Agriculture Reference
In-Depth Information
Box 3.7 The Albrecht System of a Basic Cation Saturation Ratio
The concept of a basic cation saturation ratio (BCSR) postulates that the
exchangeable cations Ca 2+ ,Mg 2+ , K + , and Na + should be present in “ideal”
proportions of a soil's cation exchange capacity to promote optimum plant growth.
After research on a range of crops in the United States, Albrecht (1975) concluded
thattheidealproportionswereCa60%to75%,Mg10%to20%,K2%to5%,
Na 0.5% to 5%, and H 10%, and specific values were placed on the ratios of
Ca-to-Mg,Ca-to-K,andK-to-Mgforoptimumplantnutrition.
What came to be known as the Albrecht System of a balanced BCSR has been
adopted in various countries. In Australia, for example, a commercial laboratory
inVictoriaofersacomprehensivesoiltestingservicebasedontheMikhailSystem
of soil balance, which has similarities to the Albrecht System. Such has been the
interest in the Albrecht System that two scientists at the University of Queensland
undertook an extensive review of the concept of an “ideal” or “balanced” BCSR
(KopittkeandMenzies,2007).heyconcludedthatwithintherangeofvalues
commonlyfoundinsoils,theproportionsofCa,Mg,andKionsandtheirspeciic
ratios do not influence the chemical, physical, or biological fertility of a soil.
Notwithstanding this conclusion, it is recognized, particularly in Australia, that
a soil's exchangeable Na percentage is critical in determining a soil's structural
stability (see box 2.4, chapter 2).
MainstreamsoilsciencedoesnotaccepttheconceptsofanidealBCSRand
ideal cation ratios but focuses on assessing whether the concentrations of available
nutrients are sufficient but not excessive. This approach is called the sufficiency
level of available nutrients, which incorporates the concept of a critical value for an
essential nutrient as determined through soil or plant analysis (see figure 3.8). This
approach is potentially more conservative of fertilizer and soil amendment use than
the BCSR approach and should therefore make better use of scarce resources.
Critical Values and Soil Sampling
The standard approach to interpreting a soil test value involves determining the
rangeoftestvaluesthatcorrespondtoaverydeicient,deicient,adequate,and
excessive nutrient supply—the sufficiency level of available nutrients (see box 3.7).
Although this information should ideally be derived from research trials in vine-
yards, much of these data have been sourced from the more abundant agronomic
trials. A critical value is derived from a response curve, analogous to that shown
in figure 3.8, except that soil test values are plotted on the horizontal axis. This
approach is necessary to ensure soil test values are correctly interpreted, preferably
by a specialist adviser. Also, the normal sampling depth of 0 to 10 cm or 0 to 15 cm
may be inadequate for deep-rooted vines. InWestern Australian vineyards, for
example, it is recommended that soil samples be collected in 10-cm intervals down
to 50 cm. This procedure is labor-intensive if done by augering (see figure 1.13A);
a suitable alternative could be a hydraulic corer (see figure 1.13B). When sampling
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