Fertilizer release from packets and its effect on tree growth.

A study was made of various factors affecting the release of fertilizer from polyethylene packets. Movement of water from the soil into the packets was almost entirely in the form of vapor and was closely related to both the area and perimeter of the pinholes in the packets. Absorption of water vapor by saturated salt solutions from air maintained near 100% relative humidity was directly related to both the solubility of the salts used and to their vapor pressure lowering values. The length of time required to release the fertilizer was directly related to the size of packet and inversely related to the number of pinholes. The more soluble fertilizer constituents were released faster than the less soluble ones. The use of packets of 19-5-17 (N, P, K) fertilizer in the field generally increased by 10 to more than 100% the rates of growth in height and diameter of cottonwood (Populus deltoides Marsh.), silver maple (Acer saccharinum L.), sugar maple (Acer saccharum Marsh.), and white ash (Fraxinus americana L.).