Managing for Nutrient and Soil Retention in Pastured Lands
Posted: April 5, 2017
An early March drive on some highways in West Virginia and Virginia reminded me of some good management methods. In the rolling cattle pastures of that region it is common to spot long strips of hay residue scattered across the pastured slopes from bale grazing. Producers know that rotating feeding locations also rotates animal traffic. The practice comes with a number of environmental benefits including:
- Avoidance of Animal Concentration Areas (ACAs).
- Distribution of manure nutrients across the landscape.
- Widespread hay residual helps to prevent erosion, provide nutrient retention, and returns organic material to the soil.
- Hay residue is less likely to choke out spring re-growth.
- Seeds baled in the hay can help to reseed and improve existing forage stands.
Carbon and Nitrogen Use
In the theoretic world of nitrogen cycling, the carbon in the residual (waste) hay would exist at a high enough level to temporarily tie up the nitrogen from the urine and feces deposited on these areas. This process is largely microbially driven. I like to compare the microbial use of carbon (C) and nitrogen (N) to framing a house. When you construct the frame you need a lot more wood than nails, but you do need both to make a good structure. For the microbe analogy, they also need a lot of carbon (wood) and a smaller proportion of nitrogen (nails) to construct their own bodies. The decomposing hay provides these microbes plenty of C and they tend to quickly grab up N that becomes available. So, imagine microbial carpenters that have lots of wood in a world where nails are scarce. Every time a nail becomes available it is more likely to be grabbed by a carpenter. Turning this back to nitrogen cycling means that the waste hay decomposition is going to help hold N in the pasture, where we want to keep it. The technical term for this is Nitrogen Immobilization. Often C sources can be said to ‘tie up’ N. Immobilization means that the N is not leaving the pasture via volatilization, runoff, or leaching-it is staying where you placed it (via your animal management).
Some may ask, “If this nitrogen is ‘tied up’ then what good is it for my pasture?” This is where natural soil processes come into play. The addition of Organic Matter to your soil helps to hold moisture, build soil structure, and even helps with hoof compaction the next time hay is rotated to this area. The Soil Organic Matter is an area of constant microbial activity, which brings us back to our microbial carpenters. If you’ve ever framed a house, you know that as you work you sweep up piles of sawdust, throw away scrap wood, and bend a few nails. Microbial use of C works similarly, with the simplest loss being carbon dioxide gas from microbial respiration. Imagine microbes cutting up enough wood that they now throw away an occasional nail. In the soil food web, nitrogen becomes available from this microbial activity. In the pasture, decomposition of hay and manure provides plant-available nitrogen. Since microbial activity is largely dependent on temperatures and moisture, nature does a decent job of timing microbial-supplied nitrogen closely with plant uptake in this system.
Evaluate on Rainy Day
March and April are the times when pastures can look their worst; evaluating impacts now allows you to reflect on how you did. It is also a great time to plan for improvement implementation. View your lands with a critical eye and develop an honest evaluation of impact now. For the best read on your impact, look things over analytically on a rainy day.
The largest agricultural contributions to water impairment in our region are the nutrients nitrogen and phosphorus (P), as well as sediment. Every producer and landowner has a responsibility to contain manure nutrients and soil on their lands. In manure and fertilizer management we discuss “nutrient placement,” meaning we land-apply manure where we want it and in a manner that holds it where we place it. Consideration must be given to ground cover, time of year, slope, application rate, impending weather, and distance to the field edge or surface water.
The principles of manure and fertilizer placement should also apply to pastures. Don’t let manure N and P escape when the plants in your pasture can use them. When you set out to improve management practices you might want to consider adopting a mindset that includes ideals like these:
- Nutrients and soil are valuable and I need to keep them to myself.
- Allowing nutrients and soil to escape my management is wrong. It’s pollution. It’s bad for the environment. It’s my responsibility to limit loss.
- My neighbors and the public are watching. A bit of paranoia can be a good thing. Everyone wants to be respected within his or her community.
- Small losses add up, so I need to do my part.
- I understand my land better than anyone, and when I’m honest I know what the problems are. I will take routine planned sequenced steps to improve my environmental loss as time and resources allow.
Now that you’ve looked back to evaluate the current state and impact of your pastures, you can look ahead. Are soil or manure washing off of your land? If so, a management change may help. Animal Concentration Areas are going to exist, so explore opportunities to change your outdoor systems to encourage animal congregation in environmentally safe locations. Look upslope (or “upstream”) to evaluate if there are ways to redirect oncoming water. Sometimes additional fencing is a simple solution to segregate acceptable sacrifice areas from areas where pasture quality can be improved.
Looking ahead also means continued evaluation. Through the coming growing season, you may find areas that didn’t look good at the end of winter may not be providing quality pasture comparable to other areas. If changes are made, continue evaluation and tweaking management as you aim for an ever-higher bar. Changes in grazing management can lead to decreased impact of ACAs and use of animal behavior to get the animals to place their nutrients where you want them. That is just like the principles of manure application to cropland, and just like the bale grazing practices I saw on my recent drive.
About the Author:
Robb Meinen is a Senior Extension Associate in the Department of Animal Science at Penn State University. His main duty is to coordinate education for the PA Commercial Manure Hauler and Broker Certification Program.