Sims and A. Wolf, eds., Recommended Soil Testing Procedures for the Northeastern United States. Northeast Regional Bulletin #493. Newark: Agricultural Experiment Station, University of Delaware.</ref>. This SME procedure should also be used to measure concentrations of [[soluble salts]] and [[nitrogen]] in green roof growing media. | Sims and A. Wolf, eds., Recommended Soil Testing Procedures for the Northeastern United States. Northeast Regional Bulletin #493. Newark: Agricultural Experiment Station, University of Delaware.</ref>. This SME procedure should also be used to measure concentrations of [[soluble salts]] and [[nitrogen]] in green roof growing media. |