1. The Exchangeable Sodium Percentage (ESP) is a key indicator to monitor sodium problems in soils. The ESP is simply the fraction of the soil CEC occupied by sodium, and ESP>15% is part of the definition for both sodic and saline-sodic soils. Measurement of cation exchange capacity requires several experimental steps and calculations. One method is to add a concentrated solution of ammonium acetate to a soil sample in the lab and collect all the cations that are knocked off from CEC sites by the NH₄⁺. Suppose the end result of this measurement process for a given soil is that the cations exchanged by NH₄⁺ were 5.4 cmol Ca²⁺/kg soil, 1.4 cmol Mg²⁺/kg soil, 2.6 cmol K⁺/kg soil, and 1.9 cmol Na⁺/kg soil. If so, then what is the Exchangeable Sodium Percentage of this soil (in %)?

2. Suppose you read about a 10-year experiment that showed conservation tillage plus cover cropping were able to increase soil organic matter (SOM) by 1.17 Mg SOM/ha in the top 30 cm of soil in their field. You want to convert this result to terms that are easier to understand, such as %SOM in the soil. You look at their soil characterization data and the average bulk density in the top 30 cm of soil was 1.15 g soil/cm³ soil. Given this, what was the SOM gain during the experiment in terms of %SOM by weight?

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