There are always many questions that come up every year about starter nitrogen (N) applications in the drill-seeded, delayed flood rice. I thought it would be prudent to answer some of these questions now, so that you can determine if you want to include a starter N application this spring.
The most common question I generally get is, “Will a starter N application result in a yield response at the end of the year?” Previous research on starter N applications in Louisiana and Mississippi has shown that a starter N application of 20 pounds of N per acre will not always result in a grain yield increase at the end of the year.
However, you are more likely to see a starter fertilizer N yield response in a clay soil as compared to silt loam soil. This is most likely due to the ability of clay soils to “fix” or make ammonium-N temporarily unavailable for uptake and the slower diffusion rate of ammonium-N observed in clay soils.
Coincidentally, these are also the same reasons that we often see that we typically need 30 pounds of N per acre more on clay soils as compared to silt loam soils.
Another oft asked question is, “Is there an agronomic advantage to using a starter N application in rice?” The answer here is an emphatic yes.
While you should not expect a yield advantage from a starter N application every year, there are advantages of the application that cannot be denied. One advantage is that it will stimulate faster vegetative growth. This is especially evident in cooler weather when the rice seems to grow very slowly.
Faster early-season growth will lead to a rice stand that is more competitive with weeds and, in turn, will result in a stand that can be flooded a week or so earlier than rice not utilizing a starter fertilizer application.
This is highly beneficial for rice because the flood is our biggest weed control tool that we have in our toolbox. Starter N applications will also stimulate uptake of other plant essential nutrients like phosphorus (P), potassium (K), sulfur (S), and zinc (Zn).
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One of the biggest negatives about starter N applications in rice is the efficiency of the application. Only about 2 pounds of the N from a 20-pound-per-acre application actually makes it into the rice plant prior to the tillering stage of development and flood establishment.
The remaining 18 pounds of the applied N will be in the nitrate-N form by the time the flood is established. The nitrate-N will be turned into a gas and be lost through a natural process called denitrification once the flood is established and the oxygen is depleted from the submerged soil.
This is why you should never count the starter N fertilizer application in your seasonal N target.
I personally like to use starter N applications in rice because of all the positive things they bring to the table, even though they are probably not going to result in a measurable economic advantage at the end of the season. If you do decide to use a starter N application this year, consider the following.
Be sure to incorporate the fertilizer N into the soil quickly with an irrigation event (or rainfall) to get the nutrient to the roots of the plant. This is especially important if you are using urea. If you are using urea and cannot irrigate the N in quickly, consider treating the urea with a urease inhibitor.
Since the application is so inefficient, consider not using more than 21 pounds of N per acre. If you are not incorporating the N into the soil prior to planting, consider applying the N around the 2-leaf stage of development just prior to an irrigation event.