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Kuan Qin and Daniel I. Leskovar

, combined, can increase watermelon WUE and water conservation ( Yang et al., 2017 ). In addition to these practices, organic input, which includes the application of organic materials (compost, humic substances, biochar, etc.), cover crop residues, and

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Timothy K. Hartz and Thomas G. Bottoms

The use of humic substances (HS) to improve crop growth has been the subject of a substantial body of research over decades. HS refers to a complex, heterogeneous mixture of organic materials arising from the decay of plant and animal residues

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Ruiqin Bai and Deying Li

passed. Table 1. Analysis of variance for turfgrass quality of perennial ryegrass. Data were from 5 weeks after petroleum-based spill (diesel, gasoline, and hydraulic fluid) applied at 15 L·m −2 and remediation (nitrate, humic substance, activated

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Sofía Gómez and Celina Gómez

, no studies have evaluated their potential use for indoor farming applications with sole-source lighting. Humic substances are often derived from the decomposition of organic matter through the metabolic activity of soil microbes ( Bulgari et al

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A.J. Pertuit Jr., Jerry B. Dudley, and Joe E. Toler

New Mexico-mined raw leonardite was characterized by comparing it with the International Humic Substances Society's Standard Leonardite. In the first experiment, adding as little as 1/64 leonardite (v/v) to a sand medium increased tomato [Lycopersicon esculentum (L.) Mill. `Mountain Pride'] root and shoot growth compared with plants produced with fertilizer alone. Growth increased linearly with increasing leonardite levels, from 0% to 25%; however, 50% leonardite inhibited growth. In a second experiment, leonardite alone had no effect on plant height, shoot or root fresh and dry weight, or total leaf area, but stimulated growth when combined with a complete fertilizer. Adding 1/3 leonardite (v/v) (the highest level) and a complete fertilizer increased plant height 40%, total leaf area 160%, shoot fresh weight 134%, root fresh weight 82%, shoot dry weight 133%, and root dry weight 400%.

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Xunzhong Zhang, E.H. Ervin, and R.E. Schmidt

A variety of organic materials such as humic substances, seaweed extracts (SWE), organic matter, and amino acids are being used as fertilizer supplements in commercial turfgrass management. Among them, SWE and humic acid (HA) are widely used in various biostimulant product formulations. These compounds have been reported to contain phytohormones and osmoprotectants such as cytokinins, auxins, polyamines, and betaines. Manufacturer claims are that these products may supplement standard fertility programs by reducing mineral nutrient requirements while improving stress tolerance. There is a lack of season-long, field-based evidence to support these claims. This study was conducted to investigate the influence of monthly field applications of SWE, HA, and high and low seasonal fertilization regimes on the physiological health of fairway-height creeping bentgrass (Agrostis stolonifera L.). Plots were treated monthly with SWE at 16 mg·m-2 and HA (70% a.i.) at 38 mg·m-2 alone, or in combination, and were grown under low (20 kg·ha-1/month) or high nitrogen (50 kg·ha-1/month) fertilization regimes during 1996 and 1997. Endogenous antioxidant superoxide dismutase (SOD) activity, photochemical activity (PA), and turf quality were measured in July of each year. Superoxide dismutase activity was increased by 46% to 181%, accompanied by a PA increase of 9% to 18%, and improved visual quality of bentgrass in both years. There was no significant fertilization × supplement interaction. Although not part of our original objectives, it was noted that significantly less dollar spot (Sclerotinia homoeocarpa F.T. Bennett) disease incidence occurred in supplement-treated bentgrass. Our results indicate that increased SOD activity in July due to SWE and/or HA applications improved overall physiological health, irrespective of fertilization regime. This suggests that these compounds may be beneficial supplements for reducing standard fertilizer and fungicide inputs, while maintaining adequate creeping bentgrass health.

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Erik H. Ervin, Xunzhong Zhang, and John H. Fike

High ultraviolet-B (UV-B; 290-320 nm wavelength) radiation may significantly contribute to the quality decline and death of kentucky bluegrass (Poa pratensis L.) sod during summer transplanting. Antioxidants and protective pigments may be involved in plant defense against oxidative stress caused by UV-B. Selected exogenous hormones may alleviate UV-B damage by upregulating plant defense systems. The objectives of this study were to determine if exogenous hormone or hormone-like substances could alleviate UV-B damage to `Georgetown' kentucky bluegrass (Poa pratensis L.) under greenhouse conditions. The hormone salicylic acid at 150 mg·m-2 and the hormone-containing substances, humic acid (HA) at 150 mg·m-2 and seaweed extract (SWE) at 50 mg·m-2, were applied to plugs of kentucky bluegrass and then subjected to UV-B radiation (70 μmol·m-2·s-1). The UV-B irradiation stress reduced turf quality by 51% to 66% and photochemical efficiency by 63% to 68% when measured 10 or 12 days after initiation of UV-B. Endogenous alpha-tocopherol (AT) and antioxidant enzymes (superoxide dismutase (SOD) and catalase) were reduced by UV-B stress. Anthocyanin content was increased from day 1 to 5 and then decreased from day 5 to 10 of continuous UV-B irradiation. Application of SA and HA + SWE enhanced photochemical efficiency by 86% and 82%, respectively, when measured 10 or 12 days after UV-B initiation. In addition, application of the hormonal supplements increased AT concentration, SOD, catalase activity, and anthocyanin content when compared to the control at 10 days after UV-B initiation. Bluegrass with greater AT concentration and SOD and catalase activity exhibited better visual quality under UV-B stress. The results of this study suggest that foliar application of SA and HA + SWE may alleviate decline of photochemical efficiency and turf quality associated with increased UV-B light levels during summer.

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Jerry B. Dudley, Alton J. Pertuit Jr., and Joe E. Toler

The addition of leonardite may increase, or at least maintain, production quality of ornamental plants and permit reductions in fertilizer inputs. The objective of this study was to determine the effects of a Utah-mined leonardite on early stages of zinnia (Zinnia elegans Jacq. `Small World Pink') and marigold (Tagetes patula L. `Janie Yellow') growth. The Utah leonardite was characterized by comparing it to the International Humic Substances Society's leonardite standard. Zinnia and marigold seedlings and transplants were grown in sand and 1 sand: 1 peat media (by volume) with leonardite additions of 0%, 3.125%, 6.25%, and 12.5%. Both species showed positive growth responses to 3.125% leonardite in each medium compared to fertilizer alone. Plant responses to increased leonardite additions were generally quadratic, and optimal leonardite levels were estimated. For growing zinnias, optimal conditions were determined to be 7.5% leonardite in a sand medium for seedlings and 8% in a sand-peat mixture for transplants. A sand-peat medium containing 7% leonardite was determined to be optimal for growing marigold seedlings and transplants. Addition of leonardite to growing medium offers promise for reducing fertilizer use during production of some ornamental plants.

Open access

Abdullah Ibrahim, Hesham Abdel-Razzak, Mahmoud Wahb-Allah, Mekhled Alenazi, Abdullah Alsadon, and Yaser Hassan Dewir

soil fertility, nutrient uptake limitations, and nutrient fixation ( Dada and Ogunsesu, 2016 ). Common organic-mineral fertilizers used in plant fertilization are humic substances, which contain humic acid ( Manas et al., 2014 ). Humic substances are

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Metin Turan, Ertan Yildirim, Melek Ekinci, and Sanem Argin

; Zhang and Ervin, 2008 ). Because of their unique composition, humic substances (HA and FA) promote the uptake, assimilation, and distribution of nutrients in roots and shoots that stimulate the growth of roots and shoots ( Canellas et al., 2015 ; Chen