Identifying Opportunities for Improving Water Use Efficiency in California Rice Systems, 2015

 

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. Specific objectives for 2015 research:

• Develop an online tool that can estimate time to panicle initiation, heading, and maturity.

• Determine how drill seeding and water temperature affect crop development.

• Quantify floodwater and soil salinity variation across fields and time.

• Evaluate rice varieties for tolerance to salinity in pot and field studies.

Crop model development

Developing a model to accurately predict crop development has been one of the objectives of this project for several years. Research into the time required to reach various crop development stages was completed in 2014.

In 2015, an online tool was developed that will allow producers to estimate the time to panicle initiation, heading, and maturity. Users select a weather station, variety, and planting date. The current model works with varieties CM-101, M-104, M-105, M-202, M-205, M-206, S-102, and L-206. Crop development is expected to proceed based on the accumulation of thermal time or “degree day” accumulation. The model can be accessed at the University of California Rice On-line website at rice.ucanr.edu. Link to DD Model/Crop development.

Water temperature effects

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.

In another study, various M-206 fields in Butte County receiving cold water were identified. Transects were set up to monitor soil, water, and air temperature with sensors located at the inlet to the first check. At each sensor, the date of panicle initiation, heading, and maturity were determined. Results are still being evaluated. This work will be finalized in 2016.

Salinity in no-spill systems

The drought of recent years has resulted in some water districts requiring no-spill water management. Given interest in evaluating opportunities to reduce water use, research was begun in 2014 to evaluate the impact of no-spill water management on salinity buildup and yield. This research expanded in 2015 with different fields under both no-spill management and continuous flow-through systems.

Researchers evaluated soil salinity and how it varies across the season and affects rice yields. Results show a consistent pattern of floodwater salinity throughout the season in no-spill systems that did not differ from the pattern in continuous flow-through systems. Floodwater salinity levels are highest early in the season and farthest from the inlet.

Average water salinity levels were low in fields studied in 2014, and no yield reductions due to salinity were observed. However, in 2015 slight yield reductions due to salinity were observed. Further analysis is under way, with the aim of developing a model that can be used to help growers avoid critical, yield-reducing salinity levels.

The pattern of soil solution salinity varied more than the pattern of floodwater salinity, and largely depended on the initial level of salinity in the field. Soil solution salinity was consistently greater in bottom checks. Although further analysis is needed, preliminary results show no relationship between soil salinity and yield.

Variety salinity tolerance

In 2015, a salinity variety trial was conducted in the bottom check of a field receiving moderately saline water. Eight varieties were compared, with four replicates per variety. There were no significant differences among varieties with regard to tolerance to salinity.

In addition to the field trial, a greenhouse study examined whether there were differences among varieties at different water salinity levels. Four varieties (M-202, M-206, M-205, and M-105) were grown under four salinity levels. The treatments were applied as the rice plants neared heading. The number of tillers, panicles, and grains were recorded, along with percent fertility and timing to 50% heading. M-105 had the highest average yield in both the field trial and greenhouse study under moderately saline conditions. The greenhouse study showed that all varieties suffered as water salinity increased. Further analysis of this data may reveal some varietal differences, as well as a better understanding of how salinity impacts yield.