Arkansas rice crop hitting its stride

Mild weather in Arkansas is over for the foreseeable future, and timed almost perfectly with a new growth stage in the rice crop, it’s time to put out pre-flood Nitrogen and go to flood.

Hot and dry weather should allow growers to push things as fast as they can go. Give it all you’ve got, but be careful in the heat. Herbicides that require moisture to work likely won’t work so well at these temperatures, and herbicides that work better in the heat will get even hotter. Choose carefully and keep in mind that with this week’s forecast heat, flood-up time may take longer than expected making these products more likely to provide a benefit.

The weather remains highly uncooperative as we head into mid-June, and many scenarios are cropping up that throw a wrench into our desired preflood nitrogen (N) management plans. It is best to have N applied by the final N date, but there is time built in after that for getting the field flooded. It can be better to wait a few days after that final N date to get optimal soil and environmental conditions for fertilizing rather than force fertilizer into a bad situation exacerbating loss potential and throwing away input costs.

Field is dry: Minimum expectations – 1) silt loams – shoes leave little to no impression and soils are at “whitecapping”; 2) clays – surface soil is not tacky and starting to crack.Use urea treated with a recommended NBPT product to minimize ammonia volatilization losses which occur when urea is left on the soil surface unincorporated by irrigation or rainfall. Potential N shortfalls can be caught and corrected with no yield penalty 6-8 weeks post flood.

If the field is muddy, wait until the field is mostly free of standing water, and use urea treated with a recommended NBPT. After application, attempt to let the soil dry beneath the urea, if possible, but if rain occurs on the applied urea, flood the field. Letting the soil dry prior to flooding will allow the urea to incorporate into the soil and will perform similarly as if optimal conditions were present at the time of flooding.

When urea is applied to mud and flooding commences before the soil dries the urea does not incorporate into the soil, but rather dissolves into the water and is lost from the floodwater before the plant can take it up. If muddy conditions are present and unlikely to dry before another rain, increase the pre flood rate by 10-20 lb N/acre (20-40 lb urea/acre) and begin flooding. Under very poor conditions, consider a 20-30 lb N/acre (40-60 lb urea/acre) rate increase.

If conditions have created standing water through the final recommended time to apply N, set spills and begin applying N in a “spoon-feed” manner – 100 lb urea/acre once a week for 3-4 weeks. For hybrids, a minimum of 3 and possibly 4 applications of 100 lb/urea/acre are needed to maximize yield.

For most varieties, a minimum of 4 and possibly 5 applications of 100 lb urea/acre are needed to maximize yield. Some varieties may have lower N requirements (such as DG263L) and may fall somewhere in between the hybrid/variety spoon-feed recommendations.

Urea is a great nitrogen (N) fertilizer source, especially for rice, due to its high N analysis and granular form that aids in both ground and aerial application. There is no perfect N fertilizer source and for all the good qualities of urea, ammonia volatilization is its fatal flaw. Urea is technically an “organic” compound as it contains carbon, oxygen, nitrogen, and hydrogen. Urea must be dissolved and then hydrolyzed or converted to ammonium before the plant can take it up. The process of urea hydrolysis (conversion from urea to ammonium) is catalyzed by
an enzyme known as urease – which is basically everywhere.For most soils and environmental conditions, it requires 2-3 days before we see appreciable N loss via ammonia volatilization.

A quality urease inhibitor that contains NBPT is worth its weight in gold when it comes to mitigating ammonia volatilization losses from urea applied preflood. If you are on clay soils or require 3 days or less to flood then you probably will see no benefit from a urease inhibitor. If you are on a silt loam soil and conditions are right, you can lose as much as 30-40% of your applied urea-N in as little as 7 days.

The heat is on in the Arkansas rice crop and with a little knowledge and preparation, growers can smoothly transition their fields to flood.


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