Evaluation of Coconut Coir Dust/Modified Urea–Formaldehyde Resins as a Growing Medium for Pepper Seedlings

in HortTechnology

To produce a firm and cohesive root plug to promote automated transplanting of nursery-grown seedlings, hydrolyzed soy protein-modified urea–formaldehyde (H-UF) resins were used to bind renewable substrate [mixture of coconut (Cocos nucifera) coir dust, coconut fiber, organic manure, perlite, vermiculite]. The resulting substrate block showed high density and nutrient concentrations in the peripheral portion and relatively low density and nutrient levels in the center. The porosity of the H-UF/substrate block was slightly lower than that of standard substrate. The electrical conductivity and pH were beneficial for germination and early seedling development. The modified resins in the substrate block existed in the form of spheres that adhered to each other and formed a porous structure from nano- to micrometer scale. In particular, the H-UF/substrate block increased the seedling height, stem diameter, root length, and leaf area of ‘Sujiao No. 5’ pepper (Capsicum annum) seedlings by 56.07%, 43.33%, 1.33%, and 89.63%, respectively, compared with those of seedlings grown in substrate without H-UF resin. The contents of nitrogen, phosphorus, and potassium in the shoot and root of pepper seedlings grown in H-UF/substrate blocks were enhanced by 39% to 69% compared with those of seedlings grown in standard substrate. The compressive strength of the H-UF/substrate block was 3.6-fold higher than that of substrate when 50% resin was added to the substrate. The results indicated that a combination of the substrate with the modified resin was suitable as a growth substrate for nursery production of pepper seedling plugs.

Abstract

To produce a firm and cohesive root plug to promote automated transplanting of nursery-grown seedlings, hydrolyzed soy protein-modified urea–formaldehyde (H-UF) resins were used to bind renewable substrate [mixture of coconut (Cocos nucifera) coir dust, coconut fiber, organic manure, perlite, vermiculite]. The resulting substrate block showed high density and nutrient concentrations in the peripheral portion and relatively low density and nutrient levels in the center. The porosity of the H-UF/substrate block was slightly lower than that of standard substrate. The electrical conductivity and pH were beneficial for germination and early seedling development. The modified resins in the substrate block existed in the form of spheres that adhered to each other and formed a porous structure from nano- to micrometer scale. In particular, the H-UF/substrate block increased the seedling height, stem diameter, root length, and leaf area of ‘Sujiao No. 5’ pepper (Capsicum annum) seedlings by 56.07%, 43.33%, 1.33%, and 89.63%, respectively, compared with those of seedlings grown in substrate without H-UF resin. The contents of nitrogen, phosphorus, and potassium in the shoot and root of pepper seedlings grown in H-UF/substrate blocks were enhanced by 39% to 69% compared with those of seedlings grown in standard substrate. The compressive strength of the H-UF/substrate block was 3.6-fold higher than that of substrate when 50% resin was added to the substrate. The results indicated that a combination of the substrate with the modified resin was suitable as a growth substrate for nursery production of pepper seedling plugs.

As the use of seedlings in crop production increases in popularity, transplantation is becoming increasingly important in greenhouses (Jiang et al., 2017). Manual planting of seedlings in the field requires numerous workers and considerable effort with fewer people willing to engage in agricultural production in China. Therefore, development of automatic transplanters is important to overcome the labor shortage. However, use of automatic transplanters in vegetable nurseries is hindered because of insufficient root development and root plug cohesion (Boudreault et al., 2014).

Good root development contributes substantially to the optimal quality of plug seedlings. In the process of handling and planting seedlings with a firm root plug are important for the later growth of seedlings. The structural integrity of the root plug is mainly determined by the root system of the vegetable crop. Some vegetables produce relatively underdeveloped root systems. The root system of pepper (Capsicum annum) grows slowly, but the shoot system grows quickly, leading to taller shoots and undeveloped root systems (Leskovar and Stoffella, 1995). Additional studies have shown that combinations of peat, vermiculite, coconut (Cocos nucifera) coir, perlite, and compost in the growth medium can act synergistically to promote seedling root development (Balestri et al., 2015; Gonzálezfernández et al., 2015; Mininni et al., 2015; Ravindran et al., 2016). Urea formaldehyde resin is a low-cost polymeric condensation product of the urea and formaldehyde that is most widely used in slow-release fertilizer, adhesives, finishes, and molded objects because of its fast curing, high reactivity, good bonding performance, lower price, high tensile strength (Qu et al., 2020). The objective of this study was to test soy protein isolates modified urea–formaldehyde resins as a substrate binder on pepper seedling growth. A renewable substrate (coconut coir dust, coconut fiber, organic manures, vermiculite, and perlite) was bonded by soy protein isolate-modified urea–formaldehyde resins to form a substrate block. The effect of the modified resin on the properties of the substrate block was characterized and the growth parameters of pepper seedlings were recorded.

