Robert O. Miller

Modification of the ammonium acetate extractant for the determination of exchangeable cations in calcareous soils

Abstract Neutral normal ammonium acetate (NH4C2H3O2) is the extractant predominately used to determine exchangeable cations in agricultural soils. On calcareous soils containing calcium carbonate (CaCO3), this method over estimates exchangeable calcium (Ca). A study was conducted to evaluate five method variables: extractant pH, extraction ratio (soil to extractant), shaking time, shaking vessel, and extractant volume. Modifying these variables, soils formerly utilized in the Western States Proficiency Testing Program were extracted and analyzed for Ca, sodium (Na), magnesium (Mg), and potassium (K). Results indicate that the extraction ratio significantly increased the amount of extractable Ca in soils containing more than 0.5% CaCO3. As the soil:extractant ratio decreased, the amount of measurable Ca increased. The concentration of Ca in noncalcareous soils remained constant in extraction ratios greater than 1:5. Additionally, the pH of the NH4C2H3O2 significantly altered the Ca concentration of the cal...

Proficiency testing and other interactive measures to enhance analytical quality in soil and plant laboratories

Abstract Clients are increasingly seeking enhanced accuracy and precision from soil and plant testing laboratories. Commitment to good laboratory practice is essential, but gains in analytical quality often depend upon inputs from peers through collaborative networks, proficiency programs and laboratory accreditation. Examples of laboratory networks are given, while proficiency programs receive attention with respect to scope, frequency and the statistical assessment of data. Those with a national/regional focus have proliferated with some consolidation warranted. Recent interlaboratory proficiency data from Indonesia and occasional audits of other proficiency programs have been used to reinforce the benefit of non‐parametric statistical procedures for the identification of outlying laboratories, and to suggest greater uniformity in statistical approaches. There is brief mention of formal laboratory accreditation by national providers such as the National Association of Testing Authorities (NATA) in Australia. A disappointing finding was that co‐efficients of variation (CVs) for most soil and plant methods reported in interlaboratory proficiency programs exceed predicted CVs derived from the Horwitz equation. Examples of improving method performance over time are given for two interlaboratory proficiency programs, but grand CVs associated with three successive ASPACs soil proficiency programs remain static at around 16%. The soil and plant laboratory industry must succeed with its efforts to improve analytical performance, as failure may encourage entities outside the industry to intervene.

Estimating soil potassium availability for processing tomato production

Alternative techniques to evaluate soil potassium (K) availability for processing tomato production were compared to the standard ammonium acetate extraction procedure. Ammonium acetate exchangeable K (Kex), solution-phase K (Ksol), and K fixation potential (Kfp) were evaluated on soils from 40 California fields in which processing tomatoes were grown in 1996–98, and on soils from six K fertilization trials conducted in 1997–98. Ksol was determined in the supernatant of 1:10 mixtures (w/v) of soil and 0.01 M CaCl2, either extracted after an initial 30-minute shaking, or after 7 days of incubation at 25°C. Kfp was estimated by enriching dry soil with 1.0 cmol K kg−1 as aqueous KNO3, air-drying, then either extracting immediately with 1 M NH4Cl or after a 7-day incubation in 0.01 M CaCl2 solution. In all tomato fields, the determinate cultivars ‘Halley’ or ‘Heinz 8892’ were grown. Crop K status was evaluated at full bloom growth stage by K concentration in whole leaves, and at harvest by K concentration in fruit dry mass, total fruit K content (kg ha−1), and the incidence of yellow shoulder (YS, a fruit color disorder affected by soil K availability). Kex ranged from 0.17 to 1.33 cmol kg−1, leaf K from 18 to 43 g kg−1, and fruit K from 26 to 70 g kg−1. Ksol and Kfp were highly correlated with Kex (r=0.94 and 0.86, respectively). The Ksol and Kfp techniques utilizing K measurement after the initial shaking/extraction step were highly correlated with results from the procedures utilizing a 7-day incubation period (r=0.99 and 0.98 for Ksol and Kfp, respectively). Kex was more highly correlated with plant K status than either Ksol or Kfp, but correlations ranged from only −0.35 (for YS incidence) to 0.57 (for fruit K content). Potassium application reduced YS in 2 of 4 fertilization trials in which the disorder was prevalent, but none of the measures of soil K availability were predictive of either YS incidence, nor of fruit yield response to fertilization.

Development of a North American proficiency testing program for soil and plant analysis

Abstract A proposal for developing a unified proficiency testing program for soil and plant analysis laboratories in the North American region is presented. The proposed North American Proficiency Testing Program (NAPT) will be based on the quarterly submission to participating laboratories of six soil and/or three plant materials for chemical analysis using reference methods of analysis described in the four Regional Soil Work Group publications of NEC‐67, NCR‐13, SERA‐6, and WCC‐103 and methods outlined in Methods Manual for Forest Soil and Plant Analysis, Forestry Canada. Participating laboratories would complete sample analyses for all or any of the specified analytes and provide results to the NAPT program coordinator for statistical evaluation. Upon completion of the quarterly analysis each laboratory will be provided an evaluation of their individual performance on each of the methods listed. Annually the program will provide a report to each participant of the performance of the individual laborat...

Real-Time Soil CO2 Respiration Rate Determination and the Comparison between the Infrared Gas Analyzer and Microrespirometer (MicroRes®) Methods

ABSTRACT Soil carbon dioxide (CO2) respiration is one of the important soil health parameters that provides a general assessment of soil microbial activity and soil quality. Soil respiration rates, however, have not been widely applied in soil testing protocols mainly because the traditional methods are either inconvenient, technically cumbersome or too expensive. Currently, only two methods are available for a true real-time soil respiration rate determination (<2 h): the infrared gas analyzer (IRGA) and the microrespirometer (MR or MicroRes®) methods. We analyzed the real-time soil respiration rates of 20 soil samples from fifteen states after various periods of incubation using the IRGA method and the MR method. The measured soil respiration rates ranged from 0.4 µL CO2/h/g to 9.0 µL CO2/h/g. Both methods show precision in soil respiration determinations (CV = 12.7% and 11.9%, respectively). Comparison of the results between the IRGA and MR methods indicates high degrees of agreement (r2 = 0.914). This study shows that the MR method is a simpler and more cost-effective alternative for real-time soil respiration rate determinations.

Pulverizing Soils for Laboratory Analysis

Soil-testing laboratories utilize a range of grinder types to pulverize soils for laboratory analysis. This study was conducted to evaluate the effects of soil particle diameter and laboratory subsample size on analysis variability on nitrate, Bray 1 extractable phosphorus (P), extractable potassium (K), and soil organic matter (SOM). Four soils collected for the Agricultural Laboratory Proficiency Program were pulverized using four types of commercial grinders and analyzed for particle-size distribution, P, and K. In a second study, soils were pulverized to pass sieves of 2.0, 1.0, and 0.50 mm and subsampled for P, K, and SOM. Results of the commercial grinders indicate a range in mean particle diameters from 0.15 to 0.60 mm, with the lowest for the grinder utilizing a hammer mill design. Sieve-size analysis results indicate that the coarsest 2.0-mm fraction had the largest variability for all soil analyses evaluated. Analyte variability decreased with decreasing sieve size. Mean Bray P, K, and SOM-LOI (Loss-on-Ignition) mean concentrations were not statistically significantly different across the sieve sizes evaluated. Laboratory analysis variability for extractable Bray P increased as subsample size was reduced.