REFINING THE RELATIONSHIP BETWEEN CANOPY LIGHT INTERCEPTION AND YIELD IN WALNUT Bruce Lampinen, Shrini Upadhyaya, Vasu Udompetaikul, Greg Browne, David Slaughter, Samuel Metcalf, Bill Stewart, Loreto Contador, Jedediah Roach, Bob Beede, Carolyn DeBuse, Janet Caprile, Bill Coates, John Edstrom, Rachel Elkins, Joe Grant, Janine Hasey, Kathy Kelley, and Bill Krueger ABSTRACT The existing mobile platform lightbar was redesigned in order to make it more robust and adjustable to a wider range of tree spacings. In addition, more accurate soil temperature sensors were added. This second generation mobile platform light bar was used during the 2011 season and performed well. In addition to the second generation mobile platform light bar, a new harvest supercart equipped with GPS, continuous yield monitoring capability, self contained hydraulics and an auto-sampler were also built with partial funding from this project. Light measurements continued on a large number of walnut orchards of varying ages and tree densities. An upper limit of about 0.05 in-shell tons per acre for every one percent of light that can be intercepted has continued to continued to be supported. When all of the walnut data from the last three years was combined, it was found that midday canopy light interception increased with orchard age until about 10-12 years when it tended to flatten and approach a value of near 93 percent. This results in a mature walnut orchard yield potential above 4 tons per acre. Work was continued on the canopy sensor suite for assessing plant water status. The results were promising and suggest the possibility of further developing this classification technique to assess plant water stress for irrigation scheduling in walnut orchards. In particular, the results using shaded rather than sunlit leaves were very encouraging and this should allow automating of the process onto the mobile platform since it is not critical to assess leaf angle for shaded leaves. PROBLEM AND ITS SIGNIFICANCE Data collected by the authors over the past several years has provided a rough upper limit to productivity in walnut and almond based on the percentage of the available midday canopy photosynthetically active radiation (PAR) that is intercepted. However, most of the data that was collected previously had limitations. The methods of measuring percent PAR interception using a handheld light bar (Decagon Devices, Pullman, WA 99163) were relatively slow and labor intensive. For this reason, much of the light bar data that was used to develop the relationship was based on sampling of relatively small samples of trees. Often the area for the yield and PAR interception data did not match (i.e. PAR data from 5 trees and yield data from either one tree or from an entire row). In the 2009 and 2010 seasons, we began using the first generation light bar for automated measurement of canopy PAR interception. In the winter of 2011, we completed the second generation light bar which was mounted on the Kawasaki Mule in the spring of 2011 and used during the 2011 summer season. The new mobile platform light bar is continuously adjustable from approximately 8-32 feet. California Walnut Board 143 Walnut Research Reports 2011
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REFINING THE RELATIONSHIP BETWEEN CANOPY LIGHT
INTERCEPTION AND YIELD IN WALNUT
Bruce Lampinen, Shrini Upadhyaya, Vasu Udompetaikul, Greg Browne, David Slaughter,
Samuel Metcalf, Bill Stewart, Loreto Contador, Jedediah Roach, Bob Beede, Carolyn DeBuse,
Janet Caprile, Bill Coates, John Edstrom, Rachel Elkins, Joe Grant, Janine Hasey, Kathy Kelley,
and Bill Krueger
ABSTRACT
The existing mobile platform lightbar was redesigned in order to make it more robust and
adjustable to a wider range of tree spacings. In addition, more accurate soil temperature sensors
were added. This second generation mobile platform light bar was used during the 2011 season
and performed well. In addition to the second generation mobile platform light bar, a new
Fig. 1. (a). Design of Kawasaki Mule mounted lightbar as used during summer 2010. Modifications included adding a branch bumper on front designed to aid in pushing through orchards with many low overhanging branches. (b)-. Over the winter of 2010-11, the entire lightbar was redesigned and rebuilt and made much more protected, robust and adjustable.
a
b
California Walnut Board 146 Walnut Research Reports 2011
has been modified in order to make it more robust and adjustable to a wider range of tree
spacings. This included rebuilding the entire light bar with a much more stable and more
adjustable base and a built in protective bumper to push low hanging branches up and over the
lightbar (Fig. 1b). A more accurate global positioning satellite (GPS) receiver and an encoder
that measures distances using the rotation of the axle were added to provide more accurate
positional information. In addition, three infrared thermometers with a much narrower angle of
view were added for measuring soil surface temperature under the tree canopy.
