Improving Water Use Efficiency in CA Rice Systems, 2013


Project Leader

Bruce Linquist, UCCE rice Specialist, Dept. of Plant Sciences, UC Davis

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

Richard Snyder, UCCE biometeorology specialist, Dept. of Land, Air and 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, 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. Scientists previously compared drill seeding and wet seeding, the effect of different planting dates, and rice varieties of different duration.

Studies using a degree-day model to predict crop duration, and thus irrigation requirements, lacked information beyond days to heading. Rice varieties also differ in time from heading to maturity. When considering water use and other management practices, information about other critical stages such as panicle initiation and maturity is needed. Rice varieties can also respond differently to day length, an attribute called photoperiod sensitivity.

Research is focused now on developing a crop-development model that can accurately predict days to panicle initiation, heading, and maturity based on planting date. The model will account for both temperature and photoperiod sensitivity. This model will help growers plan management decisions related to water use.

In 2013, researchers monitored panicle initiation, heading, and maturity for eight common rice varieties—M-104, M-202, M-205, M-206, L-206, M-401, CM-101, and S-102—in field plots near each of the statewide variety trials. They were planted between April 29 and May 23. Throughout the season the plots in this study were visited regularly to determine stage of rice growth. As found in previous years, all varieties had similar times to panicle initiation (about 52 days). This was true even for M-401, a late-maturing variety. The real difference between varieties is in the time between panicle initiation and heading and, to a lesser extent, between heading and maturity.

In addition, these rice varieties, as well as M-105, were planted in a temperature-controlled greenhouse to quantify the effect of photoperiod on rice growth and development. Varieties were planted at five different dates two weeks apart between April 17 and June 12. Crop growth stages were closely monitored and recorded for all varieties and planting dates. Days to panicle initiation were very similar for all varieties and planting dates, averaging 37 days. As in the field trial, the real difference among varieties occurred between panicle initiation and heading and from heading to maturity.

Using a degree-day model to account for differences in temperature between the different planting times, three groups have been determined:

   • Photoperiod sensitive—M-401

   • Moderately photoperiod sensitive—CM-101, M-104, M-105, M-202, M-205, M-206

   • Photoperiod nonsensitive—S-102, L-206

The photoperiod nonsensitive varieties required the same amount of degree-days to reach heading regardless of planting time. For all the other varieties the number of degree days required to reach panicle initiation was high for late April/early May planting dates and then decreased. In the moderately sensitive varieties (with the exception of M-105), late planting in June also resulted in a longer period from planting to panicle initiation. For these varieties the shortest time from planting to panicle initiation was with the mid-May plantings.

Based on temperature and photoperiod data from the greenhouse study, a photothermal model for M-202 that predicts days to 50% heading was tested. It predicted time to heading better than a pure degree-day model. The model tested on photoperiod nonsensitive varieties S-102 and L-206 accurately predicted heading.

To help improve the accuracy of this model, air and water temperature were recorded to quantify their effect on degree-day calculations. In a related study, air, water, and within-canopy temperatures were recorded in three different water management systems. (The drill-seeded system often took seven to 10 days longer to mature than water-seeded rice.) Information from these studies will help fine-tune degree-day calculations.

Research results from 2013 are encouraging. The crop-development model accurately predicted days to heading for S-102 and L-206. Progress has also been made in developing a photothermal model. Work in 2014 will focus on completing the photothermal model for all tested varieties and to have the model predict panicle initiation and maturity. The long-range goal is to develop an online application that will allow growers to determine the stage of crop development based on planting date and variety.