We’ve been dealing with cool, wet conditions combined with herbicide injury and seedling disease issues, and this week we’ve added high winds causing rapid drying. Rice appearance is overall poor at this point, to say the least, particularly earlier planted fields.
In these situations, it’s not uncommon for ammonium sulfate (AMS) or diammonium phosphate (DAP) applications to be made as ‘starter’ applications to get the rice growing. Unfortunately, there is not much basis for these applications, and they carry significant costs.
Do not apply any starter fertilizer prior to the full 2-leaf stage. Rice is still mostly living off the seed until this time and won’t be taking up much prior to this stage.
Do not expect a yield response from a starter application made at the 2-3 leaf stage. The seedling won’t take enough up to significantly contribute to yield. The small root system will not take anything up efficiently.
On silt loam soils the growth response from starter fertilizers has been minimal. You are unlikely to get more than a ‘green-up’ from the application. It might make you feel better but will cost $25-30 out of your budget (that could be used on something like additional residual herbicides).
There has been some documented yield response on silt loam soils, but it was at later growth stages (3-4 or 4-5 leaf) when we could potentially be pushing fields to flood anyway.
On clay soils you can expect a positive growth response from starter N fertilizers. A direct yield benefit can happen at times, and the time to flood can be reduced, possibly saving a herbicide application and allowing for earlier harvest.
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Occasionally there may be times when it’s advisable to apply a starter when the crop is not doing well. However, if conditions are cool and the rice is generally not growing, the N uptake and growth response will be further reduced. Most often, a flush and better growing conditions are what give us the best crop response, not the starter. We can all agree we don’t need a flush right now, but more sunshine and warmer temperatures.
Don’t use the sulfur (S) as justification for the starter application, most soils on which we grow rice contain plenty of S. Response from AMS is from the N, not the S. The only exception are fields with known S deficient areas (sandy fields or those with sand veins) which may need S early and blended with preflood N.
If you do apply starter N, do not count the N units toward your preflood N. Just act like they aren’t there. The rice plant will only take up, at best, 5-10 units of N from a starter application but it can be all over the board. Use your normal preflood N rate.