Materials and methods

Materials.

Seedling substrate components (coconut coir dust, coconut fiber, perlite, vermiculite) were purchased from Meizhijia Horticulture Development Co. (Shanghai, China). Urea (≥99.0%) was purchased from Jiuyi Chemical Reagent Co. (Shanghai, China). Formaldehyde (37.0% to 40.0%) and phosphoric acid (≥85.0%) were purchased from Shantou Xilong Chemical Factory (Guangdong, China). Soy protein (protein ≥90%, fat ≤1%, moisture ≤7.0%, ash ≤6.0%, coarse fiber ≤1%) was purchased from Gaomao Biological Technology Co. (Zhejiang, China). Organic manure (composted manure–straw mixture) was purchased from Nanjing Ningliang Bio-engineering Co. (Nanjing, China).

Preparation of hydrolyzed soy protein-modified urea formaldehyde adhesives.

Soy protein was hydrolyzed in potassium hydroxide (KOH) aqueous solutions of 0.056%, 0.23%, 0.39%, and 0.56% by weight at 100 °C for 1 h and designated as A, B, C, and D, respectively. The solid content was 13%. To determine the additive amount of hydrolyzed soy protein (HSP) in the reaction system, the react ability of HSP with formaldehyde was determined by a modified sodium sulfite method (Park and Causin, 2013). Formaldehyde, HSP, and the first urea were added to a 20-L reactor and the solution was heated until the temperature reached 30 °C. The pH of the mixture was adjusted to 7.5 using 25% potassium hydroxide aqueous solutions. The mixture was heated to 90 °C at a rate of 1 °C·min−1 and held at 90 °C for 30 min. Then, the pH of the prepared mixture was adjusted to 4.5 × 25% phosphoric acid solution and maintained until the end of the reaction. After the reaction reached the endpoint, the pH of the mixture was adjusted to 7.5 × 25% potassium hydroxide aqueous solutions. The remaining urea was added after the temperature decreased to 75 °C. The formulations of HSP-modified UF are listed in Table 1. Urea was added separately, which can increase the amount of polymethylol urea, increase the degree of cross-linking of urea-formaldehyde resin, and improve the bonding strength.

Table 1.

Formulation of hydrolyzed soy protein (HSP)-modified urea–formaldehyde resins (H-UF) for binding a growing substrate for growing pepper seedlings.

Table 1.

Preparation of substrate block and obtaining seedlings.

Substrate comprised a mixture of coconut coir dust, perlite, organic manures, vermiculite, and coconut fiber in volume proportions of 6:1:1:1:0.2. First, the substrate was blended with hydrolyzed soy protein-modified urea–formaldehyde (H-UF) in a weight proportion of 8:3. Then, 72-cell plug trays were filled with blended substrate (three trays for each resin). There was a hole in the central part of the substrate block where the substrate could be filled. All the plug trays were dried and cured in an oven at 60 °C for 6 h to form the substrate block. The drying process was the curing process for H-UF resin because condensation water from urea formaldehyde molecules evaporated in the drying process.

‘Sujiao No. 5’ pepper seeds were purchased from Jiangshu Seed Co. (Nanjing, China). The entire tray was manually sown with pepper seeds (72 seedlings). Nursery trays were watered using tidal irrigation every day. During the nursery period, the substrate block provided enough nutrients for the seedlings. The experiment was performed in a greenhouse [15 to 40 °C air temperature, 20% to 90% relative humidity, 400–1200 ppm carbon dioxide (CO2) concentration, 0–55,000 l× illumination intensity]. Data were collected by an intelligent environmental monitoring system developed by researchers from the Institute of Agricultural Facilities and Equipment, Jiangsu Academy of Agricultural Science in Nanjing, China (Liu et al., 2016).

