by Sally Colby
Dr. Doug Beegle, retired professor of agronomy, Penn State University, wants producers to view forage fertility as a long term investment, different from an annual crop that’s planted and harvested once.
“When we think about forage fertility management, we have to start long before we even put any forage seed in the ground,” said Beegle. “Think about other crops in rotation, what we’re doing in that part of the rotation and the pre-establishment period.”
Beegle says if the producer does nothing else, timely soil tests are the best management move. “Once you’ve made the investment in seed, it’s hard to correct fertility,” he said. “You want the soil test to look good ahead of time.” Beegle added that lime won’t correct pH overnight so it’s important to plan liming at least a year or more ahead of crop establishment.
Even the highest quality lime takes time to ‘help’ the soil. When a lot of lime is required, it’s good to split the applications. Beegle cautions no-till growers to not allow the pH to get to the point where a lot of lime is needed. “In a tillage system, plow some down and apply the rest to the surface,” he said. “That way you get the correct pH throughout the plow layer. On no-till, if you have really low pH and really low phosphorus levels, you should probably till once in a while. Get lime on, get it mixed in and get the pH up where it belongs. Then you can maintain levels by putting lime on the surface.” If pH is low at seeding time, one option is to purchase a finer lime that will react faster.
“Most plants are called luxury consumers of potassium,” said Beegle. “That means they’ll take up whatever is there. So if there’s extra, they’ll take it up. We can end up with forages with really high potassium levels, which can create animal health problems. High potassium forages fed to dry cows dramatically increases the incidence of milk fever at freshening. Some farmers intentionally don’t put manure on certain fields so they know they’ll have some low-potassium forage for dry cows.”
In a normal crop rotation, this excess isn’t a problem. If the farmer is growing corn and hay, manure is applied to corn to get the most economic value from manure nutrients. That builds soil test levels, and hopefully the levels aren’t excessively high after three years or whatever the rotation is. If the crop rotation is into hay, manure isn’t applied and levels go back down. When the crop is corn again, levels build up again, and over time, when manure is applied to corn and not forages, a balance is maintained.
With legumes, Beegle reminds farmers of the importance of inoculation for good nitrogen (N) nutrition to avoid having to purchase N fertilizer. Again, pH is critical and has an effect on the rhizobia that fix the nitrogen. “It’s a good idea to limit N,” he said. “The rhizobia will infect the roots, resulting in nodules that fix nitrogen. If you have too much N, that effect is reduced. When applying N to mixed legume stands, weeds and grass can have an advantage over the legume.” For grasses, N supplementation is necessary, and Beegle recommends 50 pounds of N per ton of expected yield.
Beegle cautions no-till farmers to not allow a situation that requires a heavy application at one time. “One thing to pay attention to, particularly for surface application, is salts,” he said. “If you put too much on, particularly potash, it creates a lot of salt, and a salty soil draws moisture. Instead of the seed taking in moisture and germinating, it will desiccate the seed and affect germination.”
For maintenance after establishing a legume, avoid adding nitrogen. “Adding nitrogen tends to increase competition,” said Beegle. “Adding nitrogen to a legume like alfalfa or clover doesn’t negatively impact the plant, but it can give the other plants in the mixture a competitive advantage.”
Beegle says farmers can use that competition to their advantage. If they’re growing alfalfa/grass mixes for hay, they apply manure to fields that are growing more grass to intentionally push the grass and squeeze out the alfalfa. “They can get a year or two of decent grass hay with a little bit of legume,” he said. “It gets them that grass hay simply because they’ve added nitrogen to give the grass a competitive advantage.”
Farm manure is often an important component of a fertilization program, but manure nutrients don’t usually match up well with crop requirements, and imbalances are often created when manure is used to meet crop needs.
“Manure is a package deal,” said Beegle. “Farmers often use manure to get nitrogen to the crop, whether it’s corn or grass hay or whatever. That tends to put on a lot of excess P and excess K.” Phosphorus is an environmental concern, but potash has serious implications for forage quality and animal health.
Manure is most valuable to grass stands because they typically need nitrogen. Beegle says the standard recommendation is 50 pounds per ton, preferably applied in split applications based on next growth. “For a cool-season grass that has a lot of spring growth and not a lot in summer then more in fall, nitrogen should be applied at greenup,” said Beegle. “Then after harvest, add a little for summer, and more after the next cutting. You’re spoon-feeding it for the next growth to get the most efficient growth on grass.”
While manure is a good source of nutrients, it’s highly variable. Beegle says for farmers who count on manure to meet crops needs, it’s best to have it analyzed. “Also, with manure the nutrients aren’t available, particularly nitrogen, so account for that,” he said. “The big thing is volatilization. The nitrogen in manure is like the nitrogen in urea fertilizer. Depending on how long it’s on the surface will determine availability.” If manure is rained on the same day it’s applied, half the nitrogen might be lost.
Another issue to consider is that in a forage system with grass hay, hay fields are an excellent place to spread manure in fall and winter. “The ground cover will protect the soil from runoff, there’s a crop that will green up and start taking up nitrogen early in the season,” said Beegle. “Put that same manure on a cornfield and it’ll lay there for 6 or 8 weeks before the corn crop takes it up. That’s the wettest time of year and the worst time to lose nitrogen. If you have a choice, grass hay fields are the best place to spread manure in the winter.”
The bottom line is that if you’ve done a good job prior to establishment, a lot of fertilizer at one time isn’t necessary. “That should be your goal,” said Beegle. “To not have to do a lot of fertility management.”