SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
Issue link: http://read.dmtmag.com/i/306114
www.stma.org May 2014 | SportsTurf 21 nated with metals by industrial processes. It is hypothesized that these hyperaccumulators evolved to exploit high soil Ni concentrations to enhance plant defenses from herbivory and disease. Ni NutritioN aNd urea NitrogeN MetabolisM Nickel is a highly mobile element in the plant due to chelation with organic molecules and tends to accumulate in newly formed tissue. Several enzymes in biological systems require Ni as a catalyst; however, the most well-known role of Ni in plant metabolism is its function in the activation of the enzyme urease. Urease hydrolyzes (breaks down) urea into ammonia and carbon dioxide. The hydrolysis of urea by the Ni dependent enzyme urease is necessary to make the nitrogen (N) in urea available to plants. Urease cannot work if it is not accompanied by Ni. Urea is the most popular N source in management due to its solu- bility, high percentage of N, low price, and ease of handling. Urease and Ni are also important for plants being fertilized with other N sources (nitrate and ammonium) because of the need to cycle urea generated as a byproduct of metabolic processes within the plant. Nickel deficiency has been recorded in several species and leads to an accumulation of urea in leaf tissue causing toxicity, foliar burn, and inefficient urea-N use. Research has determined that plants can directly absorb urea through urea specific channels and aquaporins (water channels found in cell membranes), which changes the previously hypothesized view that urea-N was absorbed by the plant only after being hydrolyzed by urease in the soil or plant surface. Soil urease inhibitors have been thoroughly researched and employed to limit gaseous N loss by ammonia volatil- ization after hydrolysis. However, the directly absorbed urea from leaf surfaces is directly hydrolyzed by urease in the plant tissue before being assimilated into organic N containing compounds. CurreNt researCh Research conducted at Clemson University reported increases in urease activity, amino acid content, and growth of 'Diamond' zoysiagrass and 'TifEagle' bermudagrass fertilized with foliar urea and supplemental Ni. Plants not receiving supplemental Ni con- tained <1 ppm Ni in leaf tissue, whereas Ni supplemented plants accumulated up to 17 ppm by the conclusion of the study. At this concentration, no toxicity symptoms were observed. In a second study at Clemson University, Ni toxicity was examined in the same species. Symptoms of toxicity progressively increased as Ni concen- tration reached 100 ppm and resulted in growth reductions up to 32% in 'TifEagle' at the highest Ni concentration supplied. Due to these findings, 'Diamond' and 'TifEagle' are considered moderately tolerate of Ni and further research should be conducted to measure the effects of Ni supplementation and toxicity of other commonly used turf species. Future prospeCts Not much is known about other roles Ni plays in the plant and current research is lacking in most agricultural crops including turfgrass. However, from the limited research already conducted, increases in growth and plant health with supplemental Ni nutrition have been recorded. Future research is required due to the popu- larity of urea as an N source in turfgrass management and strong relationship with the Ni containing enzyme urease that makes the N available to the plant. Further, several questions have been raised concerning Ni nutrition and turfgrass management: Can turf be established more quickly (seeding, sprigging) when supplemental Ni is applied? Are there synergistic effects with pesticides to reduce total inputs and improve plant health? What are the long-term ecological impacts of Ni supplementation? Can Ni supplementation improve urea N use efficiency and does it improve foliar uptake? Can increased Ni concentration in foliage inhibit herbivory? Is there enough Ni bioavailable for turfgrasses that supplementation is not necessary? Currently, no Ni fertilizer sources are marketed for turfgrass, while other micronutrients with similar concentrations within the plant (Mo) are commonly included in liquid micronutrient products. Only one Ni fertilizer is currently marketed (Nickel Plus, Nipan LLC.) for use in pecan. To investigate Ni nutrition and possible turfgrass deficiency, an estimate of Ni input needs to be determined for managed turfgrass surfaces. Additional research determining bioavailability in turfgrass scenarios also needs to be conducted to examine if Ni supplementation would be beneficial. ■ Dr. Nick Menchyk is Postdoctoral Fellow, School of Agricultural, Forest & Environmental Sciences, Clemson University. Dr. Dara Park is Assistant Professor, School of Agricultural, Forest & Environmental Sciences, Clemson University. Dr. Haibo Liu is Professor, School of Agricultural, Forest & Environmental Sciences, Clemson University References for this article can be found on www.sportsturfonline.com. Nickel nutrition • Very little is known about Ni nutrition and fertilization of turf- grasses. • Due to the extensive use of urea and the necessity of Ni in urea N metabolism, further research is required to determine best management practices for foliar urea N fertilization and supplemen- tal Ni fertilization. • Increased leaf tissue growth due to Ni supplementation was observed in 'Diamond' zoysiagrass and 'TifEagle' ultradwarf ber- mudagrass during research at Clemson University. • Nickel is an essential plant micronutrient • The reduced Ni bioavailability in common turfgrass manage- ment scenarios requires further research to determine Ni sufficiency and deficiency ranges • Nickel is required for functional urease activity in plants • Urease is a Ni dependent enzyme that hydrolyzes urea making the N available to plants • Urease and Ni are important in the cycling of urea generated within the plant and can reduce urea toxicity (foliar burn)