain variable textural classes and classified as Rhodic ferralsol. Over 90% of the samples were considered as slightly alkaline based on the water-measured pHvalues but decreased to marginally over 27% when measured in KCl. The electrical conductivity of the soils revealed a generally non-saline field. Bray P1, EC, exchangeable cations, extractable Zn and effective cation exchange capacity contents differed significantly (p &lt; 0.05) with depth while K, Mg, Ca, Mn, organic carbon and ECEC differed significantly (p &lt; 0.05) across profiles. Semi-variograms for the measured variables had low values indicating the existence of considerable level of spatial variability. Spatial dependence among top and subsoil pH, EC, organic carbon, sand, silt clay and bulk density ranged between weak and strong. Results revealed a significant spatial variability of the characterized parameters across the research block because to differences in tillage, cropping pattern and nutrient specific application over the years.</p>

Serpentine affected soils and the formation of magnesium phosphates (struvite)

Baugé, S. M. Y., Lavkulich, L. M. and Schreier, H. E. 2013. Serpentine affected soils and the formation of magnesium phosphates (struvite). Can. J. Soil Sci. 93: 161–172. The Sumas River watershed, located in the intensive agricultural region of the Lower Fraser Valley of British Columbia (Canada), contains serpentine asbestos from a natural landslide. Serpentinic soils have a high Mg to Ca ratio that can affect soil fertility, including soil-solution P relations. The objectives of the study were: (i) to evaluate some common methods of estimating plant available phosphorus in the surface horizons of the serpentine-affected soils and those receiving large quantities of livestock manure, and (ii) to determine if there is evidence for the formation of soluble Mg phosphates, e.g., struvite, a meta-stable P phase in these soils. Seven soil nutrient extractants were used to determine major and minor elemental concentrations. Acid ammonium oxalate, 1 M HCl and Bray P1 extractions were most effective for measuring available phosphorus in these soils. Manure and fertilizer applications appear to favor the formation of Mg-phosphates, and are considered to be more soluble in terms of phosphorus than either calcium-phosphates or aluminum/iron-phosphates. X-ray diffraction, scanning electron microscopy and nuclear magnetic resonance examinations gave positive evidence for the presence of struvite in the soils.

Effect of experimental conditions on phosphorus extracted from estuarine and marine sediments

The effect of the ratio of sediment to extracting solution was determined on the amount of P extracted by the Bray-P1 extractant (0.03 M NH4F in 0.025 M HCl) from 10 estuarine and marine sediments. Phosphorus extracted from the sediments by the Colwell extractant (0.5 M NaHCO3 at pH 8.5) was also determined. Decreasing the ratio of sediment to Bray-P1 extractant from 1 :7 to 1 : 7000 caused a one-hundredfold increase in extractable P. The amount of Bray-P1 extractable P also decreased significantly (P < 0.001) as extraction pH increased, and extraction pH varied between sediments. Sediment CaCO3 content alone could not explain the increase in extracting solution pH (i.e. neutralization of the acid in the extracting solution) that occurred during the extraction period, and the surface area of the CaCO3 may be a factor in determining final extraction pH. Bray-P1 extractable P was not correlated with Colwell extractable P. Because of the effect of the sediments on Bray extractant pH, it is concluded that this extractant is inappropriate for determining the P status of estuarine and marine sediments. The effect of the ratio of sediment to extracting solution on extractable P has implications for determining the P status of suspended sediments. Extra keywords: Bray extractable P, Colwell extractable P

THE BRAY, MEHLICH AND KELOWNA SOIL P TESTS AS AFFECTED BY SOIL CARBONATES

A study was conducted with five soil P tests (Bray P1 (1:10), Bray P1 (1:50), Mehlich II, Kelowna I and Kelowna II) to determine the effect of soil carbonates on postextraction pH and on the correlation between soil and plant P concentration. Alfalfa (Medicago sativa L.) was grown on five calcareous and six noncalcareous soils fertilized at 0 and 90 μg P mL−1 in a growth room experiment. The ability of the extradants to maintain a low pH with calcareous soils was poorest for the Bray P1 (1:10) followed by the Mehlich II, Kelowna I, Kelowna II and Bray P1 (1:50). The Bray P1 (1:10) did not give a statistically significant correlation coefficient between soil and plant P concentration with the calcareous soils, while the other methods did. Key words: Soil testing, calcareous soils, Bray P1, Mehlich II, Kelowna I, Kelowna II

Automated Analysis of Soil Extracts for Phosphorus, Potassium, Calcium, and Magnesium

An automated method is described for determining P in double acid (0.05N HCI + 0.025N H2SO4) and Bray P1 (0.025N HCI + 0.03N NH4F) soil extracts and K, Ca, and Mg in double acid and 1N ammonium acetate soil extracts. Comparisons are made between double acid and Bray P1 soil extraction methods for removal of P from a Freehold sandy loam soil that had been differentially fertilized with P fertilizers. Comparisons are also made between the double acid and ammonium acetate soil extraction methods for removal of K, Ca, and Mg from the same soil that had been differentially fertilized and limed with K fertilizers and pulverized–dolomitic limestone, respectively. Comparisons are made between automated and atomic absorption determinations of K, Ca, and Mg in standard solutions and double acid and ammonium acetate soil extracts. Bray P1 soil extractant removed 30–73% more P than did the double acid soil extractant from Freehold sandy loam soil. Ammonium acetate extractant removed about 25% more K from soil than did the double acid extractant. Double acid soil extractant removed more Ca from the soil than did ammonium acetate extractant, particularly at high soil Ca levels. Greater amounts of Ca were found in both types of soil extracts by the automated than by atomic absorption techniques. Double acid extractant removed more Mg from soil than did ammonium acetate extractant. The 2 instrumentation methods produced similar results for Mg and K analyses of both soil extract types.