Relationships variability, natural soils

The relationship between extent of dissociation and pH is important because pH can vary sizeably in natural environments. For example, variability in soil pH is marked, suggesting that the behaviour of ionizable species within soils will be different also. 

Despite the natural occurrence of strong positive relationships that can develop between bacteria and plants, anthropocentric attempts at applying bacteria for biocontrol purposes have had limited commercial success, notwithstanding advances in our understanding of the molecular mechanisms governing biocontrol interactions in the rhizosphere. The inconsistent performance of biocontrol bacteria in the field could be due to variable expression of genes involved in biocontrol, or merely the resistance of established soil communities to a sudden and inundative influx of adventive bacterial species or strains. 

Many parameters in the modeling of soil physies exhibit nonlinear relationships. One sueh relationship is the water retention rate as a function of matric potential, which defines for water flow a term similar to electric potential for eurrent flow. (See J. Nat. Resour. Life Sci. Educ., Vol. 27, 1998, pp. 13-19 for a deseription of the data set for this example.) Figure 9.45 shows experimental data for soil volume water content vs. matric potential. The data points are approximately equally spaced on a log scale of the independent variable. From the data points plotted on a log scale it seems apparent that the data points should all be weighted equally and this is the default used in all the previous data fittings. This will occur naturally for the data fitting even when the points are non-uniformly spaced along the x-axis. 

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