A load cell and GPS equipped supercart harvest trailer was also built with partial funding from
this project (Fig. 2). The trailer has self-contained hydraulics to operate the augers and rear
elevator as well as an autosampler. This allows the trailer to be used with almost any grower
harvesters since we do not need to match the hydraulic hookups to the growers equipment. The
trailer also allows our experimental harvest plots to be picked up and weighed on a continuous
basis with minimal disruption to grower harvest operations since we can offload the nuts into any
type of bank out system the grower uses. The yield data from the load cells on the trailer is
logged 10 times each second to the Trimble GPS unit which allows continuous yield data to be
compared to continuous light bar data.
Fig. 2. Load cell and GPS equipped supercart built with funding from this project.
This setup allows us to collect continuous yield data which is then logged to the
Trimble GPS unit.
Objective 2
A total of 28 orchards were mapped in 2011 (Table 1). Midday canopy light interception varied
from about 10 to 90 percent in the orchards studied in 2009-2011 (Fig. 3). Several of the
orchards were above the line in 2009 but in general, where these same orchards were measured
again in 2010 they tended to be below the line. Past data has suggested that alternate bearing may
allow orchards to rise above the line in one year but will then tend to be below the line in the
California Walnut Board 147 Walnut Research Reports 2011
following year. Yield data was lost at several sites in all years due to problems with scheduling
harvests with growers and/or due to early fall rains making plot harvest difficult to fit within the
grower harvest schedule.
Measurements were also done throughout the season on an eight year old Howard pruning trial
in 2010 as well as a three year old Chandler/Tulare/Forde/Gillet pruning trial at Nickels Soil
Laboratory in Colusa County in 2010 and 2011. Midday canopy light interception was fairly
constant through the season for the more mature Howard pruning trial shown in Fig. 4. This
Lake Walnut lightbar sites Lake County- Upper LSutter Walnut lightbar site Rio Oso #2Sutter Walnut lightbar site Rio Oso #1San Joaquin Tulare Farmington siteStanislaus Chandler site ModestoYolo County Chandler site MadisonYuba Tulare Surround trialColusa Nickels Howard pruning trial
6Sutter Walnut lightbar site Rio Oso #2Sutter Walnut lightbar site Rio Oso #1San Joaquin Tulare Farmington siteYolo County Chandler site MadisonNickels Howard unprunedNickels Howard unpruned + nut removalNickels Howard prunedNickels Howard pruned + nut removalNickels Howard pruned 2006, hedged 2008Nickels Forde unpruned, unheadedNickels Forde moderately prunedNickels Forde heavily prunedNickels Gillet unpruned, unheadedNickels Gillet moderately prunedNickels Gillet heavily prunedNickels Tulare unpruned, unheadedNickels Tulare moderately prunedNickels Tulare heavily prunedRio Oso Orchard #3Solano Surround trial untreated controlSolano Surround trial Surround treated
2010
2011
Midday canopy light interception (%)
0 20 40 60 80 100
Yiel
d (d
ry to
ns/a
cre)
0
1
2
3
4
5
6 San Joaquin Tulare Farmington Site Yolo County Chandler site MadisonNickels Howard unhedgedNickels Howard skirtedNickels Howard hedgedNickels FordeNickels GilletNickels TulareNickels Chandler minimal prunedNickels Chandler untrained, unprunedNickels Chandler heavily prunedNickels Chandler minimal pruned plus deficitMature Chandler Lake CountyLake County 10 yr old ChandlerLake County 9 yr old ChandlerRio Oso Chandler #1Rio Oso Chandler #2Tehama mature Chandler #1Tehama mature Chandler #2Tehama 5 year old ChandlerTehama 6 year old ChandlerColusa 14 yr old Howard Orchard #1Colusa 14 yr old Howard Orchard #2
Fig.3. Midday canopy light interception versus yield relationship from various walnut trials
from throughout state measured with the Mule mounted light bar in 2009, 2010, and 2011.
California Walnut Board 148 Walnut Research Reports 2011