Abstract
Phosphorus is widely deficient throughout the southern pine region of the United States. Growth responses to P fertilization are generally long-lasting in a wide range of soil types, but little is known about fertilization rates and long-term P cycling and availability. In 1982, exceptionally high P fertilization rates (0, 81, 162, and 324 kg P ha−1) were applied to a loamy Ultisol in central Louisiana, USA. We measured vegetation responses at age 27 years and sequentially extracted soil P to 1 m to elucidate potential P availability into the next rotation. Loblolly pine responded well to the lowest fertilization rate; total biomass was 39% greater in the fertilized plots compared to the unfertilized plots, but higher fertilization rates had no effect, presumably due to induced N-limitations. What little fertilizer P was found in the soils was in the moderately labile NaOH fraction in the surface 20 cm, and may be slowly available to the next pine rotation. Normal rates of P fertilizer will maintain elevated available P well into a second rotation in loamy Pleisteocene Ultisols of the western Gulf Coastal Plain. Exceptionally high rates were not effective at increasing potentially available P beyond normal rates.
Highlights
The looming global P shortage [1] places a premium on understanding the most efficient use of P fertilizer to maintain productivity without squandering this vital resource for future food and fiber needs
Previous research in the Atlantic Coastal Plain of the United States resulted in guidelines to help determine P deficiency [2,3], and it has been widely reported that many lower and upper Coastal
The somewhat poorly drained Beauregard soil was characteristic of the low P, Pleistocene-age terraces of the western Gulf Coastal Plain
Summary
The looming global P shortage [1] places a premium on understanding the most efficient use of P fertilizer to maintain productivity without squandering this vital resource for future food and fiber needs. Previous research in the Atlantic Coastal Plain of the United States resulted in guidelines to help determine P deficiency [2,3], and it has been widely reported that many lower and upper Coastal. Plain soils are P deficient and respond to P fertilization at establishment [4]. Coastal Plain, soils developed from Pliocene deposits known as the Citronelle and related formations are widely known to be deficient [4]. Pleistocene-age terraces may not be as broadly deficient as Citronelle terraces but frequently respond to P fertilizer both at establishment and again at midrotation if accompanied by N additions [5].
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