Arkansas Rice: Nitrogen Management, Preparing for Flood/Irrigation

    Photo: ©Debra L Ferguson

    Survey says – 90% planted.  Given the rain events last Saturday and then again Tuesday/Wednesday, we more or less jumped to 100% planted without dropping a seed.  Of course, there will still be some fields planted in June, but the shouting is essentially over.

    Now we move our focus to the serious business of taking rice to flood (or irrigation for row rice).  Any rice that emerged by around the first of May (maybe 40% of acres) is either past the final recommended date for preflood N or is approaching it this coming week.  Conditions look dry with warm, moderate temperatures – a great week to get things done!  A lot of info on nitrogen management included in this week’s update.

    Along with trying to get fertilizer out, there are definitely some weed issues to clean up as fields were needing to be sprayed prior to rain this week but wind wouldn’t allow it.  Use caution on young rice when trying to clean up some of these messes – for burner type herbicides I like to see 2 full leaves on rice before burning it back.  Depending on the mess though, some tough choices will have to be made.

    Let us know if we can help.

    If you still don’t have a copy – download the 2022 Rice Management Guide or pick one up at your local county Extension office.

    NOAA 7 day precipitation forecast

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

    AR Rice Planting Progress 2010-2022

    Fig. 2.  Arkansas Rice Planting Progress, 2010-2022. Click Image to Enlarge

    Flooded Rice Nitrogen Rate Recommendations

    The Nitrogen Rate Calculator (here) is available to help get immediate N rate recommendations for most available cultivars.  The calculator is built to account for N rate adjustments based on cultivar, soil texture (soil type), and previous crop.  These are base recommendations and actual N rate used should be adjusted based on experience and additional tools such as N-STaR soil sampling and GreenSeeker in-season readings.

    General comments on flooded rice N recommendations:

    For hybrids, we emphasize a two-way split using a preflood application and a late boot application.  Some continue to try and move the late boot application up into more of a midseason timing – if you’re doing this and think you’re getting a noticeable response, then I don’t think your preflood N rate is high enough.

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    As with most rice cultivars the preflood N is responsible for most of the yield potential.  Significant yield responses or yield increases >4 weeks post-flood often indicate that the preflood N rates were inadequate or that there was significant N loss leading to low N uptake efficiency.

    For varieties, we’re still trying to move toward more of an optimum single preflood (SPF) approach where we eliminate the midseason N application.  This will allow us to maximize yield while saving on N input via a reduction in the season total N rate.

    To successfully utilize the SPF approach for varieties, we need to treat urea with NBPT, be able to flood timely (around a week’s time), and keep the field flooded/saturated for as close to 3 weeks following the initial flood event as possible.  Using multiple inlet rice irrigation (MIRI; polypipe) can help tremendously with this, in addition to the water and pumping cost savings that go along with using MIRI.

    If an SPF approach does not fit your farm or fields, then using a preflood followed by midseason approach is still good.  Just remember that we’re no longer as concerned about the exact growth stage for the midseason timing – instead, we want to focus on being at least 4 weeks since the preflood N was incorporated AND be past green ring (into reproductive growth).

    The window for successful midseason N application is very wide, the worst we can do is apply midseason too early before all the preflood N has been taken up by the rice plant and not get the full benefit of the midseason N application.

    Screenshot of Rice N Rate Calculator

    Fig. 3.  Screenshot of N Rate Calculator.

    See 2022 Rice Management Guide for more details.

    Furrow-Irrigated Rice Nitrogen Recommendations

    I think most are getting more comfortable with N management in furrow-irrigated rice (FIR; row rice), but now is a good time to review current recommendations.  We do advocate that there are a few strategies available that can help you achieve maximum productivity.

    If you see “preflood” rate mentioned, we mean the rate you would normally apply prior to flood if you were flooding the field.    The recommendations below are also based on rice in soybean rotation.

    Hybrids

    Work from base preflood rate of 120 lb N/acre on silt loams and 150 lb N/acre on clays.  Note that these strategies focus on early-season N management.  We still recommend 30 lb N/acre (65 lb urea/acre) at late boot in addition to the early season N strategies for hybrids described below.

    Silt loam option 1:  starting at the 5-leaf stage, make 3 applications of 46 lb N/acre (100 lb urea/acre) spaced 7-10 days apart.

    • Example: Day 0 – 46 lb N/acre, Day 7 – 46 lb N/acre, Day 14 – 46 lb N/acre

    Silt loam option 2:  Apply half the recommended preflood N rate at the 5-leaf stage, followed by 2 additional applications of one quarter of the preflood N rate spaced 7-10 days apart.

    • Example: Day 0 – 60 lb N/acre, Day 7 – 30 lb N/acre, Day 14 – 30 lb N/acre

    Silt loam option 3:  An excessive preflood N rate (150% of standard) has produced optimal yields, but greater risk involved than split methods.

    Clay soil option 1:  Apply half the recommended preflood N rate at the 5-leaf stage, followed by half 10-14 days later, followed by an additional 46 lb N/acre (100 lb urea/acre) 7 days after the 2nd application.

    • Example: Day 0 – 75 lb N/acre, Day 10-14 – 75 lb N/acre, Day 21 – 46 lb N/acre

    Clay soil option 2:  starting at the 5-leaf stage, make 4 applications of 46 lb N/acre (100 lb urea/acre) spaced 7-10 days apart.

    • Example: Day 0 – 46 lb N/acre, Day 7 – 46 lb N/acre, Day 14 – 46 lb N/acre, Day 21 – 46 lb N/acre

    Varieties

    For pureline varieties, at this time it is recommended to follow the approach of 4 applications of 46 lb N/acre (100 lb urea/acre) spaced 7-10 days apart beginning at the 5-leaf stage.  Some varieties with lower than standard preflood N rate recommendations may be able to perform with only 3 applications but will need to be monitored closely.

    The 4th application (sometimes the 3rd) coincides with the midseason timing so there is not a need for an additional midseason application after your 4 applications are complete.




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