An In-Depth Analysis of Water and Nutrient Management In the Nursery and Greenhouse Industry In Maryland

Agriculture contributes a substantial portion of non-point source nutrient and sediment loads that reach the Chesapeake Bay.  Research in this area has traditionally focused on agronomic farm contributions, with limited research on the nursery and greenhouse industry.  In order to obtain a better understanding of the impact of this industry in Maryland, site specific data was collected.  All known operations in the state (approximately 350 were mailed information about the project, and asked to voluntarily participate.  Of those, 47 operations agreed to site visits and were interviewed to better understand current nutrient, irrigation, and management practices.  Data was gathered at the management unit level (groups of plants managed similarly) for: fertilizer ratio, rate, and timing, irrigation use by season, and nutrient irrigation/runoff mitigation practices.  Of the operations that were visited, 27 had a greenhouse component, with a total of 188 management units and 64 acres of greenhouse production area.  Twenty-seven operations had a container-production area representing 155 management units, totaling 177 acres (not including roadways, buildings and vegetative buffers).   Seventeen field operations were visited, with 96 management units covering approximately 1050 acres of growing area (not including roads and buildings). Rates of N, P₂O₅ and K₂0 applied were found to vary greatly for similar container sizes in both greenhouse and container nursery operations, with minimum and maximum values often varying by an order of magnitude or more.  Field operations were found to have similar nutrient application rates, while irrigation rates were more variable.  Based on this research a number of recommended rates are reported for a variety of container sizes and species.  For example from the container database, there were 22 management units that reported using 8 L containers.  Nitrogen rates varied from 116 kg N/ ha to 709 kg N/ ha for operations in the lower and upper quartile respectively.  It was also found that the amount of water applied per hectare had large variations, even within similar container sizes and spacing.  Summer irrigation rates varied from 91,000 to 356,000 L / ha for lower and upper quartile values respectively.  In general greenhouse and container nursery operations had a wide range of values for fertilizer application rate and irrigation volume for similar plant types and spacings.  We concluded that a majority of growers can likely reduce irrigation and/or fertilization rates without affecting plant quality since similar operations are producing similar plants with lower water and nutrient rates.