Agronomy Journal • Volume 106, Issue 2 • 2014 585 soil Fertility & crop nutrition Perennial Ryegrass Growth Responses to Mycorrhizal Infection and Humic Acid Treatments Ali Nikbakht, Mohammad Pessarakli,* Naghmeh Daneshvar-Hakimi-Maibodi, and Mohsen Kai Published in Agron. J. 106:585–595 (2014) doi:10.2134/agronj2013.0275 Copyright © 2014 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. ABstRAct Arbuscular mycorrhizal (AM) symbiosis confers numerous benefits to host plants, including improved plant growth and nutrient acquisition efficiency. An experiment was conducted to evaluate the effect of AM fungi ( Glomus intraradices and G. mosseae) in the presence of humic acid (HA) spray treatments (0, 100, 400, and 1000 mgL –1 ) on nutrient (N, P, K, Fe, and Zn) uptake, visual quality and chlorophyll content, root growth and architecture, and colonization of perennial ryegrass (Lolium perenne L.) Speedygreen mixture. e results revealed that HA did not affect plant growth significantly; instead arbuscular mycorrhizal fungal (AMF) colonization improved dry and fresh weights. Mycorrhizal inoculations significantly increased visual quality (13 and 15% in inoculated plants compared to non-inoculated ones) that might be at least partly due to elevated total chlorophyll content. e AM inoculation and HA treatment resulted in improved root architecture rather than root biomass production. Neither HA treatments nor mycorrhizal inoculation affected N and Fe contents of the leaves; however P, K, and Zn concentrations improved by AM inoculation. More roots were colonized by G. intraradices than by G. mosseae. ese results suggest that AM inoculation is beneficial in enhancing uptake of some nutrients and root development of ryegrass possibly leading to less fertilizer input and more drought resistance. A. Nikbakht, Dep. of Horticulture, College of Agriculture, Isfahan Univ. of Technology, 8415683111 Isfahan, Iran; M. Pessarakli, School of Plant Sciences, College of Agriculture and Life Sciences, he Univ. of Arizona, Tucson, AZ 85721; N. Daneshvar-Hakimi-Maibodi, and M. Kai, Dep. of Horticulture, College of Agricultural Science and Engineering, Campus of Agriculture and Natural Resources, Univ. of Tehran, Karaj, Iran. Received 8 June 2013. *Corresponding author (pessarak@ag.arizona.edu or pessarak@ email.arizona.edu). Abbreviations: AM, arbuscular mycorrhiza; AMF, arbuscular mycorrhizal fungi, mycorrhiza fungi; Chl, chlorophyll; HA, humic acid; HS, humic substances. Under natural conditions, about 90% of all plant species form a symbiotic association with mycorrhizal fungi (AMF) (Smith and Read, 1997; Brundrett, 2002). Arbuscular mycorrhizal symbiosis provides many beneits to host plants, including enhanced plant growth (Kim et al., 2010), mineral nutrition (George, 2000), resistance to abiotic stresses, includ- ing drought (Auge, 2001, Abbaspour et al., 2012) and salinity (Shari i et al., 2007) when compared to similar noncolonized (Non-AMF) plants. Most grasses form an AM symbiosis (Newman and Reddel, 1987). However, very few studies are available on AM symbiosis of turfgrass species. Also, turfgrass is oten grown under improved maintenance conditions. It has been hypothesized that these plants are less dependent on mycorrhizae and AM symbiosis and that such symbiosis would beneit them less than other species (Pelletier and Dionne, 2004). Butler and Hunter (2008a) reported that application of seaweed extracts and microbial inoculants treatments into the root zone of creeping bentgrass (Agrostis stolonifera L.) signi icantly alleviated stress tolerance. Pelletier and Dionne (2004) showed that a lawn mixture of Kentucky bluegrass (Poa pratensis L.), red fescue (Festuca rubra L.), and perennial rye- grass (Lolium perenne L.) inoculated with Glomus intraradices established more quickly than Non-AMF turfgrasses. Similar results were shown when the grass was inoculated with G. etu- nicatum. Our preliminary results also showed that perennial ryegrass was successfully colonized by mycorrhizal species and afected by the AM symbiosis (Kai et al., 2013). However, many commercial products consisting of humic substances (HS), including humic acid (HA) and fulvic acid (FA) have been recommended for use on turfgrasses (Liu and Cooper, 2000). Humic acid is the main fraction of HS and the most active component of soil and compost organic matter (Ferrara et al., 2007). hese compounds have many beneits such as phyto-hormone-like activity (Pizzeghello et al., 2001; Fike et al., 2001) that directly and indirectly have stimulating efects on the physiological processes of plant growth (Yang et al., 2004). Several researchers have noted that foliar application of HA positively afects plant growth. In this respect, there are efects on uptake of nutrients (Adani et al., 1998; Tejada and Gonzalez. 2003), photosynthesis (Liu et al., 1998), increasing root growth (David et al., 1994) and enhancing seed germination and seedling growth (Dorer and Peacock, 1997). he use of HA has oten been proposed as a method to improve crop production (Nikbakht et al., 2008). However, these materials have become the most commonly used organic materials in golf course turf management Published March 6, 2014