Measuring the Effect of Low
Water Temperature on
Blanking and Grain-01 



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Project Leader and Principal UC Investigators

Richard E Plant, professor, Department of Agronomy and Range Science, UC Davis

Randall “Cass” Mutters, farm advisor, UC Cooperative Extension, Butte County


Previous studies—and grower experience—have shown that cool air temperatures during panicle formation may lead to pollen sterility and hence to blanking and yield reductions. Water temperature has become a matter of concern because of the desire of regulatory agencies to improve habitat quality for fish. A new project was begun to document the effect of low water temperature on blanking and grain yield.

RiceGrain.JPG (25989 bytes)Two rice fields, one near Thermalito Afterbay and the other near Richvale, were used in this study. Cold irrigation water was obtained from adjacent irrigation district canals. Recording temperature probes were placed at strategic points in the fields. Each probe contained two temperature sensors, one in the body of the recording device; the other at the end of a four-foot lead. The body of the sensor was kept at canopy height and the lead was placed in the water.

At each grid point, water and canopy temperature were recorded. As the rice grew, the canopy sensors were moved upward so that they were always near the top of the canopy. Hourly temperatures were recorded from both sensors throughout the growing season. At harvest, yield components and percent blanking were recorded in the vicinity of each sensor. Sensors were removed prior to harvesting and yield maps were created for each field. In addition, infrared remote sensing was used to record thermal images of the field.

Based on preliminary results, researchers were able to precisely quantify the impact of water temperature in yield losses in the two fields. The main effect of low water temperature on yield reduction is delayed crop growth. These effects are even more important during the early growing period, indicating that the cold water temperature significantly delays crop development. Even in a “normal” growing season, with no problem of cool air temperature there can be significant reduction of yield due to water temperature.

Farmers will need to quantify and separate the impact to yield due to cool air temperature from the effects due to low water temperature to illustrate to water agencies that changes in the water delivery practices that would lower water temperature may also adversely affect crop productivity. A precise quantification of the yield loss due to temperature effects will provide growers with the information needed to determine whether the economic gains associated with improving temperature distribution are worth the costs to modify on-farm irrigation systems. For instance, would an investment in warming ponds offset cold water-induced yield reductions?


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