Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2007
Publication Date: 4/1/2008
Citation: Altland, J.E., Buamscha, G. 2008. Nutrient Availability from Douglas Fir Bark in Response to Substrate pH. HortScience. 43:478-483.
Interpretive Summary: Substrate pH is the most influential factor affecting nutrient availability in greenhouse and nursery container mixes (substrates). While nursery growers often use lime and other materials to alter substrate pH, the impact of pH on nutrient availability in bark substrates is poorly understood. Research was undertaken to determine how modifications in substrate pH affect nutrient levels available for plant uptake. Our research documented the effect of lime application rates on substrate pH, and subsequently how pH affects availability of phosphorus and several micronutrients. It documents that increased lime rates causes an increase in bark pH, and a subsequent decrease in available phosphorus and micronutrients. Furthermore, under conditions of low pH, it documents that phosphorus levels in bark are high enough to support plant growth early in the production cycle, without amending the substrate with additional phosphorus. Phosphorus has been shown to be one of the primary pollutants from nursery and farm operations. Phosphorus from farming operations can cause eutrophication (algal blooms) in streams, lakes, and ponds. Through better pH management, reductions in phosphorus applications can be instituted in container nursery operations. This will reduce phosphorus leaching from nursery operations, especially early in the production cycle when use of water soluble phosphorus fertilizers are commonly used.
Technical Abstract: Two studies were conducted to determine the influence of substrate pH on nutrient availability in douglas fir bark (DFB). Douglas fir bark was amended with either calcium carbonate (CaCO3) or calcium hydroxide [Ca(OH)2] at 13 rates to generate substrates with low to high pH. A non-amended control was also maintained. The substrates received no other fertilizer amendments. Substrates were filled into nursery containers (2.8 L) and incubated in a nursery setting with 1.2 cm.d-1 overhead irrigation. At 1 and 6 weeks after potting, four containers of each lime treatment were harvested to determine substrate pH and availability of 13 nutrients. Substrate solutions used for analysis were obtained with the saturated media extract method. Water-extractable phosphorus, and DTPA-extractable boron, iron, copper, and aluminum decreased with increasing substrate pH. Other nutrients were either non-responsive to substrate pH, or the observed response was deemed more likely caused by calcium competition on cation exchange sites.