Organic agriculture is one of the fastest growing segments of U.S. agriculture. In 2011, certified organic growers sold more than $3.5 billion in organically grown agricultural commodities. Between 1992 and 2008 there has been a 361% increase in certified organic operations (Chapin, 2012). In 2010, the U.S. Department of Agriculture (USDA) reported a 7.7% increase in sales of organic products over those in 2009 (USDA, 2012), and this demand continues to grow (Beyond Pesticides, 2012). In response, there has been an increase in the number of organic growers needed to meet this demand.
In organic production, the use of inorganic fertilizer is largely prohibited. As a result, organic growers depend on the use of natural sources such as manures, legume cover crops, animal byproducts, and naturally formed minerals. The pre-plant application of nutrients is an effective practice with a few exceptions, N and potassium (K) being most notable. These two nutrients are required in relatively large quantities and often become limited as a plant grows and matures. As a result, it is recommended to apply a portion of the N and K pre-plant and the remainder be applied throughout the growing season (Kemble, 2012).
The management of in-season fertility can be a limiting factor in the production of high N-demanding crops (Hartz et al., 2010). This is particularly true when polyethylene mulch is used as the surface covering, restricting the ability to surface-apply supplemental fertilizer midseason. This issue is typically overcome by installing drip irrigation beneath the polyethylene mulch to provide water and nutrients. Previously, organic growers have relied on the use of sodium nitrate for this application. Sodium nitrate, however, is being considered for removal from the National Organic Program’s list of allowable synthetic substance and its use banned in organic production (McEvoy, 2012). With the potential loss of sodium nitrate, an injectable organic N source that is allowable in organic production and proven effective is needed to fill this void. HFF has been used as a supplemental fertilizer in organic production for many years (Gaskell and Smith, 2007). Hydrolyzed fish fertilizer is produced through an enzymatic process where fish proteins are broken down into their base amino acids (S.F. Organics, 2013). Unfortunately, there has been limited research as to the effectiveness of such products; thus, research in this area is needed.
The cost per unit of available N has also been a concern as to the profitability of using HFF in organic production (Hartz and Johnstone, 2006). The issue of availability is directly related to N mineralization. Results of previous studies indicated that HFF had one of the fastest and most complete mineralization rates among all liquid organic fertilizers tested. After 2 weeks of incorporation and incubation at 10 to 25 °C, between 47% and 60% of the organic N had been mineralized (Hartz and Johnstone, 2006). Rapid mineralization rates not only supply the plant with quickly available N, but also ensure that the grower receives the full financial and nutritive value of the products applied. Although organically grown products typically command a significant price premium of 60% or more over conventional products, production costs for organic growers are often a limiting factor (Lin et al., 2008). As a result, growers continually search for methods that will maximize profit while reducing overall cost.
The practice of double-cropping is common among vegetable growers who use polyethylene mulch (Rice et al., 2007). This practice reduces production cost by splitting the mulch costs over multiple crops. Growers who will double-crop typically select a crop that is planted immediately after the termination of the previous crop. Often, these are unrelated crops that will thrive under different seasons and that share few pests. This management system not only reduces overhead costs for growers, but it also keeps the land continuously producing a cash crop.
Thus, the objective of the research was to evaluate the use of HFF as a source of organic N along with inorganic N sources at various rates in a plasticulture rotation of yellow squash (Cucurbita pepo cv. Conqueror III) (Seminis Seed Co., St. Louis, MO) and collards (Brassica oleracea var. acephala cv. Blue Max) (Abbott and Cobb, Feasterville, PA).
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