Comparison of Four Commercially-Available Soil Testing Kits to Two Professional Labs for Nitrate, Potassium, Phosphorus and pH.

To determine if commercially-available soil-testing kits are effective, we compared the differences in the results gathered between four different kits (Luster Leaf Rapitest, L.L. Professional, Ferry Morse Premium, and Mosser Lee Master) , as well as two university labs (Texas A&M and LSU).  Soil was collected at the Rhoden Farm in Abilene, TX and then analyzed using four kits by students in lab sections of Soil Science at Abilene Christian University.  All results included measures of soil pH, phosphorus, and potassium, and all but one included nitrate levels.  We found that the kits were significantly lower for P (P < 0.001), K (P < 0.001), and pH (P < 0.001) than the results from the labs.  Nitrate was statistically similar to the results from Texas A&M for three of the kits, with only one kit significantly higher (P = 0.002).  The results from the two professional labs differed significantly for P (P < 0.001), K (P = 0.013), calcium (P < 0.001), magnesium (P < 0.001), and sulfur (P < 0.001).  Importantly, the kits were mostly reliable for measuring nitrate but not for P, K, or pH.  Most surprising was how different the results were from the two professional labs.