Soil Samples and Tests

[dominiquer60]

The discussions on sub soiling have spurred further thoughts on soil sampling and testing.

In the Keyline plow thread (http://www.draftanimalpower.com/showthread.php?2740-Keyline-Plow/page3&highlight=subsoil) I made a reference to a soil test for microbial activity and “health” in post #16 that the Nordells had tried at some point.

I believe that Tim addressed this issue in a later post: “Soil respiration is a measure of microbial activity but in our work we have not pursued it as the best measure of a balanced and active soil. The reason is it can be manipulated fairly easily by tillage, moisture, etc. so a measure of respiration is more like a snapshot than a reliable indicator of a longer-term stable and sustainable state. Our approach is to incorporate practical and effective management options, manure, cover crops, low-disturbance tillage of the topsoil, permanent vegetative cover with botanical diversity where practical,etc. We know these things will improve soil quality. And, our goal is not to maximize microbial communities but to produce sustainable yields of grass and pasture. So that tends to be the focus of our measurements and assessment.”

A couple weeks ago I went to a Soil Pathogens Workshop put on by Cornell Cooperative Extension. It was the kind of workshop that makes you wonder how we can grow anything to eat at all, but they gave out a lot of good information. It was the first educational opportunity put on by Cornell where chemicals were not the answer, this was very refreshing. They really stressed cover crops and rotation and once in a while mentioned a chemical treatment but only because they exist and not because they where the most effective means of treatment. Anyway they were really pushing their new soil health test that can be found here http://soilhealth.cals.cornell.edu/.

If you go to this page and click on “soil health testing services for 2012, and how to prepare and ship samples,” then scroll down to Results and Interpretations #3 and click “Standard Cornell soil health assessment:” they have a detailed pdf about taking the soil samples and the soil health tests that are done. They only do these tests between March 15th and July 15th due to “due to seasonal variability in biological and physical indicators.”

I understand that this test is a snapshot like Tim states, however is there an ideal time of the spring, soil moisture or tillage condition that one should take into consideration when taking samples for a test like this?

I ask this because I may be able to use a field next year and I have little knowledge of this soil and would like some way to assess what I have going on there. The past farmers have used it for conventional corn for years and know it needs lime and is compacted, it is a sandy loam soil. I know it can take years of observation to really know a soil well, but jumping in feet first it would be nice to have a snapshot. I generally use Brookside Lab for soil testing and like the format of the results (or at least they are what I am used to), would a test like this really provide me with a better sense of what I am getting into?

I just bought a soil probe and they gave out nice trowels at the soil pathogen workshop so I am going to do some investigation soon and see what I can find just by looking first.

[Tim Harrigan]

It is not really easy to evaluate soil profiles for compaction unless it is really severe and obvious. In that case you might see and abrupt change in density such as at the depth of a moldboard plow or disc. It might show up as a reduction in rooting depth, roots moving laterally, or a noticeable reduction in the size of roots indicating an inability to easily move below the compacted layer. With the trowel, you typically want to just poke at the soil profile and break out small chunks, and look for changes such as a platey, closely layered structure. Spring is not a particularly good time to do this because the soil is typically very moist and the wetness lubricates the soil particles and masks the changes. It is probably easier later in the summer when the soil is drier.

It helps to have a bigger hole to work in so a back hoe is nice. In drier soil you may notice compacted soils have coalesced into large clods that would have to be broken down with additional tillage. One thing you could do is dig in an alternate location in a fence row, a place that has not been tillage and trafficked frequently. That would give you a point of reference for what those soils might look like in a more ideal state.

It helps to have more long-term knowledge of the soils. Some soils set up so tight that they really need periodic subsoil tillage for many crops, but that is not at all typical. It is easier to look at growing crops and the soil surface to find areas that appear to be affected by compaction or poor soil structure. Typical would be poor infiltration, although many soils infiltrate poorly even when not compacted by equipment or traffic, stunted plants indicating poor root development or oxygen stress from excessive moisture, crusting surface after rain, areas quick to moisture stress in dry conditions, etc. Of course, these mimic other problems as well so just because you notice these things it does not mean the you need to subsoil, at least not on a regular basis.

