Production of the UC Leaf Color Chart, 2015

 

Project Leader

Randall "Cass" Mutters, farm advisor, UC Cooperative Extension, Butte County

The objectives of this project were to fabricate, assemble, and distribute 2,000 copies of a new UC Leaf Color Chart (LCC) to rice growers and allied agricultural professionals. The color chart can be used in on-farm nitrogen management decisions to help meet discharge requirements under California’s irrigated lands regulatory program.

The original UC Leaf Color Chart was created in 2000. At that time 1,500 copies of the LCC were produced. The LCC was distributed to rice growers, PCAs, and allied agricultural professionals throughout the Sacramento Valley. No additional production has occurred since that time. With inventory low—and the need to meet the required nitrogen management plan requirements for rice—a new production run of the LCC was initiated. In this project, careful attention to quality was taken to ensure that newly fabricated leaf color charts would be identical in color characteristics and as durable as the original.

The colors of the individual plates on the original leaf color chart were derived from the spectral reflectance signature of rice leaves in a range of leaf nitrogen contents. The actual leaf color was captured with a spectrophotometer, and the resulting color descriptors were used to formulate the colors used in construction of the leaf color chart.

In this project, researchers worked with Techmer PM of Rancho Dominguez to spectro-analyze and digitally render the individually unique colors to ensure that the next-generation leaf color chart reliably describes the actual color of a rice leaf. The resulting data were used to formulate high temperature resistant, UV stabilized, colorized acrylic plastic. Test plates were created to compare with the original leaf color chart. The process was repeated until the colored plastic matched the original leaf color chart. Once the formulation was complete, colorized nonreflective acrylic plastic pellets were manufactured for use in an injection molding process.

The new leaf color charts were manufactured and assembled by a Chico company, WREX. The Chico State School of Engineering created schematics describing individual components.

The new leaf color charts were delivered in April 2016. The new charts are different in one important respect. The lightest colored cell from the original leaf color chart has been omitted and an additional darker green cell has been added to accommodate varieties with darker leaf color. The total number of color cells remains unchanged at eight.

The new leaf color chart will be calibrated with a nitrogen by variety experiment at the Rice Experiment Station during the 2016 growing season. Leaves from selected California rice varieties grown with different levels of fertilizer nitrogen will be sampled. Leaves will be laboratory analyzed for total nitrogen. Results will be correlated with the color cells in the leaf color chart to produce a calibration curve and table that will be included with all new leaf color charts.