Update 2011: Soil Controls on N & Water Uptake
Initial Results for Two Years (2009-10)
The first two seasons of data collection have been completed. Soil Water Depletion (SWD), a root zone measurement of the amount of water within the soil, is an indicator of water stress within the tree. SWD measurement throughout the season supports the following conclusions:
- Soil Water Depletion (SWD) varied with soil depth
- SWD within the rootzone was higher in the shallow depths where Root Length Density was also higher than in the deeper depths.
- The SWD at site 1 was higher compared to site 2 due to the higher clay content in the soil at site 2: Soil texture at site 1 was sandy loam, with sand at the lower depths. Soil texture at site 2 was silty clay loam.
- The SWD patterns at outside the tree driplines were similar to those under-canopy locations because of similar RLD at the shallow depths.
- SWP at 2.5 m height, 4.5 m, and 7.6 m decreased with increasing tree height, and decreasing soil water content at different depths, which were significantly correlated with SWP.
- The decrease in SWP at 2.5, 4.6, and 7.6 m heights was because of the increase in midday atmospheric VPD
- Significant combined influence of soil water content and midday air temperature on SWP indicated that these parameters can be used as an adjunct for interpreting SWP to help refine irrigation scheduling
Initial results in this ongoing project have improved our understanding of stem water potential, its dependence on height, and strong correlation to soil water content.