Effect of Irrigation and Fertilization on Selected Physical and Mechanical Properties of Loblolly Pine (<i>Pinus Taeda</i>)


  • Julia Kao Hsu
  • C. S. Walters


Earlywood, latewood fertilization, irrigation, water deficits, specific gravity, growth rate, fiber stress at proportional limit, modulus of rupture, modulus of elasticity, work to proportional limit, work to maximum load


A study of the interacting effects of irrigating and fertilizing a loblolly pine plantation showed that soil moisture and ammonium nitrate fertilizer significantly affected fiber stress at proportional limit and modulii of rupture and elasticity. The effects of irrigation and fertilization on work to proportional limit were not significant and work to maximum load was affected only by irrigation. The percentage of latewood in the annual rings was found to range from 36 for wood grown on medium wet, heavily fertilized (100 lbs/acre) plots to 57 for wood grown on nonirrigated, heavily fertilized plots. The best growth rate (6.8 rings/inch) was obtained for wood taken either from the south sides of trees grown on the wettest and medium-wet plots, or from the north side of trees grown on the medium-dry plot. The strongest and stiffest wood was taken from trees grown on unirrigated plots that had received 100 pounds of ammonium nitrate per acre.

There was a positive linear correlation between percent of latewood and specific gravity, growth rate, bending strength, and stiffness. There was a similar relationship between specific gravity and the bending strength and stiffness of wood.

Maintaining soil moisture in the range of 30 to 60% of field capacity and providing a moderate amount (50 lbs/acre) of nitrate fertilizer are recommended for increasing the bending strength and stiffness of loblolly pine. Such a silvicultural practice would accelerate the growth of poles of superior strength and stiffness or pulpwood of higher fiber yield. The cost of such practices was not included in the study.


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