Porosity analysis.

The aeration porosity, water-holding porosity, and total porosity of the substrate and the substrate block were determined in situ technique (Rosen, 2000; Spomer, 1977): aeration porosity (percent) = [(W1W2)/V] × 100; water-holding porosity (percent) = [(W2W3)/V] × 100; total porosity (percent) = aeration porosity + water-holding porosity; where W1 is the weight of the substrate after being immersed in water for 24 h, W2 is the weight of the substrate after the water was drained, and W3 is the weight of the dried substrate.

Chemical analysis.

Electrical conductivity (EC) and pH of the substrate and substrate block were analyzed using a 1:5 (v/v) water-soluble extract. Nutrient contents of the substrate and seedling were tested. The total nitrogen (N) content was determined using the Kjeldahl method (Kjeldahl, 1883). The phosphorus (P) content was measured colorimetrically, as described by Kitson and Mellon (1944). Potassium (K) content was measured by flame photometry (FP6450 flame photometer; Shanghai Xinyi Instrument Co., Shanghai, China). The available N was determined by the sodium hydroxide hydrolysis diffusion method. Available P and K were extracted by sodium bicarbonate and ammonium acetate, respectively.

Growth parameters.

At the end of the nursery seedling growth period (60 d), the growth parameters were recorded. The roots were cleaned with distilled water and dried with paper towels. Root fresh weight and dry matter of the aboveground and underground parts were measured by an analytical balance (FA2004; Shanghai Shangtian Precision Instrument Co., Shanghai, China). Seedling height of the aboveground part, root length, and stem diameter (height, 2 cm) were measured using a vernier caliper. The leaf area of each plant was measured using a leaf area meter (YMJ-A; Ningbo Kemai Instrument Co., Ningbo, China). SPAD values of the third leaf from the top were measured (CCM-200 plus; Opti-Sciences, Hudson, NH) and 10 readings were performed for each sample. Pigments were extracted from leaf discs with methanol in the dark at 4 °C for 48 h. Spectrophotometric measurements (Lambda 35 ultraviolet spectrophotometer; PerkinElmer, Waltham, MA) were taken at 665 and 649 nm to determine chlorophyll a and b concentrations according to Lichtenthaler (1987). Three pepper seedlings per treatment were randomly collected for the growth parameter. The seedlings were also transplanted to the field after the nursery seedling growth period.

Mechanical properties and morphology.

A tensile testing machine (HY-0580; Shanghai Hengyi Precision Instrument, Shanghai, China) was used to measure the compressive properties of the substrate block. The strength was determined at a crosshead speed of 10 mm·min−1. Three replicates were tested for the substrate block to obtain an average value.

Peak force tapping was used to investigate the morphology of UF resins (Dimension Icon; Bruker AXS, Karlsruhe, Germany). Images of the C-UF resin were analyzed using NanoScope software (Bruker Corp., Santa Barbara, CA).

Statistical method.

Substrate blocks bonded with four different kinds of resin were applied during the experiment and the data were analyzed by a one-way analysis of variance with the UF resin type as one factor using SPSS statistical software (SPSS version 17.0; IBM, Armonk, NY). The least significant difference was calculated to compare the differences between means in each treatment.

Results and discussion

Description of the substrate block.

Seedlings are sensitive to negative factors, such as pH, salinity, and phytotoxicity, in the growing medium during the germination and initial growth stages (Carmona et al., 2012). Therefore, seedling substrates must be of higher quality than the culture substrates used for postseedling stages. Hence, a customized nutrient-containing substrate block was prepared. The substrate block possessed relatively high density and nutrient content due to the added resin (Fig. 1). Substrate with low density and nutrient content were filled in the central section of the block. The lower nutrient and EC values of the substrate promoted seed imbibition, which was beneficial for pepper seeds germination (El-Mahrouk et al., 2017; Finchsavage and Footitt 2017). It has been reported that excess soluble salts and ammonium ions (NH4+) will delay or reduce germination and delay the initial seedling development of pepper (Rekik et al., 2017; Roe et al., 1997). The surrounding bonded substrate provided sufficient nutrients for seedling growth at advanced developmental stages.

