Final answer:
Jack is using small earthen dams as a water conservation method. These dams hold precipitation water, allowing it to infiltrate the soil and eliminate runoff.
Step-by-step explanation:
Jack is using the method of small earthen dams in the furrows between the ridges on which he plants crops as a water conservation method. This method conserves water by holding precipitation water between the dams, allowing the water to infiltrate the soil and eliminate runoff.