The two larger plots (background pines) were planted on P (phosphorous) deficient soils and P applied.
The two smaller trees in the foreground were planted at the same time on P deficient soils and no P applied.
The following information is provided by University of Georgia Warnell School of Forestry & Natural Resources: David Dickens, David Moorhead
The success of a pine plantation depends on many factors; the soil test phosphorus (P) level is one of those factors. Phosphorus fertilization is likely to be beneficial on some Coastal Plain soil such as:
1] somewhat poorly to very poorly drained, wet savannah soils
2] somewhat poorly to very poorly drained Flatwoods spodosols
3] Citronelle and associated terraces well drained heavy soils
Visit http://www.forestproductivity.net/fertilization for more information.
International Forest Co. 800-633-4506