Paul F. Vendrell

Salt Concentration and Measurement of Soil pH

The measured value of soil pH depends in part on the laboratory procedures used, such as the soil–solution ratio and soil solution electrolyte composition. One of the most significant factors affecting the measured value of soil pH is the electrolyte concentration of the soil solution. Since electrolyte concentration of agricultural soils can vary greatly during the year and between years, the date of sampling can result in highly variable pH values for samples with the same percentage of base saturation when soil pH is measured in deionized water. For example, we found a different relationship between extractable calcium (Ca) and pH (1:1 in deionized water) for about 18,000 soil samples from the same geographic area taken during winter of 2 years, differing in winter rainfall. On average, samples taken during the wetter year had higher pH for a given value of extractable Ca, consistent with a reduced ionic strength (more leaching) in the wet year. In a comparison of pH in water with pH in 0.01 M calcium chloride (CaCl2) for 1,186 soil samples received from clients, the median difference in pH was 0.67. It is notable that 20% of the samples had a difference of >0.8 and 10% had a difference of >0.9 pH units. Some samples with differences larger than the median may not receive a lime recommendation when needed because of the erroneously high pH reading in water caused by low ionic strength. The stability of pH readings in 0.01 M CaCl2 essentially eliminates this problem.

Implementation of Soil Lime Requirement by a Single‐Addition Titration Method

Abstract Buffers for determining a soils lime requirement (LR) sometimes contain hazardous chemicals. Our objective was to implement a single‐addition titration with calcium hydroxide [Ca(OH)2] to determine the LR of soils. The soil pH buffering capacity is calculated from the rise in pH from a single addition of base. The LR is calculated from the soil pH buffering capacity, the target pH, and initial soil pH. The LR of 531 randomly selected client samples determined by single‐addition titration were slightly higher than by the Adams–Evans (AE) buffer procedure when LRs were less than 1800 lb per acre. The new procedure recommended about 11% less lime than AE at LRs greater than 1800 lb per acre. Independent evaluations of samples that gave the most widely different LR revealed that the single‐addition titration was more accurate and more precise than the AE buffer.

Near-Infrared Reflectance Spectroscopy for the Analysis of Water and Total Nitrogen Contents in Poultry Litter

Near-Infrared Reflectance Spectroscopy (NIRS) offers advantages over gravimetric water content and dry combustion nitrogen determinations that could be significant for routine laboratory operations. Water content in ground and blended poultry litter samples was successfully estimated by NIRS, but total nitrogen predictions differed significantly from measured ones. The failure to predict total nitrogen could be related to the unspecific nature of the relation and to the quality of the data used for calibration. Additionally, a model was established that permits the estimation of water content in poultry litter in its original state from that measured after grinding and blending.

Effects of Storage by Freezing on Concentrations of Molybdate Reactive Phosphorus in Poultry Litter Extracts

Abstract In the laboratory, excessive variability in molybdate reactive phosphorus (MRP) concentrations in water extracts of poultry litter that appeared to be associated with storage by freezing was frequently observed. In one experiment, repeated twice, the effects of a factorial combination of storage temperatures [freezing (−16 to −15°C) or room temperature (21–24°C)] was studied for 60–62 h with poultry litter type (three broiler and one pullet) on MRP concentrations in water extracts. An additional experiment was conducted to compare the effects on phosphorus (P) concentration of a 1 mg P L−1 standard of spiking with 1 mg L−1 of Fe+3 or Al+3 and storage under room temperature or freezing for two and five days. No statistical differences were observed in MRP levels of extracts kept at room temperature measured immediately after the extraction, after 62 h or eight days. Freezing, however, consistently decreased MRP concentrations measured immediately after thawing compared to measurements in extracts kept at room temperature. Reductions ranged from less than 1% to 46%, depending on poultry litter composition, especially total iron (Fe) and aluminum (Al) concentrations. Freezing effects were reversible and after five days MRP concentrations were comparable to those of extracts kept always at room temperature. Spiking with Al+3 did not affect P solubility but spiking with Fe+3 and freezing for five days reduced the MRP concentrations in the P standard when measured immediately or two days after thawing. The results from the P, Fe+3, and Al+3 experiment plus the observation of precipitates containing P and Fe in some of the poultry litter extracts suggested complexing between these elements as a partial explanation of these responses. Organic compounds and Al+3 might also be involved. The solubilization of the floccules upon thawing might be retarded by changes induced by freezing. In consequence, freezing of water extracts of poultry litter can bring about significant, albeit transient, decreases in soluble orthophosphate concentrations.