Alfalfa and potassium fertilization: What you need to know

Aug 02, 2019

By Craig Sheaffer, Jake Junger.et.al

Forage crops such as alfalfa remove large quantities of potassium (K) on an annual basis. When manure application is not an option, fertilizer must be purchased to supply K to alfalfa. Potassium can impact plant health, potentially affecting the ability of alfalfa to overwinter. Under-application of K can result in less tons produced per acre. While K fertilizer has historically been cheap compared to the other major macronutrients, supplying removal rates of K to alfalfa annually can result in a significant expense to alfalfa producers.

Research funded by AFREC evaluated forage yield and quality at three locations across Minnesota with diverse climate and soil fertility. Alfalfa stands were harvested for four years beginning in the seeding year.

What does the research say?

Eight modern alfalfa varieties that differed in fall dormancy reaction and high levels of disease resistance had a similar yield and forage quality response to potassium fertilization.

The effect of K fertilization on forage yield varied by location and stand age. Predictably, based on current Minnesota soil test recommendations, the greatest response occurred on soil with initial STK of 35 ppm. There was no response where the initial soil test was 160 ppm.

Forage yields were greatest for 1- and 2-year-old stands and decreased dramatically in 3- and 4-year-old stands. There was no response to K fertilization in 4-year-old stands, and, over all locations, K fertilization did not increase stand or stem density.

Below-ground crown and root mass were increased by K fertilization. Potassium fertilizer reduced forage nutritive value. Reductions in forage crude protein and digestibility are related to decreased leafiness and decreased maturity as forage yield increased.

Application of high rates of K fertilizer to achieve maximum yields will result in luxury consumption of potassium and accumulation in the herbage and roots. High levels of forage K due to luxury consumption may induce parturient hypocalcemia, or “milk fever,” in cows.

Diminishing economic returns on K fertilizer investment are likely if K fertilizer is applied at high rates relative to recommended levels. Despite an increase in K uptake with K fertilization, a net increase in STK was observed after accounting for K removal during harvest, which could be related to the release of K from soil minerals.

What do producers need to know?

Potassium fertilization is important for high forage yields when applied at recommended levels based on soil testing and University of Minnesota guidelines. However, it will not prolong alfalfa stand life or sustain forage productivity as stands age beyond the third production year.

There is no economic or biological advantage for applying fertilizer at rates above those recommended by the University of Minnesota guidelines to achieve high alfalfa yields. Potassium fertilizers should not be applied at levels above those recommended with a goal of accumulating K in the soil.

Potassium fertilization will not increase forage nutritive value but can lead to luxury consumption and K accumulations above those suitable for dry cows.

Intensively harvested alfalfa varieties do differ in forage yield but do not differ in forage yield response to K fertilization. Therefore, producers should select varieties that yield and persist well under their harvest systems and management regimes.

Source : umn.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.”