Role of Foliar Iron in Alleviating Root Growth Inhibition of ‘Penn A-4' Creeping Bentgrass (Agrostis stolonifera L.) Induced by Intensive N Fertilization.

Intensive N fertilization of creeping bentgrass (Agrostis stolonifera L.) putting greens encourages excessive shoot growth while potentially limiting root growth. Field experiments investigated partial substitution of N by iron in fertility programs of ‘Penn A-4’ creeping bentgrass managed as putting greens. Either sand- or soil-based putting greens were treated with combinations of iron at rates of 0 to 4.9 kg ha^-1 mo^-1 (as FeSO₄∙7H₂O) and N at rates of 14.6 to 43.9 kg ha^-1 mo^-1 (as NH₄NO₃), every 6 or 12 d, May to Oct. 2007. Turfgrass color, canopy density, clipping yield, tissue nutrient levels, root length density (RLD), specific root length, and root mass were measured to evaluate growth and visual quality. Extreme N levels reduced RLD, while the highest N rates were more detrimental to root growth than the lowest ones. The highest RLD was observed at the highest iron rate in combination with medium N rates. Foliar iron applications appeared to benefit Penn A-4 creeping bentgrass root growth, especially under intensive N fertilization programs.