“We know that we need good soil fertility for good crops, but sometimes too much of a good thing can be as bad as not enough,” explained Organic Valley Agronomist Mark Kopecky.
Kopecky was leading a discussion about soil health and the impact of rotational grazing on pastures, during a pasture walk at Aaron Fisher’s Echo-Valley Organic Farm, near Fort Plain, NY.
Soil maps of the 200-acre property were distributed to attendees.
Soils on the property include Lansing soil, a deep, well drained soil; Dunkirk, also very deep, well drained, silty soil; and Mohawk, another deep, well drained soil, with a dark surface layer.
“There are five factors that are responsible for the tens of thousands of different types of soil in the world,” Kopecky remarked. “Plant material, what the soil forms from; topography of the land, whether it’s steep, sloped, whether it’s valley bottom or whether it’s facing north or south; all of these things matter. The type of biological influences — dominant plants and sometimes animals — impact it.”
Climate is the fourth factor impacting soil type, and the 5th factor is time. “How long it’s been in place. In flood plains, every time the river floods and you get a new deposit of soil, that would be considered really young soil.”
Kopecky said soil type remains the same for thousands of years.
“Soil surveys have been done across the United States mapping out every acre across the states. You can go online and find mapped surveys for any property.”
This is recommended before purchasing farmland.
Fisher says although his over 100 head of sheep are no longer there, they originally played a large part in his rotational grazing plan. He showed pastures where he had rotated the sheep with his dairy cattle.
“Six years ago this field was nothing but golden rod. I mean it was completely,” he emphasized. “It wasn’t cut for a couple of years before that. This was almost all tall weeds. The first couple of summers I mowed it and let it lay, because it was nothing but weeds.”
Fisher said he had so much land and no added help, so he was too busy to plow and reseed, but new species developed in response to grazing management.
Fisher said the only thing he added to the field was manure, no added lime.
“We grazed it, made hay off of it and put a lot of manure on it. This field has gone from golden rod and weeds to almost all orchard grass.”
Other fields, using the same method of rotation, also show a diversity of beneficial plant species, annuals and perennials, grasses and legumes including Birdsfoot trefoil, known as a non-bloating legume.
“Careful pasture and soil management are really matter of attention to detail,” Kopecky said. “Knowing when to move livestock in and out of paddocks so they get the highest intake of the excellent quality forage is extremely important — and there is a place for clipping on some pastures that get too rank, especially early in the season. Leaving a good amount of residual forage, at least 3-4 inches, post-grazing, helps the stand to recover faster resulting in more pasture forage for the cows over the season. And soil fertility is extremely important. Providing lime and nutrients to soils that need them really improves the quality and yield of the forage, but it’s also important to avoid excesses.”
Kopecky reminded attendees that phosphorus levels recommended by some consultants may be much higher than university recommendations. “There are still principles we can use to help us sort through how much phosphorus we really need in our soils.”
“Phosphorus levels in soils depend on the ancestry of the soil and how it’s been managed during its farming history.”
Phosphorus availability in soils is strongly associated with pH.
“At low pHs, phosphorus tends to bind up with iron and aluminum in soils and becomes unavailable to plants,” said Kopecky. “At high pHs, phosphorus can bind to calcium and magnesium and that also decreases it’s availability. Acidic soils bind up phosphorus worse than alkaline soils do. Phosphorus is most readily available to plants at pHs of at least 6.5. If the soil pH drops below 6.0, phosphorus becomes very unavailable. Applying lime to very acidic soils is always a good idea, and one of the benefits of that is to help phosphorus become more available even without adding it as a supplement.
If we identify a phosphorus deficiency in soils, there are several things we can do to correct that. The most common sources of phosphorus for organic cropping systems are manure and rock phosphates. For farms that have a livestock or poultry enterprise, the manure these animals produce should be the first place we look when we need to add phosphorus to soils. If we don’t have enough of a supply of manure to meet the phosphorus we need, or if we need only phosphorus and not the potassium that also comes with manure, we can use rock phosphates.”
Kopecky said although manure is a great source of phosphorus, it is often focused on as a nitrogen source for crops, such as corn.
“If we use manure as the only source of nitrogen for growing corn, we will continue to raise phosphorus levels over time because manure provides nutrients at different proportions than what crops need to grow. This can be helpful for soils that are low in phosphorus, but if we already have high phosphorus levels it can eventually cause problems. As phosphorus levels in soils continue to rise to extremely high concentrations, the soil gets to a point where it just can’t hold any more and the phosphorus begins to leach out of the profile and end up in groundwater. This can cause problems in well water, and where groundwater seeps into surface waters, etc.”
High pH and potassium levels can cause problems for forage quality and soil biology.
Soil testing is an important step in evaluating what your pastures actually need, however, as Fisher has discovered, plant testing will provide an even more reliable assessment of what the plants are lacking for quality growth.
Plant testing is now a quick process, with excellent accuracy.
Kopecky agreed that plant tissue analysis is valuable for crop management and may be used to make fertilizer recommendations during the growing season for some crops. In combination with soil testing the information provided is used for troubleshooting and diagnosing nutrient deficiencies to determine fertilizer requirements.
Aggressive grazing in the spring, followed by clipping and summer recovery periods allows the composition of the pastures to change.
“I’m an advocate of clipping pastures, especially when you have a heavy stand of orchard grass like you have here,” Kopecky remarked.
This event was produced by NOFA-NY with support from Organic Valley Cropp Cooperative.