Fig. 1.
Fig. 1.

Schematic illustration (A) and photograph (B) of a substrate (mixture of coconut coir dust, coconut fiber, organic manure, vermiculite, and perlite) block bonded with modified urea–formaldehyde resins as a growing medium for pepper seedlings.

Citation: HortTechnology hortte 30, 3; 10.21273/HORTTECH04542-19

Properties of different substrate block.

Adequate aeration properties are of critical importance for root growth and uptake of water and nutrients (Boudreault et al., 2014; Gargiulo et al., 2016; Liu et al., 2017). The aeration and water-holding porosity of the substrate block were decreased due to the modified resins (Table 2). The ratio of aeration porosity to water-holding porosity of different substrate blocks was nearly the same. The percentage of the modified resins that occupied the aeration and water-holding porosity was largely consistent. The different types of resins had little influence on the porosity of the substrate block.

Table 2.

Physical and chemical properties of substrate blocks bonded with modified urea–formaldehyde (UF) resins used for growing pepper seedlings. Data are the means of three replicates.

Table 2.

The hydrophilic groups, such as the hydroxyl groups, carboxyl groups, and amino groups, in the substrate can react with modified resins for condensation (Byung-Dae et al., 2010; Singh et al., 2014). Therefore, water absorption was less than the substrate, and a sufficient amount of oxygen (O2) was provided by the well-drained and well-aerated substrate block for root respiration. Root growth can be improved by preventing O2 deficiency and excess CO2 (Ok et al., 2015). This enables the production of high-quality seedlings with an extensive root system. The substrate block developed in the present study was suitable for pepper, which was sensitive to an overabundance of moisture and waterlogging (Mardaninejad et al., 2017).

Most solanaceous vegetable crops (Solanaceae) grow better in weakly acid substrates (pH 5.2–7.0). The cured modified resins resulted in a slightly acidic pH in the substrate blocks (6.37–6.63), which was also favorable for the growth of pepper seedlings (Cao et al., 2017).

The stability of the substrate was another important criterion (Ok et al., 2015). During nursery seedling production, perlite rises to the surface of the substrate because of its low density in substrate. The other components in the substrate become increasingly compacted under the action of gravity. When modified resins are incorporated in the substrate, the substrate components are fixed in position and the total void space volume will not decrease during seedling production. Therefore, the properties of the substrate block are more beneficial for the growth of pepper seedlings.

Seedling growth experiments.

The pepper seedlings grown in substrate with modified UF resins showed remarkable increases in growth parameters compared with those for the standard substrate (Table 3). The increases were significant for all parameters except root length. In particular, the C-UF resins resulted in the greatest promotion of seedling growth. Fresh shoot weight and root weight were increased by 1.83- and 2.04-fold, respectively, compared with those of plants grown in substrate alone. Similarly, shoot dry weight and root dry weight increased by 2.82- and 2.11-fold compared with those of plants grown in substrate alone. When substrate was bonded by C-UF resin, seedling height, stem diameter, root length, and leaf area increased compared with those of seedlings grown in substrate alone. Increases in biomass production with the use of modified resins as a substrate component may be attributed to the sufficient porosity and the slow release of nutrients provided by the H-UF (Cendreromateo et al., 2015; Ok et al., 2015). This enables production of high-quality seedlings with an extensive root system. The substrate block developed in the present study was suitable for pepper (Mardaninejad et al., 2017).

Table 3.

Growth parameters of pepper seedlings grown in substrate alone and substrate block bonded with modified urea–formaldehyde (UF) resins. Data are means of three replicates.

Table 3.

It is well known that leaf N status (chlorophyll a and b contents) is an important indicator of the photosynthetic activity and nutritional status of seedlings (Eitel et al., 2011). The SPAD values showed that the chlorophyll content of pepper leaves grown in substrate blocks were significantly higher (19% to 79%) than those of seedlings grown in substrate alone. Leaves of pepper seedlings grown in substrate bonded by C-UF were significantly higher in chlorophyll a content and chlorophyll b content compared with those of seedlings grown in substrate alone. These results showed that the modified resins resulted in increased leaf chlorophyll content, which was consistent with the results of biomass production.

