Consumer awareness of the environment and sustainability has increased in recent years. Market research shows that consumers are increasingly willing to pay premium prices for environmentally friendly products (Behe et al., 2010; Lopez et al., 2009, 2011). Commercial greenhouse operations that produce organic or sustainable crops have a new niche or specialty crop market.
As more greenhouse producers consider implementing organic production practices, questions arise about the use of organic media, fertilizers, and pest management methods for greenhouse crops. Organic media are available in the market, and pest management practices using organic pesticides and biological control agents are being established. However, cultural information about using organic fertilizers in a commercial greenhouse operation lags behind that available for other management areas. Specifically, information about the different organic fertilizers available in the market and their effects on plant growth and quality and substrate pH and electrical conductivity (EC) in comparison with inorganic fertilizers is needed.
Many organic fertilizers are byproducts of livestock, fish, food, and other processing industries (Gaskell and Smith, 2007). Some common materials used as organic fertilizer sources include fishmeal or fish powder, processed fish residues, feather meal, blood meal, meat and bone meal, and manure-based materials (Gaskell et al., 2006; Hartz and Johnstone, 2006).
Fish fertilizers are made from waste products of the ocean-fish processing industry. Fish fertilizers supply mostly NH4-N (Cox, 2010), which could be a disadvantage for some plants. Also, fish fertilizers can be a problem to store because they spoil and can be difficult to inject through some systems (Cox, 2010). Neptune’s fish hydrolysate 2-4-1 is the most commonly available fish fertilizer (Cox, 2010), and it is approved by the Organic Materials Review Institute (OMRI) for organic greenhouses (OMRI, 2012).
Some organic fertilizers are derived from residues (meals) of oilseeds such as soybean or from extracts during processing of oil from the seeds (Nelson et al., 2012). Among these fertilizers, some are OMRI-approved for organic use. Some soybean-based commercial preparations supply nutrients derived from inorganic salts and therefore are not OMRI-approved for organic use.
Other organic fertilizers are derived from alfalfa plants, in which the plant material (leaves) is dehydrated and pelletized (Fasina et al., 1997).
Although organic fertilizers are available in the market, little information is available on their performance, their influence on plant growth and quality, or their N leaching characteristics. Therefore, the objective of this work was to evaluate liquid fish, oilseed extract, and alfalfa pellets, used either alone or in combination, for plant growth and N leaching from two commonly grown floricultural crops, marigold (Tagetes erecta L. ‘First Lady’) and calibrachoa (Calibrachoa ×hybrida Llave & Lex ‘Million Bells Cherry Red’). Calibrachoa was particularly useful in this study because of its high fertility and acidic pH requirements and its tendency to demonstrate nutritional problems (Dole et al., 2002).
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