T. R. Peck, P. N. Soltanpour, The principles of soil testingWesterman, R L (Ed ) Soil Science Society Of America Book Series, No 3 Soil Testing And Plant Analysis, Third Edition Xxvii+784p Soil Science Society Of America, Inc. pp. 1- 9 ,(1990) , 10.2136/SSSABOOKSER3.3ED.C1