Update 2011: Root Biology
Our research addresses whole plant growth. This work is well positioned to provide data that will target N application to the periods of maximal root activity and plant needs, determine effective and most efficient N application rates, and sustain and efficiently use land resources through improved management systems.
Planting, Treatments & Sampling in Pecan
In 2009, an experimental planting of 175 pecan seedlings was established near College Station, Texas. Root observation tubes were installed under 20 of the trees. After the soil was allowed to settle (6 months), collection of bi-weekly root observation images was initiated. These images will provide detailed information on new root production, root death, root turnover and root lifespan.
Nitrogen treatments were applied twice during the season: May & June. Eight trees were fertilized at each of the following rates: 0x, 1/4x, 1/2x, 1x, and 2x, where x is the general commercial application rate of 71.35 lbs/acre. Four trees within each N application rate had a root observation tube. Intense sampling and measurements were undertaken in 2009 and 2010.
Soil & Root Measurements
- Soil samples were taken immediately after the first N application, and again in 3, 9, and 16 weeks.
- Root samples were collected, sieved from soil, scanned for root length, and dried for tissue analysis.
- The soil surrounding the root samples was analyzed for elemental content.
Canopy & Trunk Measurements
- Images of the trees were taken bi-weekly to monitor canopy development
- Trunk diameters were measured regularly to monitor growth
- Leaf photosynthesis was measured monthly using a portable infra-red gas analyzer
Monitoring Nitrogen Movement
Twenty of the trees (five per N application rate) also received a 15N tracer to establish the movement of N from soil into plant tissue. Sampling of soil, root and leaves was undertaken and will be sent to the U.C. Davis Stable Isotope Facility for 15N analysis
Our initial results indicates that nitrogen treatment did not have a significant effect on diameter growth, net CO2 assimilation rate and water use efficiency (Table 1). There was, however, a significant effect of time of measurement (season efffects).
By taking repeated images through time, the progress of the roots can be followed as they appear, grow and eventually senesce. Our images will be processed as the project moves forward.