Golf Course Management

AUG 2019

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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08.19 GOLF COURSE MANAGEMENT 69 ing 6% iron applied at 300 pounds per acre (336.25 kilograms/hectare). e amount of each product incubated was based on the total iron content of each fertilizer as deter - mined by laboratory analysis. Soils were in- cubated for one hour and one, seven, 14 and 21 days. Immediately following each incuba - tion time, the soluble iron remaining in the soil was extracted and analyzed. Results and discussion Iron fertilizers differed in their abil- ity to remain soluble in the soil (Figure 4). Wolftrax, Vigiron, glucoheptonate, sulfate and Sweet Iron did not increase soluble iron at any time in any of the 11 soils. e che - lated iron sources increased soluble iron in the soils, and differences among chelates were primarily related to the soil pH. In general, differences between iron sources were consis - tent when measured in soils of similar pH. erefore, soils were grouped by pH ranges. Soils with pH greater than or equal to 7.9 One day after application, the only source that increased soluble iron in soils with pH greater than or equal to 7.9 was EDDHA. ese results confirm that iron chelates dif - fer in their ability to withstand displacement of their metal depending on the soil pH. Su - perintendents dealing with iron deficiency on soils with a pH greater than or equal to 7.9 have two curative options. e first option is to use EDDHA for soil applications or when foliar applications are likely to be washed off the leaves and into the soil. e second is to avoid soil applications altogether and rely strictly on foliar iron applications. Soils with pH greater than 7.0 and less than 7.9 In soils with pH greater than 7.0 but less than 7.9, only chelates EDTA, DTPA and EDDHA increased soluble iron in the soil one hour after application. Differences among chelates were small, but EDDHA was found to be superior to all other iron sources after three weeks of incubation. e ability of chelates to maintain their bond with iron changes rapidly when soil pH reaches 7.0 and above. As soil pH in - creases and approaches 7.0, iron begins to be displaced from EDTA because of increas - ing competition from calcium (Figure 5). Iron bound by DTPA may also become dis - placed, but displacement does not occur to any great extent until the pH increases to 7.5. In contrast, iron bound by EDDHA remains largely unaffected by soil pH. For these rea - sons, superintendents are advised to find out their soil pH before they decide to purchase iron chelates. Soils with pH less than or equal to 7.0 When the soil pH was less than or equal to 7.0, application of the marginal soil che - lates (citrate and IDHA) resulted in 20% of their iron remaining soluble after one hour. is means that 80% of the applied iron was not available for plant uptake. e percent - age of plant-available iron was reduced to ap- proximately 10% after one day. After a week of incubation, soils treated with IDHA con - tained the same amount of soluble iron as un- treated soil. Marginal chelates, such as iron citrate, are commonly used in foliar applications and have been shown to increase turfgrass greening when applied to turfgrass leaves. However, these results indicate that iron ap - plied as either citrate or IDHA must remain on the foliage to be effective. If the chelates are allowed to be washed into the soil, ap - proximately 90% of the iron will become in- soluble during the first 24 hours. is is in contrast to iron applied as EDTA, DTPA and EDDHA, which increased soluble iron for the entirety of the three-week study. When soil pH was less than or equal to 7.0, differ - Treatment Brand name % iron Untreated Oxide Wolftrax 58 Humate Vigiron 15 Glucoheptonate custom 6 Sulfate laboratory grade 20 Polysaccharide Sweet Iron 5 Citrate laboratory grade 22 IDHA Oligo Iron 9 EDTA laboratory grade 10 DTPA Sprint 330 10 EDDHA Sprint 138 6 Table 3. The iron products were selected because each was derived from a different iron source, and they are all available in the turf market. Experimental treatments

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