Pepper seedlings grew well in the substrate blocks from germination through the growth phase and to the blossom period (Fig. 2). The roots readily penetrated the substrate blocks. The bonding of the components of the substrate blocks was maintained in a humid environment for 40 d. After transplanting, the roots of the substrate block grew outward and extended in all directions. Moreover, the substrate block provided nutrients for the plant after transplanting.

Fig. 2.
Fig. 2.

Pepper seedlings grown in substrate/C-UF resin [hydrolyzed urea formaldehyde resin modified by soy protein hydrolyzed in 0.39% (by weight) potassium hydroxide aqueous solution] blocks: (A) seedling with two leaves, (B) 40-d seedlings, and (C) roots of pepper seedling 10 d after transplanting.

Citation: HortTechnology hortte 30, 3; 10.21273/HORTTECH04542-19

Nutrient composition.

The N and the available N content increased with an increase in hydrolysis of the HSP (Table 4). More HSP was added to modify the UF with a lower degree of hydrolysis. The N content in the HSP was lower than that in urea formaldehyde resins. The P and K in substrate blocks were nearly the same. Incorporation of C-UF with the substrate resulted in greater contents of total N, P, and K compared with those of substrate alone.

Table 4.

Nutrient content of the substrate and substrate blocks as a growing medium for pepper seedlings. Data are means of three replicates.

Table 4.

The contents of N, P, and K in the shoots of seedlings grown in substrate/C-UF were enhanced compared with those of seedlings grown in substrate alone (Table 5). Increases of 62.80%, 68.91%, and 40.03% in the N, P, and K contents, respectively, of the roots grown in substrate/C-UF were observed compared with those grown in substrate alone. However, when the N exceeded 89.022 mg·g−1 in the substrate block, the N content in pepper did not increase. The nutritional (N, P, and K) composition of the pepper shoot and root indicated that greater quantities of the nutrients were used by the seedlings grown in the substrate block. The results support that modified UF resins can enhance nutrient availability for the pepper seedlings.

Table 5.

Nitrogen, phosphorus, and potassium contents in the shoots and roots of pepper seedlings grown in substrate alone and substrate bonded with a modified urea–formaldehyde (UF) resin. Data are means of three replicates.

Table 5.

Mechanical properties of the substrate block.

The mechanical hand is crucial technology for mechanized transplanting of plug seedlings and makes direct contact with the root plug. Therefore, the compressive properties of the substrate block are of vital importance. The compressive strength of the substrate block increased with the percentage of resin content (Fig. 3). In comparison with the substrate alone, the compressive strength of the substrate/C-UF was higher than that of the standard substrate when 50% (by weight) resin was added to the substrate. The compressive strength of the substrate block was enhanced with the increasing degree of hydrolysis of HSP. After 40 d of seedling growth, the modified resins with a lower degree of HSP hydrolysis had degraded more rapidly than those with a higher degree of HSP hydrolysis (Qu et al., 2015). The cross-linked structure of A-UF resins was decomposed more extensively, leading to a more rapid decrease in compressive strength. The HSP with a lower degree of hydrolysis rendered the cross-linking structure of the modified resins sparser due to the large molecular weight and large size of the HSP (Qu et al., 2015). The low cross-linking degree increased the polymer chain segment flexibility, which increased the susceptibility of such resins to microorganisms (Arancibia et al., 2014; Okada 2002).

Fig. 3.
Fig. 3.

Compressive strength of substrate blocks bonded with modified resins differing in degrees of protein hydrolysis and in percentages of modified resin content (uncertainty is represented by the error bar) [A-UF, B-UF, C-UF, and D-UF: urea formaldehyde resins (UF) modified by soy protein hydrolyzed in 0.056%, 0.23%, 0.39%, and 0.56% (by weight) potassium hydroxide aqueous solutions]. 1 MPa = 145.0377 psi.

Citation: HortTechnology hortte 30, 3; 10.21273/HORTTECH04542-19

Microstructure of the substrate block.

The surface microtopography of the C-UF/substrate block showed pores in the range of 1 to 10 μm (Fig. 4). Modified resins are present in the form of spheres that adhere to each other. The indices of porosity and microtopography are good indicators of the porosity of the growing medium, which determines the rate at which air (O2) can diffuse through the substrate (Jayasinghe et al., 2010).

