The two common philosophies on interpreting soil test results and making fertilizer recommendations are:
- Sufficiency Level of Available Nutrients or (SLAN)/ Buildup and Maintenance
- Basic Cation Saturation Ratio (BCSR)
SLAN/buildup and maintenance is based on university research that demonstrated that sufficient levels or ranges of fertility where maximum yield was obtained, and additional inputs did not enhance yield or produce an economic return. Removal charts, or calculations of fertilizer removed by the crop grown, are incorporated into these philosophies, and based on the measurement of crop removal of essential nutrients in both grain and biomass (stover, plumage, straw, etc.). Fertilizer and use rates are based on a statistical analysis of yield results based on fertilizer additions and economic return and generally, they are based on data subsets from wide geographic areas for specific soil or growing conditions.
The BCSR approach postulates is maintaining an ideal ratio of basic cation (Ca2+, Mg2+, and K+) saturations on the soil exchange sites to maximize crop yields. The practice of adding nutrient amendments to alter the ratios of basic cation saturation in soils is called “soil balancing”. Desired values are calculated based on the Cation Exchange Capacity (CEC) of the soil and the desired or optimum % of saturation that a given cation element takes up on the exchange sites. Rates of fertilization are not based on a yield target or a specific crop to be grown, but by adding enough fertilizer to get to the “ideal” level.
Those that practice BCSR believe that by balancing soil cations you can achieve better weed and insect control, improve soil health and structure, raise crop yields as well as enhance the nutrient value of crops grown for livestock feed. There are also those who believe that once you balance a soil, you no longer need to apply fertilizer. Others believe the soil will make nutrients available and keep them in a balanced state regardless of crop yield or nutrient removal.
What is Soil Balance?
The concept of “soil balance” in plant growth began in the late 1800s. It began with the concept of the “ideal soil” based on Oscar Loew’s 1892 “discovery” that too much calcium or magnesium can be a bad thing. Leow was the first to suggest the presence of an optimal Ca:Mg ratio in soil. However, subsequent research by others showed that there was no evidence that his ratio improved growth, and that in fact, poor yields were a result of calcium deficiencies.
Firman Bear and his coworkers were the first to coin the term “base saturation ratio”. They were trying to reduce luxury consumption of potassium (K) by alfalfa. He proposed the “ideal soil” should consist of 65% Ca, 10% Mg, 5% K, and 20% H on the soil exchange sites (Bear et al., 1945). This translates into a BCSR of 13:2:1.
E.R. Graham (1959) modified these numbers. He then proposed that percent saturations could range from 60% to 85% for Ca, 6% to 12% for Mg, and 2% to 5% for K and if saturations were maintained between these ranges, plant yields would not significantly differ.
William Albrecht, at the University of Missouri, was also working on soil balancing and cation saturation ratios around the same time as Graham. After reviewing his own work and that of Bear and Graham, Albrecht concluded that a balanced soil should have 60% to 75% Ca, 10% to 20% Mg, 2% to 5% K, 10% H, and 5% of other cations to maximize crop yields (Albrecht, 1975). Baker and Amacher (1981) also proposed different ranges for an ideal base saturation; however, the name most associated with soil balance and BCSR is Albrecht. His work has influenced many crop consultants, biological companies, products, or soil testing labs. Most of them will mention Albrecht or the Albrecht method in their philosophy, mission, or business statement.
Around 1991, Neal Kinsey, the latest and arguably most famous champion of BCSR, wrote a book called “Hands on Agronomy” in which defined the ideal ratios as 60%–70% Ca, 10% to 20% Mg, 3% to 5% K, 1% Na, 10% to 15% H, 2% to 4% other cations. Kinsey has gone on to eclipse Albrecht and is now more widely known and influential when it comes to the BCSR system. I feel sorry for Leow, Bear, Graham, Baker and Amacher as they hardly receive any credit or mention regarding the BSCR.
Commonality between those who subscribe to BCSR.
Most if not all labs that subscribe to Albrecht’s teachings use a similar format of soil test and ratio reports. Many still print desired values and pounds (lbs) deficient on the soil report, which are derived from values of ideal soil base saturation of cation elements.
Many of these labs are private, meaning you must belong to or subscribe to their “group” to get access to their soil tests. Many provide training to consultants on how to read their specific soil test results based on the ideal BCSR range and extraction methods of their lab; therefore, consultants will identify heavily with that lab or its mentoring agronomist.
Several of these labs and their consultants will assert that “their lab is the only one using the correct extraction methods or correct reporting methods” for the BCSR philosophy; therefore, most consultants can only read and interpolate the results from the lab that they use and trained them.
Most of the consultants and labs that promote BCSR prefer/promote/assert that you must “zone” soil sample. The zone soil sampling approach is based heavily on soil type, color, and landscape position. They also place a heavy emphasis on “looking at each soil core” before it goes into the composite sample.
BSCR practitioners do not take soil pH into consideration with their lime recommendations, and only base saturation levels of calcium and magnesium is considered. Some even recommend gypsum to amend calcium levels, which has no effect on soil pH. Therefore it is possible to have a soil pH of less than 6.0 and have Ca and Mg base saturation in the “desired value range.” A review of Albrecht’s work indicates that he did not take pH into consideration.
Many who follow the BCSR philosophy pay little attention to actual soil test K values and only focus on the % base saturation of K. This absence of actual K test values can lead to some interesting recommendations.
Soil physical and biological properties are claimed to be enhanced when using the BSCR approach; however, there is no scientific evidence to support this claim.
Several researchers have tried to validate the BCSR philosophy/theory with both greenhouse and field experiments, but they were not able to conclude that an ideal cation saturation ratio existed and found that crop yields were similar across a wide range of ratios.
When using the BCSR philosophy of adding calcium or magnesium limestone to correct ratios or base saturation, yield increases usually resulted from the correction of pH, not in the pursuit of the ideal ratio, when compared to SLAN. In instances where BCSR did increase yields, when compared to SLAN or build/maintenance, BCSR took longer and cost more money per acre.
There is no evidence that a balanced soil will make, provide, or “free up” soil nutrients tied up or held in the soil and there is no evidence that BCSR will increase soil health.
When it comes to soil quality, the aggregate stability of a “balanced soil” is no better than that of an “unbalanced soil”. Balancing the soil is unlikely to affect biological activity beyond the effects of adjusting the pH.
Zone soil sampling based on soil type, color, or landscape position is not superior to grid point sampling. Zone soil sampling can introduce more variability, especially if differences in yield, landscape aspect, and drainage are ignored within zones or if the sample size is too large.
The scientific community mostly disregards the BCSR philosophy/theory; however, some farmers, crop consultants, sustainable ag proponents and commercial soil-testing laboratories still use BCSR to guide their fertilizer recommendations.