COMPARISON OF EXTRACTION METHODS FOR TESTING PH AND ELECTRICAL CONDUCTIVITY OF SUBSTRATES AMENDED WITH DIFFERENT PHOSPHORUS SOURCES USED TO GROW MARIGOLDS^©

Phosphorus (P) is one of the major elements essential for plant growth. Commercial P fertilizers are typically derived from phosphate rock, but the world’s supply of mined phosphate is limited. Biosolids and animal manures are rich in P that can be reclaimed to produce struvite (magnesium ammonium phosphate hexahydrate). Struvite has the potential to replace mined fertilizer P in the soilless substrates used for container plant production. Utilizing struvite from wastewater could enhance nutrient use efficiency and sustainability of container production systems.