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Effect of Soil Mixtures and Irrigation Methods on Leaching of N in Golf Greens¹

Utilization of applied N by ‘Penncross’ creeping bentgrass (Agrostis palustris Huds.) is of special interest because of the cost and availability of N and the potential environmental problems resulting from its deep percolation. The influence of soil mixtures, irrigation systems, and N sources on N leaching was studied in experimental, though functional, golf greens from 1973 to 1976. Sprinkler irrigation was compared with subsurface irrigation using porous irrigation tubing constructed from spun-bonded olefin. Soil mixtures contained from 60 to 80% sand and variable amounts of silt loam topsoil, calcined clay and humus. Nitrogen treatments included activated sewage sludge, ureaform, ammonium nitrate, 30% N solution, anhydrous ammonia and nitrapyrin. Nitrogen solutions were applied through the subsurface irrigation system while other N carriers were surface applied. Each soil x irrigation treatment was underlain by a drainage line placed in pea stone at a depth of about 46 cm. Water samples were collected periodically from drainage lines and analyzed for NH₄- and NO₃-N.

Nitrogen leached primarily as NO₃-N with a reduced rate of loss associated with slow release N sources and the onset of low seasonal temperatures. Even though about 75% of the added was NH₄-N, N solution (30% N) applied through the subsurface irrigation system caused a sharp increase in NO₃-N in the drainage water. Anhydrous ammonia with or without nitrapyrin reduced NO₃-N leaching losses for 1 to 2 weeks but had little effect on the average NO₃-N concentration over a 47-day period.

Subsurface irrigation stimulated turfgrass growth in bands about 20 cm wide located above the irrigation lines. Appearance of growth bands was associated with low temperatures and increased levels of NO₃-N in proximity to the irrigation lines. Banding was most apparent in soil mixtures containing low levels of residual soil N and absent when turfgrass was adequately fertilized with N.

Key Words: Subsurface irrigation • Bentgrass • Nitrapyrin

² Extension agronomist and professor, associate professor, associate professor, research assistant, and graduate student, respectively, Dep. of Plant Science, Univ. of Delaware, Newark, DE 19711.

Received for publication July 1, 1976.