Tuesday, December 14, 2010

Circles for Rice Update | by Jake LaRue and Kelly Downing

Currently, the Valley Circles for Rice team is observing fields under center pivots in Brazil, Chile, Zambia, and Australia. Growth stages vary from 1-2 leaf to early tillering.

  • Weed control is a challenge and becomes a big problem if the weeds are not controlled when they are small. Grasses in particular seem to be a problem and, in some cases, are taller than the rice.
    • A plan and knowing available herbicide options when you start a rice crop is critical for pre-emergence and post-emergence treatment.
    • Please follow the herbicide label. If the herbicide is not labeled for rice use, DO NOT use it.
  • Irrigation management requires an understanding of the rice root zone from week to week. When talking "field capacity," we mean that when the soil is completely saturated and a rain event occurs, the rain would either run off the field or leach quickly through the root zone.  Due to this, in general, you should refill the root zone of the crop to within 15% or so of field capacity to allow room for a rain event.
  • An example - rice at early tillering:
    • Root zone -- 7.5 to 10 cm
    • Soil -- silt loam
    • Allow 30% depletion at this stage -- up to 60 mm
    • Crop water use
      • Confirm the evapotranspiration (ET) -- let's assume it is 7 mm/day
      • Assume rice at this stage has a crop coefficient of .35 mm
      • Daily use would be about ET x crop coefficient (7 x .35 = 2.45 mm)
    • Center pivot can apply 9.5 mm/day
    • Probably need to be applying about 6 to 7 mm every other day
    • If you have soils that tend to crack, start irrigation during the tillering stage when cracks are 2 to 3 mm wide
    • Both light, frequent applications and heavy applications can be a problem. Watch your wheel tracks and watch for runoff
    • Check the crop root zone and confirm that you are refilling the profile without runoff or irrigation moving out of the root zone
Remember: the data from soil moisture sensors is only as good as the installation. Make sure your sensors are properly installed and calibrated, and use the "smell test", i.e. if something smells bad (if the readings seem bad), it probably is. Check conditions around the sensors periodically to make sure that what they report is the real situation in the field.

Have questions?  Please enter them into the Comment box below!


  1. Hi Jake. I live in Northern California and understand that flood irrigation is the primary method of growing rice up here. Were not in a drought right now, so getting district water for flood irrigation is ideal especially at the low price per acre ft.. I really like the idea of being more conservative when it comes to water no matter how plentiful it is. So my question is...Say I installed a center pivot on my rice check. How do I get rid of the plant after the rice has been harvested if I cant burn or flood anymore?

  2. Thank you for your comment and it is a good question.

    Each farm operation will manage the rice straw and stubble differently. We do not have any specific experience that we can yet reference in California. In other traditionally flooded areas, we have seen rolling the straw followed by doing typical tillage practices, which similar to what is done where burning is not an option.