By Jarrod Hardke, Rice Extension Agronomist, and Trent Roberts, Extension Soil Fertility
With so much rice planted early and much of it emerging, the questions turn to “starter” nitrogen (N) fertilizers. Most often we’re talking about ammonium sulfate (AMS), but sometimes it’s diammonium phosphate (DAP), or a blend of those with urea. For simplicity we’ll focus on AMS but comments will apply to other starter options as well. Here are some general guidelines for using a starter in rice production.
- Do not apply starter N fertilizers at planting. There will be no N left as it takes weeks before seedling rice will take up anything from the soil. Any N applied at this time can be considered a waste UNLESS it is in the form of poultry litter.
- If applying a starter do not apply before the 2-3 leaf stage. Period. Same as above, the seedling won’t be able to take it up yet.
- Do not expect a yield response from a starter application made at the 2-3 leaf stage. If there is any form of yield response at all it will be minimal and not enough to cover the cost of the fertilizer and application ($20 or 4.4 bu at $4.50 rice).
- On clay soils you can expect a positive growth response from starter N fertilizers. A direct benefit to yield is still not expected, but the time to flood can be greatly reduced, possibly saving a herbicide application and allowing for earlier harvest – a huge plus on clayey soils. In most cases, if everything is going very well under warm conditions with ample growth and good soil moisture you should keep your money.
- On silt loam soils the growth response is much less pronounced and so is the overall crop speed up. Generally speaking you don’t get much more than a “green-up” from a starter application on loamy soils. If you think rice on a loamy soil would benefit from a starter fertilizer application, it probably really just needs the flush you’re going to give it when incorporating the starter N.
- There are times when it could be advisable to use a starter on a loamy soil. When rice is truly not doing well – conditions are cold or there is some added stress such as seedling disease becoming an issue – then we may need to force the crop forward.
- Most production fields that have rice in the rotation and are on loamy or clayey textured soils will not respond to sulfur (S) fertilization. Sulfur availability in the soil is directly related to soil organic matter and soil temperature; and most rice soils will have plenty of organic matter to supply season-long S needs for rice. Coarse-textured soils can respond to S fertilization, however these soils are less than ideal for rice production and many other factors will need to be considered. Long story short – most rice produced on loamy and clayey soils will not respond to S fertilization, which is one less reason to apply AMS at the 2-3 lf stage.
Final note: if you do use a starter at the 2-3 lf stage it’s best to not count any of the N toward the preflood N. It’s possible that 5-10 units of N count toward your preflood N rate, but that number can be highly variable depending on management from fertilizer application to flooding. So just act like you didn’t get anything from it to ensure that you maximize yield potential.
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