Fig. 4.
Fig. 4.

Scanning electron micrographs of a substrate/C-UF resin [urea formaldehyde resin modified by soy protein hydrolyzed in 0.39% (by weight) potassium hydroxide aqueous solution] block as a medium for growing pepper seedlings (left = ×300, right = ×1000). 1 μm = 1 micron.

Citation: HortTechnology hortte 30, 3; 10.21273/HORTTECH04542-19

The morphology of C-UF resin particles in the substrate block before and after seedling growth was characterized by an atomic force microscope (Fig. 5). Resin particles formed a spherical structure after the cross-linking reaction (Park and Causin, 2013). These results are in accordance with the scanning electronic microscopy observations using microtopography. The spherical particle size of the resins in the substrate block was ≈100 nm, which bonded together and formed a porous structure ranging from 100 to 300 nm. This may have occurred because the tridimensional network was formed during the curing process. The cured modified resins have a loose and porous structure, which is beneficial for the provision of O2 to the root system. In addition, the porous nano-structure formed by the modified resins contributed to the increased adsorption capacity and surface area of the substrate, thus promoting maintenance of the absorbable nutrient solution around the roots (Ahmad et al., 2014).

Fig. 5.
Fig. 5.

Atomic force microscope images of C-UF resin [urea formaldehyde resin modified by soy protein hydrolyzed in 0.39% (by weight) potassium hydroxide aqueous solution] particles in a substrate block for growing pepper seedlings before and after seedling growth for 40 d. Two-dimensional (A) and three-dimensional (B) height images of C-UF before seedling growth. Two-dimensional (C, E, G) and three-dimensional (D, F, H) height images of C-UF after seedling growth. 1 μm = 1 micron.

Citation: HortTechnology hortte 30, 3; 10.21273/HORTTECH04542-19

After seedling growth for 40 d, the degraded modified resins were extremely rough (Fig. 5G and H). Large pores (diameter, 2 μm) were formed. The spherical particles decreased in size by approximately half. In particular, the growth of beneficial microorganisms was induced on the surface of modified UF resins (Qu et al., 2015), as revealed in atomic force microscope micrographs. Previous research has shown that beneficial microorganisms may enhance the uptake of macronutrients by maize plants in soil (Kim et al., 2017; Rehman et al., 2016). The activity of a suite of enzymes secreted by the microorganisms may improve the nutrient uptake by pepper seedlings.

Conclusions

Growers can use the modified UF resins to bind the substrate; then, they can dry and cure the bound substrate in an oven to obtain the substrate block. The HSP-modified UF resins assisted pepper seedlings in forming a firm and cohesive root plug. In addition, sufficient porosity and the slow release of nutrients were provided by the resin. The nutrient-customized substrate block was beneficial for germination and early seedling development. The substrate block contained fixed void spaces and pore stability. The nanostructured pore, micro-pore structure, and macro-pore structure were suitable for adequate nutrient and O2 supplies to the root system. Pepper seedlings grown in the substrate control and seedlings grown in substrate blocks achieved superior growth and nutrition. The compressive strength of the substrate/C-UF was higher than that of the standard substrate, which was conducive to mechanized transplanting. The roots were able to penetrate the substrate blocks and extend outward in all directions after transplanting. The added cost per seedling is ≈$0.002. Therefore, the standard substrate bonded by C-UF resins is an ideal growing medium for pepper seedlings.

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  • RehmanM.Z.U.RizwanM.AliS.FatimaN.YousafB.NaeemA.SabirM.AhmadH.R.OkY.S.2016Contrasting effects of biochar, compost and farm manure on alleviation of nickel toxicity in maize (Zea mays L.) in relation to plant growth, photosynthesis and metal uptakeEcotoxicol. Environ. Saf.133218225

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  • RekikI.ChaabaneZ.MissaouiA.BouketA.C.LuptakovaL.ElleuchA.BelbahriL.2017Effects of untreated and treated wastewater at the morphological, physiological and biochemical levels on seed germination and development of sorghum (Sorghum bicolor (L.) Moench), alfalfa (Medicago sativa l.) and fescue (Festuca arundinacea Schreb.)J. Hazard. Mater.326165176

