The increase in consumer demand for organically-grown crops has been recognized by many greenhouse producers in the United
States (e.g. Treadwell et al., 2007).As interestin organic greenhouse
productionincreases inthe U.S.,nutrientmanagementis oftencited
as a key challenge to the adoption of organic production practices
(Burnett and Stack, 2009). Organic substrates typically use a blend
of various allowed bulk materials to achieve appropriate physical
properties (water and air holding capacity). Organic nutrient
management for container production often includes the use of a combination of fertilizers, such as pre-plant amendments with
compost or other organic-certified materials to provide an initial
nutrient charge that is supplemented with liquid organic fertilizers
as the production cycle progresses. Length of the production
cycle often dictates the best strategy for using organic nutrient
sources: shorter production cycles, such as for vegetable transplants,
can often be accomplished solely with nutrients amended
to the substrate pre-plant, but longer-term greenhouse crops, such
as tomatoes, typically require that liquid organic nutrients be
used to supplement pre-plant incorporated nutrients. Ornamental
crops are also produced using organic-based nutrient sources, but
they are frequently produced solely with liquid organic fertilizers
regardless of length of the production cycle.