snyder_manganese - Correcting pH-Induced Manganese...

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Correcting pH-Induced Manganese Deficiency in Bermudagrass Turf‘ G. H. Snyder, E. 0. Burt, and G. J. Gascho2 ABSTRACT Manganese deficiency of ‘Tifgreen’ bermudagrass (Cy- nodon x rnugenissii Hurcombe) turf has been observed in South Florida when soil pH exceeded 7 as a result of irri- gation with alkaline water. A 2-year field study on Pom- pano fie sand (a siliceous, hyperthermic, typic Psam- maquent) was designed to evaluate three approaches to correcting this deficiency: 1) soil pH reduction with acid forming N sources, 2) Mn fertilization at rates up to 5 g/m* using MnSO,, a Mn-chelate, or a Mn-frit, and 3) MnSO, fertilization in combination with a series of fungi- cidal drenches for suppressing Mn-oxidizing soil fungi. Sulfate and chelate Mn sources provided short-term cor- rection of the deficiency, but little response to the frit source was noted. Sustained correction was achieved with MnSO, in combination with the fungicidal drenches. However, adequate Mn nutrition was obtained even in the absence of Mn fertilization when soil pH was maintained below 7 with acid-forming N sources. This treatment ap pears most suitable for turfgrass, since considerable N commonly is used in turfgrass production. Additional index words: Cynodon sfi., Alkaline soil. ANGANESE deficiencies are well-documented in M many plants, but few cases of Mn deficiency or responses to Mn have been reported for turfgrasses. In fact, turfgrasses are relatively insensitive to most micronutrient deficiencies other than Fe and Cu (4). Nevertheless, Mn deficiency was observed in Florida as early as 1948 (2), but the documenting evidence was not widely circulated or noted. We have observed Mn deficiency of ‘Tifgreen’ bermudagrass (Cynodon Xmagenissii Hurcombe) on several occasions at the Agricultural Research Center in Ft. Lauderdale. For example, plots receiving N from CaN [Ca(N03)2] were chlorotic and grew poorly compared to those fer- tilized with AS [(NH4)2S04] (13). Growth and color were improved when MnS04 was applied to the CaN plots, although growth remained inferior to AS plots receiving no Mn. Growth and color were nearly as good in CaN plots that received weekly fungicide drenches as in AS plots. Manganese availability is inversely related to soil pH. The oxidation of divalent Mn to less soluble forms occurs in the pH range of 7 to 8 primarily as a result of microbial activity (10). Numerous fungal species have been implicated in this transformation (Botrytis spp., Mycogone spp., Tricholadium spp., Pa- pu lospora mangan ica). Although the sand-textured Entisols and Spodosols of south Florida generally have very acid surface hori- zons, the pH of these poorly buffered soils can increase rapidly when irrigation water high in pH and calcium bicarbonate is used. In south Florida, limestone bed- rock may be found at 1 to 2 m or less in depth. Drain- ‘Contribution from the Agric. Res. Ctr., Univ. of Florida In- stitute of Food and Agricultural Sciences. Florida Agric. Exp.
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snyder_manganese - Correcting pH-Induced Manganese...

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