Arkansas Rice: Watching for Post-Flood Potassium Deficiency

    Potassium deficiency in rice. Photo: LSU AgCenter

    Much of the rice in the state has now gone to flood, and the majority of remaining acres will be getting there quickly.  A common issue that we see every year as rice reaches reproductive growth (internode elongation) is potassium (potash) or K deficiency.

    When we fertilize and flood rice the rapid vegetative growth and significant increases in biomass over a relatively short period of time can lead to nutrient imbalances or deficiencies.  The 3-4 weeks after flooding are the time period when K demand is the highest and we are most likely to see deficiency symptoms appear.

    Potassium deficiencies are rarely diagnosed preflood as the plant demand is relatively low.  However, K is required by the rice plant in near equal amounts as nitrogen (N) and is important for many processes associated with water relations, metabolic functions, and the plant’s ability to fight disease.

    Soil testing is the first step in proper K management.  Current K rate recommendations based on soil test K levels are very reliable and can help identify and prevent K deficiencies before they ever occur.

    However, there are some cases where soil tests are not taken, or K was not applied preplant and K deficiencies can present themselves in both subtle and dramatic fashion.  This year, increased fertilizer prices also led to the use of reduced K-fertilizer rates, which can increase the chances of observing a K deficiency.

    Since K is a mobile plant nutrient the deficiency symptoms in rice will appear on the oldest, lower leaves first and will be characterized as marginal leaf chlorosis that moves from the tip of the rice leaf towards the collar.  “Hidden hunger” continues to be a real concern.

    Hidden hunger for potash is essentially a K nutrient deficiency that does reduce yield, but goes undiagnosed due to a lack of obvious nutrient deficiency symptoms or mischaracterization of the deficiency as normal leaf senescence (lower leaf drop) due to lack of sunlight, etc.

    Proper identification of K deficiency requires you to push the plant canopy back and really focus on those lower older leaves much like you would do when scouting for sheath blight.

    In extreme cases (and what we observe in research) is that K deficient rice seems to be shorter and struggling to really take off after preflood or midseason application of N then hidden hunger or K deficiency may be occurring.  The most common timing for K deficiency in rice is immediately after midseason N applications.

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    If K deficiency is identified, 100 lb potash per acre (60 units K2O per acre) is recommended at the first onset of symptoms and yield can be salvaged all the way until the late-boot growth stage.  Timing of K application is critical with earlier identification of the deficiency and application of K to deficient rice leading to higher yield potential.

    One way to identify potential K deficiencies is with a Y-leaf tissue sample – which is the leaf blade of the uppermost collared leaf on the rice plantFifteen to twenty Y-leaves are required to have enough sample to complete the analysis and should be collected from the entire field or area of interest.

    Recent research on using Y-leaf tissue potassium concentration indicates that >1.6% tissue K is optimal from green ring through mid-boot.  Our goal should be to keep the Y-leaf tissue K concentrations above 1.6% during this timeframe.

    If you are concerned about K deficiency, a tissue test may help identify potential hidden hunger.  Please remember that there is a wide window of opportunity for successful application of K from preplant to late-boot, but the earlier a potential K deficiency is identified the larger the return on investment.

     




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