Identifying Opportunities for Improving Water Use Efficiency in California Rice Systems, 2014


Project Leader

Bruce Linquist, UCCE rice 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 2014 research were to continue work on a crop development model for moderately photoperiod sensitive varieties such as M-202 and M-206 and to determine how crop management practices affect the crop development model. Salinity accumulation in no-spill systems, while not an explicit objective, was another area of study.

Crop model development

Previous research suggested that some varieties might be moderately photoperiod sensitive. However, a greenhouse study found that most tested varieties (CM-101, M-104, M-105, M-202, M-206, S-102, and L-206) were not photoperiod sensitive. The exception was M-401, which is photoperiod sensitive. Thus, crop development is expected to be governed by degree-day accumulation. A thermal-time model was developed and data from statewide variety trials was used to calibrate and validate the model. The model accurately predicts time to panicle initiation, heading, and physiological maturity. This model will be developed into an online tool that growers can use in crop management decisions.

Management and crop development

In 2013 and 2014, field trials were conducted at the Rice Experiment Station to determine the effect of water temperature and management on crop development. An experiment evaluating alternate wetting and drying was used for this study.

Treatments included wet-seeded continuous flood, wet-seeded with intermittent wet and dry periods following canopy closure, and drill-seeded with intermittent wet and dry periods throughout the season.

Results were similar in both years of the study. Panicle initiation, heading, and physiological maturity were delayed in the drill-seeded treatment by three, six, and eight days, respectively. There was no difference in the other treatments. This suggests that water management—perhaps because of differences in air and water temperature—plays an important role in rice development and degree-day accumulation. Water temperature data from this study will be incorporated into the model.

Salinity in no-spill systems

Water restrictions because of drought conditions in 2014 provided an opportunity to evaluate no-spill water management for salinity buildup and yield.

Six fields were monitored during the 2014 growing season: one field each in Butte and Yuba counties, and two fields each in Colusa and Glenn counties. In each field, salinity was measured in the first, middle, and bottom checks. Three plots were established in each check: one close to the water inlet, one in the middle, and one at the farthest point from the water inlet. During the growing season, water and soil electroconductivity (a measure of salinity), water height, water and soil temperature, and plant height at panicle initiation were measured on a biweekly basis.

Preliminary results show that, as expected, lower salinity values were found in the top checks and the highest were in the bottom checks. Soil salinity values were higher than in floodwater. Soil salinity values increased early in the season and then decreased and leveled off for the last part of the season.

Some fields had salinity levels above the point of critical sensitivity to rice. However, this had no apparent effect on grain yield. The data from six fields suggest that if a field receives clean water with low salinity that yields will not be compromised.