Suboptimal Conditions and Preflood Nitrogen

by Jarrod Hardke, Rice Extension Agronomist - May 19, 2024

Scattered rains and amounts over the past few days have thrown a big wrench in some fertilizer and flooding plans. Hello northeast Arkansas and your Saturday morning surprise.

The first thing to remember is we prefer to run a DD50 report (https://DD50.uada.edu) to know where we stand in crop progress.  We want 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 “wasting good money”.

However, given the upcoming forecast that has rain starting Wednesday and extending for days, it may be the situation of “a good plan today is better than a perfect plan tomorrow.”  Meaning that waiting for ideal conditions next week may leave us in the same boat we’re in now, just a week later. Let’s talk scenarios:

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 postflood.

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 similar to 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 preflood 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.

Field is flooded:  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 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.

Call if you have questions or want to talk through scenarios.