The overall objective of this project is to quantify the effect of low water temperature on yield loss due to blanking and reduced plant productivity.

Water temperature has increasingly become a matter of concern to California rice farmers because of concerns over regulatory decisions to improve fish habitat quality.  Based on preliminary results from the previous season’s research, agronomists were able to quantify the impact of water temperature in yield loss for two different fields.

In 2001 these two rice fields — one near Thermalito Afterbay and another near Richvale — with cold water inlets from adjacent irrigation district canals were fitted with temperature sensors laid out on a grid.  In 2002 a third field, located west of the others, was added.  Water and canopy temperature were measured.  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 of the field.  In addition, thermal infrared remote sensing was used to record thermal images of the field.

Data from these two fields showed a great deal of variability in water and canopy temperature, and a correspondingly very significant relationship to yield.  Last year’s results essentially confirm the findings from 2001 — that a significant relationship exists between water temperature and yield loss, primarily due to causes other than blanking.

The good agreement between the temperature measured with the sensor and the thermal aerial image provides evidence that early morning temperature distribution — or at least the location of cold areas of the check — can be detected using remote sensing from an aircraft.

Previous studies have shown that cool air temperatures during panicle formation can lead to subsequent blanking and reduced yields.  This project indicates that even in “normal” growing seasons, with no cool air problems, there can be significant yield reductions due to water, rather than air temperature effects.  Farmers will need to quantify and separate the effects in yield due to cool air temperature from the effects of low water temperature to illustrate to water agencies that changes of water delivery mechanism that would substantially reduce water temperature may adversely impact crop productivity. 

A precise quantification of the yield loss due to temperature effects will provide the grower with the capacity to determine whether the economic gains associated with on-farm investments to improve temperature distribution in rice fields are worth the costs.