Lawn Fertilizer Effects On Tree Leaf Mulching.

Mulching deciduous tree leaves into turfgrass with a lawnmower has grown in practice as a way to effectively compost autumn leaf waste. As the effects of fertility on mulching were unknown, tests were conducted to determine whether applying lawn fertilizers to mulched tree leaves could accelerate leaf decomposition over time. Field studies were conducted at Michigan State in 2007 and at both Michigan State and Scotts in 2008 to measure the effects of fertilizer applied to two depths of mulched tree leaves. Dry tree leaves applied at rates of 15.2 cm (low) and 45.7 cm (high) were mulched into plots of established mixed turfgrass maintained at a height of 7.6 cm. Fertilizer treatments in 2007 included a 29-2-3 at 43.9 kg ha^-1 and a 22-2-14 at 30.3 kg ha^-1, and in 2008 a 22-2-14 at 39.4 kg ha^-1 was used. Fertilizers were applied after final mulching in Nov to early Dec depending on site and year. Spring evaluations in both years showed all fertilizer treatments significantly reduced visible leaf mulch in the high leaf rate vs. the unfed controls. Fertilization had no effect on the low leaf rate. We believe mulching alone is sufficient to incorporate this low rate of leaves into a turfgrass canopy and thus the addition of fertilizer may not provide noticeable benefits. Results from this study suggest late fall lawn fertilization may be a useful strategy for accelerating leaf decomposition when mulching large amounts of leaves.