Fertility management of seedlings and transplants is considered a key challenge in organic greenhouse production. This study was conducted to determine the response of greenhouse-grown cucumber (Cucumis sativus) and nutrient release profile to two organic fertilizers and their combinations applied at three different concentrations in organic substrate. The organic fertilizers used were a turkey litter–based compost (TC) and a dairy manure vermicompost (VC). In addition, two control treatments [no fertilization (CK), conventional liquid fertilizer (CF)] were included. For TC, substrate leachate pH decreased for the first 17 days after addition and then increased, whereas electrical conductivity (EC), and calcium (Ca) and nitrate-nitrogen (NO3−-N) concentrations increased and then declined. For VC, EC decreased continuously over time from days 0 to 52, whereas pH increased. The Ca and NO3−-N concentrations decreased over time to 24 days and then did not change further. For TC/VC combinations, EC was stable for the first 17 days and then declined. For all organic fertilizer applications, potassium concentration was stable for the first 17 days and then decreased, whereas most of the sodium, ammonium-nitrogen, and chloride were no longer leached by 24 days. The VC and TC/VC combinations did not affect cucumber seed germination rate, seedling survival rate, seedling height, and leaf greenness (SPAD) as compared with CF. The stem length, leaf number, dry weight (DW), root index, and SPAD readings of cucumber transplants increased with increasing TC and VC fertilizer applications. The TC/VC combinations increased the biomass of cucumber transplants compared with CK, and did not differ from CF. The results of this study indicated that the 28.32 lb/yard3 of VC (high rate) or the 9.44 lb/yard3 of VC combined with 4 lb/yard3 of TC (medium rate) can be substituted for CF for the cultivation of cucumber seedlings. Based on DW, the 12 lb/yard3 of TC (high rate) or the 4 lb/yard3 of TC combined with 9.44 lb/yard3 of VC (medium rate) fertilizers were suitable replacements for CF for the cultivation of cucumber transplants.
The increase in consumer demand for fresh organic fruits and vegetables has been recognized by many greenhouse producers throughout the world, including China and the United States (Burnett et al., 2016; Meng et al., 2017; Olczyk et al., 2007; Treadwell et al., 2007). Among organic greenhouse production practices, fertility management of seedlings and transplants is considered a key challenge (Brace, 2017). Unlike inorganic fertilizers, organic nutrients from plant- and animal-based residues are often not immediately available to plants after application. One of their main difficulties is the timing of microbially mediated nutrient release in relationship to plant growth (Bi et al., 2010; Burnett et al., 2016). In addition, the feedstocks and methods for producing organic fertilizers are extremely variable, which results in different components and physiochemical properties among different organic fertilizers. Many traditional organic fertilizers are produced as composts or other formulated byproducts of livestock, fish, and food and other processing industries, including feather meal, blood meal, meat and bone meal, and manure-based materials (Bi et al., 2010; Gaskell and Smith, 2007).
Vermicomposts, produced using the fragmentation of organic wastes by earthworms, have a fine particulate structure and contain nutrients in forms that are more readily taken up by the plants, such as NO3−-N, available phosphorus, potassium (K), Ca, and magnesium (Arancon et al., 2006; Atiyeh et al., 2000; Brace, 2017; Yang et al., 2015). Arancon et al. (2006) reported that food waste and paper waste vermicomposts can increase the amount of ammonium-nitrogen (NH4-N), NO3-N, and orthophosphates in soil on the harvest date. Vermicompost amendment has been shown to increase the growth, yield, or quality of some greenhouse crops, such as tomato (Solanum lycopersicum), pepper (Capsicum annuum), and cucumber (Arancon et al., 2004; Atiyeh et al., 2000; Zhao et al., 2010). Atiyeh et al. (2000) reported that incorporation of 10% or 20% pig solid vermicomposts into a standard commercial horticultural potting substrate (Metro-Mix 360; Sun Gro Horticulture, Agawam, MA) increased the growth of marigold (Calendula officinalis) and tomato seedlings as compared with the standard commercial horticultural potting substrate alone, even when all required mineral nutrients were supplied.
Composting is generally defined as the biological aerobic transformation of an organic byproduct into a different organic product that can be added to the soil without detrimental effects on crop growth (Atiyeh et al., 2000; Baca et al., 1992). The application of composted manure is a common practice in organic culture (Hartz and Johnstone, 2006). Hartz and Johnstone (2006) reported on the effect of temperature on nitrogen (N) availability from feather meal, seabird guano, fish powder, and blood meal in soil. For blood meal after 1 week, 18% of N had mineralized at 10 °C, and 51% had mineralized at 25 °C. By 2 weeks, across materials, approximately half or more of all N had mineralized at 25 °C. Burnett et al. (2016) suggests that substrate-incorporated organic fertilizers are typically used as the sole fertilizer source only for short-term crops because a large proportion of organic nutrients are mineralized within the first few weeks and can leach out of container mixes. Therefore, a difficulty with using organic fertilizers is matching the rate of nutrient release to the plant’s nutrient demands (Burnett et al., 2016; Treadwell et al., 2007).
Cucumber is an important greenhouse vegetable crop and one of the most popular members of the cucurbit (Cucurbitaceae) family (Alsadon et al., 2016). In 2017, world production of cucumbers and gherkins was 84 million tonnes, led by China with 77% of the total (Food and Agriculture Organization of the United Nations, 2019). The objective of this study was to evaluate the effects of organic fertilizer source and rate of application on nutrient leaching over time and to determine the growth response of greenhouse-grown cucumber to two different organic fertilizers.