Applying Nitrogen During Wet Weather

Apr 07, 2014

. Nitrogen deficient triticale forage. Notice older leaves are yellow and stems have a purple cast.

Figure 1. Nitrogen deficient triticale forage. Notice older leaves are yellow and stems have a purple cast.

Recent rains have been, in many areas of the Panhandle, “too much of a good thing.” Too much rain can limit farm equipment access to fields, delay scheduled planting, and other management activities, and wash away valuable fertilizer applications. Nitrogen in particular is mobile and volatile in water logged soils. Given the challenges of excessive water, are there ways we can determine, after significant rain events, if soil nitrogen (N) has leached beyond our crop’s root zone?

Fortunately, plants with deep roots can capture soil nitrogen as it leaches (or travels) past surface roots, but you still need a reasonable estimate of how deep those roots are. For example, a well-managed, adequately fertilized, perennial grass pasture, such as Bahiagrass, can have roots exceeding five feet deep. Poorly managed, heavily grazed, or annual grass pastures, however, will have shallow root systems, and are not capable of capturing soil nitrogen, as it quickly leaches past the shallow roots during heavy rain events.

The following are a few considerations that you can use to estimate the depth to which nitrogen (N) fertilizer might travel following a rain event.

First, most of our plant-available soil N is typically in the nitrate form, and nitrate readily moves through the soil with water. Organic, urea, or ammonia N does not readily move through the soil with water, and it takes soil microbes (bacteria) a couple of weeks to convert these forms of N into the plant-available nitrate form.

Second, north Florida soils generally have a water infiltration rate of approximately 1 inch per hour. So, if it rained more than 1 inch per hour, we will likely experience temporary run-off or ponding based upon a soil infiltration rate of 1 inch per hour. Nitrogen can be lost during ponding situations due to de-nitrification (volatilization into the atmosphere.)

Third, north Florida’s surface soils can hold approximately 0.6 to 1.2 inches of water per foot of soil at field capacity (FC = the amount of water held after free drainage, i.e., no longer dripping wet).

So, what are some management actions you can take using these considerations?

Do not fertilize saturated soils. After more than 6 inches of rainfall over a day or two, you may have lost most of your plant available nitrate-N fertilizer, especially if it was applied more than two weeks prior (anhydrous more than 4 weeks prior) to the rain event. Remember that it is the nitrate form that moves with the water and it takes soil microbes a couple of weeks to convert ammonia or urea N to the nitrate form.

You might consider reapplying up to half your N fertilizer if it rained from 3 to 6 inches over a day or two, or if you have field ponding lasting 3 days or more.

Nitrogen replacement is probably not necessary if the rain event was less than 3 inches over a day or two, if the fertilizer was applied within a week of the rain event (anhydrous less than 3 weeks), or if field ponding lasted less than 3 days.

If you have shallow-rooted, heavily grazed plants, however, even smaller (2 to 3 inch) reoccurring rain events can leach nitrogen below your root zone. In these crops, if lower (older) leaves are turning yellow or fading, while younger leaves remain green, your crops may be experiencing nitrogen deficiencies (figure 1).

Source:ufl.edu

Video: Why Your Food Future Could be Trapped in a Seed Morgue

In a world of PowerPoint overload, Rex Bernardo stands out. No bullet points. No charts. No jargon. Just stories and photographs. At this year’s National Association for Plant Breeding conference on the Big Island of Hawaii, he stood before a room of peers — all experts in the science of seeds — and did something radical: he showed them images. He told them stories. And he asked them to remember not what they saw, but how they felt.

Bernardo, recipient of the 2025 Lifetime Achievement Award, has spent his career searching for the genetic treasures tucked inside what plant breeders call exotic germplasm — ancient, often wild genetic lines that hold secrets to resilience, taste, and traits we've forgotten to value.

But Bernardo didn’t always think this way.

“I worked in private industry for nearly a decade,” he recalls. “I remember one breeder saying, ‘We’re making new hybrids, but they’re basically the same genetics.’ That stuck with me. Where is the new diversity going to come from?”

For Bernardo, part of the answer lies in the world’s gene banks — vast vaults of seed samples collected from every corner of the globe. Yet, he says, many of these vaults have quietly become “seed morgues.” “Something goes in, but it never comes out,” he explains. “We need to start treating these collections like living investments, not museums of dead potential.”

That potential — and the barriers to unlocking it — are deeply personal for Bernardo. He’s wrestled with international policies that prevent access to valuable lines (like North Korean corn) and with the slow, painstaking science of transferring useful traits from wild relatives into elite lines that farmers can actually grow. Sometimes it works. Sometimes it doesn’t. But he’s convinced that success starts not in the lab, but in the way we communicate.

“The fact sheet model isn’t cutting it anymore,” he says. “We hand out a paper about a new variety and think that’s enough. But stories? Plants you can see and touch? That’s what stays with people.”

Bernardo practices what he preaches. At the University of Minnesota, he helped launch a student-led breeding program that’s working to adapt leafy African vegetables for the Twin Cities’ African diaspora. The goal? Culturally relevant crops that mature in Minnesota’s shorter growing season — and can be regrown year after year.

“That’s real impact,” he says. “Helping people grow food that’s meaningful to them, not just what's commercially viable.”

He’s also brewed plant breeding into something more relatable — literally. Coffee and beer have become unexpected tools in his mission to make science accessible. His undergraduate course on coffee, for instance, connects the dots between genetics, geography, and culture. “Everyone drinks coffee,” he says. “It’s a conversation starter. It’s a gateway into plant science.”