Apparently the total content and the available content of a macronutrient are two different measures for the macronutrient in soil, and it is the availability ratio (i.e., available concentration/total concentration) that represents the potential effectiveness of a specific macronutrient in soil.
Availability Ratio. The availability ratio of a soil macronutrient (N, P, or K) at a given location is calculated using the following equation:
where R represents the availability ratio (%); u refers to a specific location; A(u) is the available concentration of a soil macronutrient at location u with a unit of mg/kg; T(u) is the total concentration of the soil macronutrient at location u with a unit of g/kg.
This may explain why the availability ratio of N is less correlated with other soil properties (the largest correlation coefficient is with SOM, which is -0.135, P < 0.01).
After the spatial distribution maps of the total and available contents of a macronutrient were obtained, its availability ratio map could be further derived from the total content map and available content map by using (1) (i.e., at each spatial location, availability ratio = available content/total content).
TN and AN contents have similar spatial patterns, but N availability ratio has a different spatial pattern; however, the spatial patterns of availability ratios of P and K are only similar to those of their available components (i.e., AP and AK), respectively.
Because the availability ratio of a macronutrient is related with its availability (or efficiency) to plants and its risk of loss into deep soil or water body, proper adjustment of macronutrient availability ratios in soil through some measures (e.g., fertilization, liming to change soil pH) may be helpful to improving agricultural productivity and reducing environmental hazards.
In addition to macronutrients, micronutrients and trace metals in soil also have similar problems, and their availability ratios in soil are also important indices for agricultural and environmental management.
Burrluck attributed the 100 per cent sales increase forecast for 2012 to Volkswagens competitively priced 2012 models, Samaco's extensive investment in parts availability which combined with a regional genuine parts supply outlet in Dubai confirms a high parts availability ratio
to enhance customer satisfaction.