Arkansas Rice: Mid-Season Nitrogen – Soil-Applied or Foliar?

Burn on rice from foliar N application. Photo: University of Arkansas

As has been common this time of year the past few years, there are recommendations being made to apply nitrogen (N) using a foliar spray application piggy-backed with a fungicide instead of applying urea at late boot to hybrid rice.

The reasoning is straightforward – it’s cheaper to add in a foliar N product if you’re already going across the field with a fungicide.  The problem is, there is no evidence to support that a foliar N product can supply the needed amounts of N that a urea application can.

For hybrid rice, we recommend applying 30 lb N/acre (65 lb urea) at late boot (flag leaf collar visible) up to beginning heading.  From midseason and beyond, rice is capable of taking up urea N with high efficiency (70% uptake).  Foliar applications of N products cannot supply these N rate levels.

A foliar N product containing 32% N can only deliver 3.2 lb N per gallon (for a product with a weight of 10 lb/gal).  Even if a foliar is taken up with the same high efficiency as urea, 70% of a 3.2 lb/gal foliar is just 2.2 lb N versus 70% uptake of 30 lb N as urea is 21 lb N.

Again, there are charts being sent around that suggest 1 lb N applied foliarly is equal to 5-10 lb N applied to soil.  This is false – a pound is a pound.

If you attempt to increase the rate of a foliar N product to compete with urea, then you have the issue of it becoming very cost-prohibitive, and the chances of severe foliar burn to rice increase.  Stick with urea for the late boot application on hybrids – years of data show increases in grain yield, head rice, and total rice.  Each of these increases alone is small but put together generate a nice return on investment for the urea application.

 




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