What is the immediate action required after collecting soil samples?

The immediate action required after collecting soil samples is to place them in a cooler on ice. This practice is essential to preserve the integrity and accuracy of the samples, as fluctuations in temperature can lead to changes in the chemical and biological properties of the soil, potentially affecting the test results. Keeping the samples cool helps to slow down any microbial activity and chemical reactions that could alter the composition of the soil before testing.

Other options do not provide the same level of preservation needed for soil samples, as storing them at room temperature or in a zip-lock bag could lead to deterioration of the samples. Sending them directly to the lab is important, but without the necessary cooling, the samples might not yield reliable results upon analysis. Thus, using a cooler with ice is the most appropriate and effective method to maintain sample quality until they can be tested.