A small farm livestock owner recently asked me about the benefit of pasture aeration and the application of fertilizer and lime. To answer the question, I had to do some review of studies that investigated pasture aeration and fertilization.
That started me thinking about soil quality, pasture condition and the effect that pasture management might have on soil quality.
In general, a question about pasture aeration suggests that there is some concern about soil compaction. In recent years there has been some promotion of mechanical aerators as a treatment for compacted pastures.
There have been a number of studies done to study the effects of mechanical aeration of pastures versus fertilization of pastures. The hypothesis was mechanical aeration would reduce pasture compaction leading to increased pasture production similar to a fertilization response.
The majority of the results have not shown any increase in pasture productivity attributed to mechanical aeration but always showed a pasture production response to fertilization.
Pasture aeration study
In the course of my investigation, I came across an interesting pasture aeration study from Minnesota. This was a multi-year study done on four different farms with aeration treatments repeated for three years on permanent pastures. Soils varied from sandy to heavy clay.
While there was no clear benefit to pasture quantity or quality provided by a treatment of mechanical aeration, there was a soil pH change response to lime application when combined with an aeration treatment on heavy clay soils.
There was a quicker increase in soil pH on aerated and limed pastures as compared to pastures that had lime applied without aeration. This response did not occur on sandy soils, only on the heavy clay soils.
The Minnesota study also demonstrated a quicker response to manure fertilization is measured by increased dry matter production when combined with mechanical aeration as compared to a manure application with no aeration. Again, this effect was observed on heavy clay soils and not on the sandy soils.
It appears that mechanical aeration may have a place in pasture management, but not to relieve compaction. Rather, mechanical aeration may be a tool to help lime and manure applications become incorporated into the soil profile.
This could result in quicker soil pH change and plant response to nutrients.
Of course there are some cautions. First, this was only one study and the positive effect was only demonstrated on heavy clay soils. Second, does the expense of mechanical aeration justify a quicker response to lime and manure application?
This might be an area that needs more research. Possibly a more relevant question for graziers is what can I do with grazing management to build soil quality? Soil quality, in terms of pasture productivity is determined to a great degree by soil structure.
A healthy soil structure combines soil aggregates and soil macropores in a way that favors root growth, soil life, nutrient cycling and storage as well as air and water exchange.
The macro or large pore space in soil is very important because it provides a habitat for soil organisms and provides the openings that plant roots grow into and through.
These are the soils that are loosely packed, and crumbly, usually with good organic matter content.
On the other hand, poor soil structure is exemplified by compacted soils and many of our clay soils. These are soils that are tightly packed, dense, hard to break apart and often with a very low organic matter content.
There are certain biological process and conditions that lead to the development of desirable large soil aggregates and macropores.
– The presence and work of earthworms as they burrow in the soil ingesting soil particles and producing casts.
– The growth of roots and the fungal hyphae associated with roots that develop a sticky network in soil.
– The physical presence of roots, pushing through soil openings and then leaving channels throughout the soil when they die.
– The production of organic glues by soil fungi and soil bacteria.
Organic matter content is another factor that is important in the formation of soil aggregates.
I think that it is obvious that the condition of the pasture and soil quality are interdependent. Further, the condition of the pasture is determined by pasture management.
Focusing on pasture management to improve the quality of the soil is going to be more productive in the long term than looking at an input such as mechanical soil aeration to fix a compaction problem.
Our basic grazing management principles focus on maintaining plant residue (take half/leave half) and providing plant rest.
Attention to these principles will help to build soil organic matter, promote a favorable environment for earthworms and provide a vigorous plant root system.
This is a combination that will create a good soil aggregate and macropore structure.
As you manage your livestock on pasture this fall and winter season recognize that wet soils, dormant plants and heavy stocking densities can combine to decrease soil structure and soil quality, affecting pasture productivity in the longer run.
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