The Rapitest Soil Test Kit Measures the pH of soil to get a reading on soil acidity. This test measures the three major components of fertilizer: nitrogen, phosphorus, and potash. Each test can be performed 10 times (40 total tests). Plants need correct ph to control how well plants utilize the nutrients that are available for them. This soil test kit makes testing your soil simple, quick, and easy, simply 1) mix soil with water, pour off liquid after the soil settles into the chambers of the color compactor, 2) dissolve tablet, and 3) compare the color for test reading chart that is included in the kit.