Golf Course Management

APR 2014

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98 GOLF COURSE MANAGEMENT 04.14 cumulation of organic matter at the surface that generally decreased with depth (uncon - frmed for Southeast 2, which did not feature the upper approximately 8 inches of the pro - fle). Below a depth of 3 to 5 inches (2.6-12.7 centimeters), organic matter content of the root zones was relatively low. However, accu - mulations of organic matter in the cemented layers near the sand/gravel interface were evi - dent at each site, suggesting that organic mat- ter mobilized and accumulated at the textural boundaries. Organic matter accumulation could negatively affect subsurface drainage and potentially result in greater water reten - tion at the sand/gravel interface, thereby ex- acerbating iron and manganese cementation. How do t ese layers form? The layers described in this study qualify as "placic horizons," which are thin black to dark reddish pans cemented by iron and/or manganese and organic matter (7). Placic horizons form in a three-step process: (a) mineral Fe(III) is reduced to soluble Fe(II); (b) reduced Fe(II) is translocated downward in the profle; and (c) reduced Fe(II) is re- oxidized to Fe(III) at textural boundaries or areas where pH increases dramatically (3). The layers described in this study form in the same three-step process, but do so much more quickly than in natural soils because of management-related inputs of iron from fer - tilizer and irrigation and the abrupt textural boundary where the sand root zone meets the gravel drainage layer. In the feld, we have observed iron-cemented layers in root zones as early as fve years after construction. In natural soils, placic horizons only form in areas with high annual precipitation (1). Our fndings suggest that in putting greens, the occurrence of these layers does not appear to be restricted to certain climatic or geographic regions, likely because of irrigation. Acidic pH conditions increase iron mobil - ity by favoring Fe(II) (2), and the pH values reported in Table 2 tell an interesting story. We observed three general scenarios with soil pH: (a) pH was acidic throughout the ma - jority of the profle (Northeast); (b) pH was acidic or neutral throughout the profle and became alkaline near the sand/gravel inter - face (Midwest and Southeast 2); or (c) pH was neutral or alkaline and became acidic near the sand/gravel interface (Southeast 1 and Oceania). In the frst scenario, acidic pH favors the more soluble Fe(II), which is read - ily mobilized to the textural boundary where it oxidizes in the presence of O 2 below. The second scenario is similar to the frst, but as Figure 4. Profle from Midwest, which featured zones of iron accumulation at the lower interface of an organic-rich surface layer (3.5 inches [9 centimeters]) and at the sand- gravel interface (14 inches [35.5 centimeters]). Figure 1. Close-up of a manganese oxide-cemented layer from Southeast 2. Figure 2. Iron oxide-cemented layer at the sand-gravel interface from Oceania. This layer had formed within less than fve years after construction of the putting greens. Figure 3. Close-up of iron-oxide layer at the lower inter - face of an organic-rich surface layer (~4-inch [10-cen- timeter] depth) from Northeast. This layer was acting as a barrier to root growth. There was also a layer at the sand-gravel interface (not shown). 090-101_April14_TechwellCuttingEdge.indd 98 3/18/14 2:54 PM

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