Identifying Opportunities for Improving Water Use Efficiency
in CA Rice Systems - 2010

 

 

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Project Leader and Principal  Investigators

Bruce Linquist, professional researcher, Dept. of Plant Sciences, UC Davis

Robert Hijmans, associate professor, Dept of Environmental Science and Policy, UC Davis

Richard Snyder, Cooperative Extension Specialist, Dept of Land, Air & Water Resources, UC Davis

Richard Plant, professor, Dept. of Plant Sciences, UC Davis

Chris van Kessel, professor and chair, Dept. of Plant Sciences, UC Davis

James E. Hill, CE Specialist, Dept. of Plant Sciences, UC Davis

 

 

 

 

In this new project a multidisciplinary team of researchers is investigating opportunities to conserve water and increase water use efficiency (WUE)—something that will be increasingly important to the rice industry, as well as other sectors of California’s economy.

The overall objective is to identify options for improving WUE for California rice systems while maintaining productivity and soil quality. The thought is “more crop per drop”—maximizing productivity for every unit of water used.

Specifically, researchers aim to develop a model for rice that can accurately predict crop growth, crop duration, water use as measured by evapotranspiration (ET), and productivity for different varieties and climatic zones in California rice growing areas. The strategy is to build on existing rice growth models developed elsewhere and adjust these for California conditions. In 2010 progress was made in the development of a database, and a preliminary “degree day” crop development model. The model examined potential water-saving benefits from later planting dates and from using shorter-duration varieties.

Database development

There is a large body of existing data available for California rice systems. One of the most valuable sources of information is the statewide variety trials conducted at six to nine locations each year on very early, early, and intermediate-to-late varieties and experimental cultivars. The Rice Experiment Station (RES) also has two planting dates in the statewide variety trials that can be used to assess the effect of planting date on crop duration and productivity.

Data from the variety trials was pulled together into a single database and continues to be refined. The data is available from 1973 to the present, with information since 1994 available in an electronic format. Information from the older trials on major varieties such as M-202 has been manually entered back to 1978.

In addition to variety trials, other information sources include:

  • A recently completed three-year project on dry- and wet-seeded rice systems included water use information on evaporation, transpiration, percolation, and drainage
  • A study on rice ET near Nicholas that was conducted by UC Davis biometeorologist Richard Snyder and retired UC Cooperative Extension farm advisor Jack Williams
  • Climate data from the California Irrigation Management Information System (CIMIS) and other weather stations around the Sacramento Valley
  • Soil data from the U.S. Department of Agriculture

Crop development model

A predictive degree-day model that estimates days from planting to 50% heading for M-202 was created from RES data from 1984 through 2009.

Degree-day accumulations are a management tool used by growers to monitor and predict the development of crop biological processes. Arkansas, Louisiana, Texas, and Missouri have developed such programs for rice. The key factor in the development of these programs is determining the best temperature thresholds for the accumulation of degree-days. These thresholds depend on the properties of local cultivars and regional climatic conditions.

Planting and 50% heading dates were taken from the variety trials at RES for M-202 from 1984 through 2009. Daily maximum and minimum temperatures for this period were downloaded from the California Department of Water Resources CIMIS station in nearby Durham. The relationship between the observed days to 50% heading and average daily temperature during this period shows clearly the effect of temperature on the rice growth cycle. From researcher evaluation of thresholds, there was a total average 1,944 degree-days to 50% heading.

Researchers tested the degree-day model on a hypothetical field planted in the Natomas area of Sutter County during the 2010 growing season—a particularly cold year with approximately 70% of the days between April 1 and July 31 below the 25-year historical average. The model estimated days to 50% heading for the 2010 season and compared it to the historical daily minimum and maximum temperatures. For a variety of planting dates from early May to late June, there was a clear delay in heading, with the greatest difference (seven days) predicted for a May 1 planting. Using only historical data, the 50% heading threshold would have been July 29 for a May 1 planting. Using a combination of historical and actual 2010 temperatures, the estimated 50% heading date was August 5. For later planting dates the difference is smaller. Researchers emphasize the estimates are conservative and larger deviations could occur.

While the model does a reasonable job at predicting time to heading based on temperature, it consistently underestimates long-duration years and overestimates short-duration years. One reason for this may be photoperiod sensitivity of the rice variety. In addition to responding to temperature, rice varieties also respond to day length. In subsequent work, photoperiod sensitivity will be accounted for in the model to increase its predictive accuracy. Also, the time from heading to maturity is affected by temperature and needs to be accounted for in the model to make it more useful to growers.

Predicting water savings

Using this preliminary model, researchers tested two options that could potentially reduce ET in rice systems:

  • Reduce crop duration by planting later in the season (when it is typically warmer)
  • Reduce crop duration by planting a shorter-duration variety (M-206 instead of M-202)

The model predicted that delaying the planting of either M-202 or M-206 from May 1 to June 1 would reduce ET by 1 inch by the 50% heading date. The model also predicted that the delayed planting date meant a difference to heading date of six days for M-206 and eight days for M-202. The shorter duration translated into a potential ET reduction of 1.6 inches, about an 8% reduction between planting and heading. The predicted difference comes without a corresponding reduction in yields.

Researchers stress that the model is still in development and needs improvement. More information is needed about how delayed planting affects development of the rice plant, panicle initiation, and grain development. This will be a focus of work on some of the major varieties in 2011.

 

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