Base Neutralizing Capacity of Agricultural Soils in a Quaternary Landscape of North-East Germany and Its Relationship to Best Management Practices in Lime Requirement Determination

Abstract

Despite being a natural soil-forming process, soil acidification is a major agronomic challenge under humid climate conditions, as soil acidity influences several yield-relevant soil properties. It can be counterbalanced by the regular application of agricultural lime to maintain or re-establish soil fertility and to optimize plant growth and yield. To avoid underdose as well as overdose, lime rates need to be calculated carefully. The lime rate should be determined by the optimum soil pH (target pH) and the response of the soil to lime, which is described by the base neutralizing capacity (BNC). Several methods exist to determine the lime requirement (LR) to raise the soil pH to its optimum. They range from extremely time-consuming equilibration methods, which mimic the natural processes in the soil, to quick tests, which rely on some approximations and are designed to provide farmers with timely and cost-efficient data. Due to the higher analytical efforts, only limited information is available on the real BNC of particular soils. In the present paper, we report the BNC of 420 topsoil samples from Central Europe (north-east Germany), developed on sediments from the last ice age 10,000 years ago under Holocene conditions. These soils are predominantly sandy and low in humus, but they exhibit a huge spatial variability in soil properties on a small scale. The BNC was determined by adding various concentrations of Ca(OH)2 and fitting an exponential model to derive a titration curve for each sample. The coefficients of the BNC titration curve were well correlated with soil properties affecting soil acidity and pH buffer capacity, i.e., pH, soil texture and soil organic matter (SOM). From the BNC model, the LRs (LRBNC) were derived and compared with LRVDLUFA based on the standard protocol in Germany as established by the Association of German Agricultural Analytic and Research Institutes (VDLUFA). The LRBNC and LRVDLUFA correlated well but the LRVDLUFA were generally by approximately one order of magnitude higher. This is partly due to the VDLUFA concept to recommend a maintenance or conservation liming, even though the pH value is in the optimum range, to keep it there until the next lime application during the following rotation. Furthermore, the VDLUFA method was primarily developed from field experiments where natural soil acidification and management practices depressed the effect of lime treatment. The BNC method, on the other hand, is solely based on laboratory analysis with standardized soil samples. This indicates the demand for further research to develop a sound scientific algorithm that complements LRBNC with realistic values of annual Ca2+ removal and acidification by natural processes and N fertilization.

Direct prediction of site-specific lime requirement of arable fields using the base neutralizing capacity and a multi-sensor platform for on-the-go soil mapping

“…It has the form: where α, β and γ are the regression coefficients of the exponential function. For a general description of the BNC data and the soil's pH buffer capacity (pHBC), the reader is referred to Vogel et al (2020). The field-wise characterization of the BNC reveals that the total pH increase over all base additions (δpH total ) strongly varies between the fields having minima of 2.5 (KL60) to 5.1 (KL41) and maxima of 6.2 (PP1392) to 7.6 (KL60) pH units.…”

“…As soils are buffered systems that resist changes in pH, the measurement of pH alone, active acidity, is not sufficient to determine soil LR (Godsey et al, 2007). In contrast, the quantity of bases needed to replace the reserve acidity and increase the pH value to an optimum value to best support a particular crop rotation can be directly quantified by determining the base neutralizing capacity (BNC) of the soil (Blume et al, 2016;Vogel et al, 2020). The BNC is measured in the laboratory by discontinuous titration adding increasing concentrations of a basic solution (e.g.…”

“…To overcome this problem, a more straightforward method might be preferable which directly determines the LR through use of multiple sensor data. Determining the soil BNC is such a direct LR method that determines the effect of lime addition on the pH, individually for each soil sample in order to determine LR from a resulting titration curve (Vogel et al, 2020).…”

Guidelines for precise lime management based on high-resolution soil pH, texture and SOM maps generated from proximal soil sensing data

“…Afterwards, these pH ranges were used to calculate CaO threshold values for over-and under-fertilization using the stepless algorithm described above. For simplicity, the estimates are based on the error (RMSE) of the derived pH map only, as pH has been determined to be the most important soil property for LR estimation in the investigated soils (Vogel et al 2020).…”

Predicting the Lime Demand of Arable Soils from pH Value, Soil Texture and Soil Organic Matter Content

“…Based on the original methods, e.g., to estimate the lime demand of soil [10][11][12][13], lookup table systems were developed as easily applicable tools for farmers to determine the correct amounts of lime [13].…”