Effects of Compost on Loblolly Pine Growth

By Craig Coker, Vice President
Mountain Organic Materials, LLC

Stuckey, H.T. and Hudak, P.F., “Effects of Compost on Loblolly Pine Tree Growth in Northeast Texas ”, Compost Science and Utilization, Vol. 9, No. 1, Winter 2001, p. 65-72

The objective of this two-year study by the University of North Texas was to evaluate the effects of compost on loblolly pine (Pinus taeda) tree survival, growth and soil moisture.  Loblolly pines are the main softwood source in the southeastern U.S.

Over 700 Loblolly pine seedlings were planted on a ¾ acre site in March 1997 near Daingerfield, Texas, on sandy loam soils with pH levels between 6 and 7.  The study area has long, hot summers and short, mild winters.  Average annual rainfall is approximately 45 inches.

Twenty (20) cubic yards of compost was applied to the site.  The compost was produced from yard trimmings, pallets, lumber, bread, dough, vegetables, brewery waste, and rhinoceros and elephant manure from the Fort Worth Zoo.  

Upon delivery, it had a pH of 7.5 and a 1.3 percent total nitrogen content.  Compost was applied at rates of 0, 5, 25, and 50 tons per acre. Two experimental designs were used: half the trees had compost incorporated into the backfill soil around the tree roots followed by topdressing with compost, while the other half used native soil to backfill around tree roots, but had a compost topdressing applied.  

Tree height and diameter were monitored monthly.  Cumulative rainfall was close to the annual average in each year of the experiment. However, periodic drought conditions persisted during the initial summer months. 

The 25-ton per acre application with soil backfill (25S group) increased tree survival and growth relative to the control group (the zero ton/acre group).  After two years, trees in this group survived twice as much and grew 41% higher than the control group and grew the most among all the trees in the compost-amended plots.  

The authors conclude that the compost topdressing over the soil backfill in the 25S group allowed the compost to move to the roots more gradually and accelerated growth.  

They observed that a 25-ton per acre application yielded more growth than a 50-ton per acre application  which they concluded was due to the formation of soil conditions in the high application group that deviated too much from the normal soil conditions for growing loblolly pines in northeast Texas.

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