Sunday, May 12, 2013

I smell something ferty.

Something often forgotten is that our NPK fertilizers and recommendations are based mainly on agriculture.  Most often farmers plant multiple acres of the same crop.  The crop grows from seed to maturity in these fields, absorbing all the elements essential for plant growth from the soils.  When the crop is ready for harvest the entire plant is removed from the site leaving bare soil.  Even when fields are rotated this process happens often enough to burden the soil.  In these situations, complete fertilizers with high NPKs are necessary to replace elements robbed from the soil when plants are taken from the site.

Landscape trees and soils are managed in completely different ways.  While top soils are usually stripped and vegetation removed during the construction process, it's usually a one time event.  Most soils are still able to retain many of the elements essential for plant growth.  Trees, shrubs, and other plants also produce exudates.  Though still not fully understood, exudates promote soil micro-organisms which produce available soil nutrients over time. 

Many studies comparing fertilizers and methods of fertilization often show trees respond best to simple correct mulch applications.  Trees have evolved in forests where leaves, branches and trunks are left to decay.  Correct mulch applications mimic this dynamic.

If you suspect nutrient deficiency in a tree you're managing, it's important to identify which nutrients are lacking.  Misapplication of the wrong fertilizer can be a waste of time and money, and may hurt the tree further if one element is raised to damaging levels.

Typical Soil Analysis