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  • RoeN.E.StoffellaP.J.GraeetzD.1997Composts from various municipal solid waste feedstock affect vegetable crops. I. Emergence and seedling growthJ. Amer. Soc. Hort. Sci.122427432

    • Search Google Scholar
    • Export Citation
  • RosenC.J.2000Compost criteriaAmer. Nurseryman1911322330

  • SinghA.P.CausinV.NuryawanA.ParkB.D.2014Morphological, chemical and crystalline features of urea-formaldehyde resin cured in contact with woodEur. Polym. J.56185193

    • Search Google Scholar
    • Export Citation
  • SpomerL.A.1977How much total water retention and aeration porosity in my container mix?Illinois State Florists Assn. Bul.3691315

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Contributor Notes

This work was financially supported by a regional collaborative innovation project (science and technology assistance Xinjiang project) (grant no. 2018E02035); the National Natural Science Foundation of China (grant no. 11605077); China scholarship council (grant no. 201808320076); and Jiangsu Province Agricultural Independent Innovation Fund (grant no. CX(19)2003).H.Y. and P.Q. are the corresponding authors. E-mail: haijunyancau@163.com or qupinghappy@163.com.
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    Schematic illustration (A) and photograph (B) of a substrate (mixture of coconut coir dust, coconut fiber, organic manure, vermiculite, and perlite) block bonded with modified urea–formaldehyde resins as a growing medium for pepper seedlings.

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    Pepper seedlings grown in substrate/C-UF resin [hydrolyzed urea formaldehyde resin modified by soy protein hydrolyzed in 0.39% (by weight) potassium hydroxide aqueous solution] blocks: (A) seedling with two leaves, (B) 40-d seedlings, and (C) roots of pepper seedling 10 d after transplanting.

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    Compressive strength of substrate blocks bonded with modified resins differing in degrees of protein hydrolysis and in percentages of modified resin content (uncertainty is represented by the error bar) [A-UF, B-UF, C-UF, and D-UF: urea formaldehyde resins (UF) modified by soy protein hydrolyzed in 0.056%, 0.23%, 0.39%, and 0.56% (by weight) potassium hydroxide aqueous solutions]. 1 MPa = 145.0377 psi.

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    Scanning electron micrographs of a substrate/C-UF resin [urea formaldehyde resin modified by soy protein hydrolyzed in 0.39% (by weight) potassium hydroxide aqueous solution] block as a medium for growing pepper seedlings (left = ×300, right = ×1000). 1 μm = 1 micron.

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    Atomic force microscope images of C-UF resin [urea formaldehyde resin modified by soy protein hydrolyzed in 0.39% (by weight) potassium hydroxide aqueous solution] particles in a substrate block for growing pepper seedlings before and after seedling growth for 40 d. Two-dimensional (A) and three-dimensional (B) height images of C-UF before seedling growth. Two-dimensional (C, E, G) and three-dimensional (D, F, H) height images of C-UF after seedling growth. 1 μm = 1 micron.

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    • Search Google Scholar
    • Export Citation
  • RekikI.ChaabaneZ.MissaouiA.BouketA.C.LuptakovaL.ElleuchA.BelbahriL.2017Effects of untreated and treated wastewater at the morphological, physiological and biochemical levels on seed germination and development of sorghum (Sorghum bicolor (L.) Moench), alfalfa (Medicago sativa l.) and fescue (Festuca arundinacea Schreb.)J. Hazard. Mater.326165176

    • Search Google Scholar
    • Export Citation
  • RoeN.E.StoffellaP.J.GraeetzD.1997Composts from various municipal solid waste feedstock affect vegetable crops. I. Emergence and seedling growthJ. Amer. Soc. Hort. Sci.122427432

    • Search Google Scholar
    • Export Citation
  • RosenC.J.2000Compost criteriaAmer. Nurseryman1911322330

  • SinghA.P.CausinV.NuryawanA.ParkB.D.2014Morphological, chemical and crystalline features of urea-formaldehyde resin cured in contact with woodEur. Polym. J.56185193

    • Search Google Scholar
    • Export Citation
  • SpomerL.A.1977How much total water retention and aeration porosity in my container mix?Illinois State Florists Assn. Bul.3691315

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