Fertilizer prices are still high, and in some cases, increasing. During this pinch, cattle producers can make the most of manure to maintain fertility.
“We had a drastic increase for all fertilizers throughout 2021 and into 2022,” said Dr. Amanda Grev, University of Maryland Extension specialist, Forages and Pasture Management. “They’ve started to level out a bit, but overall, prices remain higher than a couple of years ago.”
Despite the increase in fertilizer costs, adequate soil fertility is still essential for forage systems. Adequate fertility is required for good forage establishment, good root growth, nutrient uptake, yield, minimizing weed pressure, maintaining stand vigor over time and providing resistance to drought or disease.
Soil mineralization, fertilizer, manure, other feed or minerals and nitrogen fixation by legumes all contribute nutrients to the system. Routine forage harvest as well as livestock consuming forage result in forage nutrient loss.
Grev offered insight on maintaining good soil nutrition without using fertilizer. “The problem with the cycle is when inputs and outputs are off-balance and the system starts to get off balance,” she said. “We know harvesting and grazing both remove nutrients from a system, but in general, when outputs start to outweigh inputs, we’re mining the soil for nutrients. While we can do this for a short time and not see a huge impact, over time, we see decreased productivity and decreased resistance of the stand.”
In a hay production system, or when forages are harvested, a large percentage of nutrients in forages are removed – up to 80%. With grazing, there’s more cycling, so removal is less.
“A large portion of what goes into animals as they graze is also coming out the other end and is deposited back onto fields,” said Grev. “There’s more cycling naturally than in harvested forage systems.”
She provided an example to illustrate nutrient removal in hay versus grazing: “If we harvest a three-ton crop of hay from one acre, we’re removing, on average, 150 pounds of nitrogen, 22 pounds of phosphorus and 155 pounds of potassium,” she said. “If the same field would be grazed, we would only be removing 16 pounds of nitrogen, 5 pounds of phosphorus and 1 pound of potassium.”
Highly productive fields with greater yields result in higher nutrient removal, which means more nutrients should be replaced to sustain the yield.
In order to replace nutrients with manure, farmers must first know what’s present in soil. A good soil test, including soil pH, is essential. “Soil pH affects utilization of minerals,” said Grev. “As pH changes, even if a nutrient is present in soil, whether or not it’s available to the plant changes based on different pH levels. In more acidic conditions, calcium, phosphorus and magnesium are still present but are less available for plants to uptake. Other nutrients such as copper, aluminum and iron tend to become more available under acidic conditions, and also have the potential for toxic levels.”
For most forage crops, the ideal pH range is between 6 and 7.
As nutrient availability decreases, uptake and availability efficiency decreases. Grev advised keeping an eye on soil tests and applying lime as needed to provide proper nutrient availability. Soil pH affects nutrient availability and influences root growth and development. Roots under more acidic conditions are stunted and unable to extract nutrients and water from the soil.
Manure is a good source of various nutrients. “Manure can supply nitrogen, phosphorus, potassium, sulfur, calcium, magnesium and other micronutrients,” said Grev. “Those are all essential nutrients for plants. We can measure nutrient content of manure; poultry litter contains, on average, the highest concentration of nutrients.”
Manure nutrient availability also varies by whether it’s applied as a liquid or a solid.
“When we go from liquid to solid manure, there’s a big decrease in ammonium,” said Grev. “This is important because ammonium is one of the most volatile components of nutrients. It’s more prone to losses, particularly when liquid manure is applied.”
Solid manure may contain less ammonium but the nutrients are generally more stable and less prone to volatilization.
Manure nutrients can be used to offset fertilizer expenses. “Solid cattle manure spread on a field is usually applied in large quantities, often 10 tons per acre,” said Grev. “With average values, if we apply solid manure at 10 pounds per acre, we’re applying 154 pounds of N per acre, 84 pounds of P205 per acre, and 180 pounds of K20 per acre.”
Current work in Maryland is studying ammonium volatilization on farms applying manure. Each farm applied manure via broadcast and injection. “They measured volatilization, or loss of ammonium, from manure,” said Grev. “For every farm, there was a large reduction in volatilization when manure was injected.”
She said that while injection isn’t always an option for manure, it’s beneficial for minimizing losses through volatilization and also minimizes runoff.
Temperature at application can make a difference in nutrient uptake. “Apply nutrients when the temperature is lower,” said Grev. “As soil temperature increases, there’s an increase in nitrification. If we apply manure in lower temperatures, we’ll see less loss and can maintain more nutrients in manure.”
Nutrient variability in a grazing system varies because animals distribute manure rather than uniform machine application. “Grazing management plays a big role in how nutrients are distributed,” said Grev. “Animals on pasture represent a dollar value, and the manure from those animals also has a value that can be applied to the pasture and can be turned around to produce more forage.”
Dark spots in a pasture usually represent urine or feces deposits and result in a flush of forage growth. “In livestock operations, we see a lot of congregating,” said Grev. “Animals congregate under shade trees, around waterers, near a gate. The animals are grazing throughout the field, consuming nutrients then redepositing nutrients in one spot to create ‘hot spots’ of manure in those areas.”
Grazing management with different rotation configurations can manage the animal application challenge. In a continuous grazing system where animals are not moved, it can take 27 years to get one manure pile per square yard of pasture. “That’s because animals are congregating and returning to their favorite places over and over versus more even distribution,” Grev said. “Moving animals around to different areas of the field helps promote a more even distribution of manure and manure nutrients throughout the field.”
Hay is also a nutrient source, and if a large bale feeder placed in a field can be moved to different areas, nutrients are more evenly distributed in a grazing area.
by Sally Colby