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    Arkansas Rice: Lack of Rain Will Bring Some Tough Choices

    Rice field. Photo: Horizon Ag

    Well it appears the time for the 4th of July rain is passing without event.  It looks as though we’re in for real problems for the remainder of the summer.

    Without any relief in the next couple of weeks, some very tough choices will have to be made.  Water availability and how far we can stretch things is starting to reach a very problematic point.

    Rice usually gets first priority, but it may turn to a “can we just keep it wet” situation as we try to divert water to corn and soybean to keep them alive and productive.  Ultimately something will have to give, or go without irrigation, if a rain doesn’t turn up soon.

    If there’s any upside to the short-term extended forecast, it’s that it appears we will see a slight reduction in daytime highs and more importantly nighttime temps as rice moves into flowering and grain fill stages.

    Highs above 100 are a point of serious concern for flowering rice.  Nighttime temps remaining at or above 75 are a serious issue for flowering and grain fill.  As long as we can continue to periodically drop below these levels and avoid prolonged stretches, rice can manage.  However, 5 or more consecutive nights of these conditions can really punish us.

    You don’t even want to know what some of the long-term models are currently throwing out there.  I regret having looked.

    I had sincere hopes that I would have something good to say this week, but I’ll have to continue waiting.

    Let us know if we can help.

    NOAA 7-day precipitation forecast

    Fig. 1.  NOAA 7-day precipitation forecast. Click Image to Enlarge

    Boot Nitrogen in Hybrid Rice

    Unlike for varieties, we do not recommend a true midseason nitrogen (N) application for hybrid rice.  We recommend a preflood N application dependent on soil texture (generally 120 lb N/acre on loam soils and 150 lb N/acre on clay soils) followed by a late boot application of 30 lb N/acre.

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    What is late boot timing? Once the flag leaves on main stem tillers are fully emerged to where you can see the leaf collar, up until boot-split / first heads emerging.

    Why the late boot and not a midseason application?  The preflood N rate for hybrids is sufficient to supply season-long N needs for hybrids.  Any potential shortfalls during the season can be resolved by the hybrids taking up additional native soil N to bridge the gap.  So a true midseason is not needed to drive overall yield potential.

    The late boot N application to hybrids serve to reduce lodging potential, slightly improve yields, and slightly improve milling yields.  If you were to make this application earlier at a true midseason timing (i.e. ½-inch internode elongation), I would still expect similar benefits, but some negative consequences could occur such as increased plant height and increased rank (excessive) growth.

    Stick with the late boot timing to get the positives while minimizing the negatives.  I continue to hear of folks pushing the application earlier into midseason, and I can only wonder if that’s a historical idea that “rice needs a midseason N app” but it isn’t based on any research data from the past 10-15 years of growing hybrids.

    Table 1.  Net Return from late boot nitrogen applications to hybrid rice ($850/ton urea).

     

    Stuttgart

    Pine Tree

    Keiser

    MEAN

    No Boot N $309 $272 $354 $297
    30 lb N Boot $349 $279 $400 $326

    The late boot N recommendation is to be applied as urea.  There continue to be pushes for “piggy-backing” a liquid foliar N product with a fungicide at the late boot timing instead of applying N as urea.  The reasoning is always that it’s cheaper to add in a foliar N product with a trip you’re already making.  There is no evidence that a foliar N product can supply the needed amounts of N that urea application can.

    After rice enters reproductive growth, it is capable of taking up urea N with high efficiency (90% uptake) when grown under a continuous flood.  Foliar N applications cannot supply these N rate levels.  A foliar N product containing 32% N can only deliver 3.2 lb N per gallon.  Even if applied at 3 gallons per acre and similar efficiency to urea, you’re only getting 8.6 lb N versus 27 lb N from urea.

    Charts continue to be sent around suggesting that 1 lb N applied foliarly is equal to 5-10 lb N applied to soil.  This is false – a pound is a pound.

    Additional issues are that the more you try to increase that foliar N rate, the greater likelihood of crop burn from the liquid N which can be detrimental late in the season especially if the flag leaf is severely burned.  Running that many gallons of liquid N also puts you in the neighborhood of the cost of urea that is giving you many more units of N.




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