Identifying Opportunities for Improving Water Use Efficiency, 2017

 

Project Leader

Bruce Linquist, UCCE specialist, Dept. of Plant Sciences, UC Davis

The goal of this project is to identify opportunities to conserve water in California rice systems. Objectives of 2017 research were:

  • Determine how water temperature affects crop development.
  • Complete analysis of salinity research and develop salinity management guidelines.
  • Initiate studies on groundwater levels and implications for irrigation management.

Salinity and water temperature research

Research on salinity has been completed. Peer reviewed research can be viewed in Agricultural Water Management, 195:37-46, Spatial-temporal salinity dynamics and yield response of rice in water-seeded rice fields. Information from this study is being developed into a handout and should soon be available to growers.

Research examining water temperature effects on crop development has been submitted for publicaiton in Paddy, Water and Environment. In brief, this research indicated that crop development from planting to panicle initiation (PI) was more sensitve to water temperature than air temperature. Development rates from PI to maturity were best predicted by air temperature. Based on these findings, degree day models to predict crop developmental stages would be improved by using water temperatures during the first part of the growing season.

Percolation and seepage losses

Direct measurements of percolation losses were made in eight fields spread throughout the Sacramento Valley. Percolation rates ranged from 0.02 inches to 3 inches per season, assuming 120 flooded days. The average percolation rate across all sites was about 1 inch per season.

In general, lateral seepage losses were small but highly variable. The highest lateral seepage losses recorded would amount to only 2 inches per season for a 100-acre square field bordered completely by that type of levee. Seepage was greatest for levees that bordered a drainage ditch, followed closely by those that bordered fallow fields. Seepage was a water input to the field for some levees bordering higher flooded fields or supply canals, though this wasn’t true in all cases. Ongoing work is looking at the influence of factors such as levee type and dimension, field water height, and soil texture.

Water balance

A complete water balance was calculated for three sites. Tailwater drainage was measured with an outlet weir and data loggers that recorded the height of water above the weir crest. Irrigation inputs ranged from 4 feet to 5 feet, while evapotranspiration averaged 2.5 to 2.75 feet. Tailwater drainage—including maintenance flow, herbicide application drains, Leather’s drains (if applicable), and the final drain for harvest—ranged from 4 inches to 25 inches. Lateral seepage and percolation together were about 2 inches or 6% of evapotranspiration, which is lower than previously estimated.

Thus, evapotranspiration accounted for approximately one-half to two-thirds of the applied water, with tailwater drainage representing the second largest outflow. Percolation and lateral seepage account for a very small amount of the applied water.