I the case you mention, where the farmers think the field may need to be subsoiled, you should trust their judgement. Go ahead and subsoil the entire field, it is a relatively small area, and put in place a cropping program that will build soil quality. If in a few years you sense that subsoiling may be beneficial, try to deep till some strips and not others so you can see if it has a positive effect. For instance, if possible, do the deep tillage in strips east to west, and plant your vegetables over the top in rows north to south. That will give you a good sense of the result of deep tilling. The reason you need to do this is that the effect of deep tillage can be highly dependent on the weather, particularly in a wet year. But you really want to know the effect over all years, so you have to have something to compare it to. I do not think you want to have deep tillage as a regular part of your cropping program unless you have a clear reason to do it. It is not really draft-animal friendly work for most folks, and you may be better off putting scarce resources to use in other ways.

Soil quality, ‘health’, requires a balance of the physical, chemical and biological factor of the soil. Physical properties like aggregate stability and infiltration you can see and influence with tillage. Chemical factors like pH and nutrients you can measure with a soil test. Biological factors are harder to measure and interpret but if you take care of the physical and chemical components the biology can develop. Indicators of soil quality include soil pH, soil organic matter (SOM) and soil properties that are related to soil organic matter such as macro-aggregate stability. These are things that develop over time in response to the cropping program, soils, etc. It often takes five years or more to measure significant changes in soil organic carbon, aggregate stability, etc

It is your call on how or if you want to use these health assessments. I think tests for soil microbial respiration are going to cost about $100 each, although I admit I have not looked at the Cornell stuff. It is important to try to sample at the same time each year, and as close to the same location each year as possible. The results will be influenced by soil moisture, temperature, etc so it would be good to consider your field operations as far as the timing. For instance, if you will be spring plowing and planting about the same time, you may want to sample a few weeks after planting each year. It would not be a good idea to sample one year before plowing and after planting the next. Same with manure applications, etc. Also, the test probably has some procedures regarding soil moisture. Personally, I would not bother with these tests at this point unless you want a record of changes over time. They and expensive and they will not give you much practical information about what to do next.

There is a lot involved with soil biology. Basically, reduce tillage intensity, use cover crops to maintain an active root systems for as long as possible throughout the year, use rotations that will provide a balance of pests and pathogens, cover crops help in this by essentially extending the crop rotation, add additional organic inputs such as manure or compost to the extent that you can keep soil chemistry from getting out of whack, and make use of botanical diversity with mixes of grasses and legumes when possible. I know intensive tillage (moldboard plowing) is common in vegetable production, so shallow plowing is probably best. You just have to develop a system that works for you keeping the fundamental principles in mind. If you do these things, the soil biology will take care of itself. Not that you cannot influence it. Certain cover crops such as oilseed radish and oriental mustard have biosuppressive properties that have importance in biological systems and you will want to learn about those. But it is not as simple as it seems. Here is a link to an article I wrote recently with a colleague regarding N cycling with cover crops in corn production. http://news.msue.msu.edu/news/article/building_soil_quality_with_an_oilseed_radish_cover_cropwhere_did_the_n_go
This issue of soil biology is quite involved and not real well understood, at least from the point of practical management in a production system. I guess that is why it is so interesting.

[newbeatfarm]

I went to a info session on the Cornell Soil Health test you speak of a few years ago. It seems like a good test to periodiaclly pair with a soil test to get a better idea of what nutrients are actually avaialbe to your crops in the field and how they respond to them. May times soil test just give you data on the amount of certain nutirents in the soil and not the amount of these nutrients that are actually available to the plants. I might be most apt to take one of these test once the soil had warmed up late spring when the microbial life in the soil would be more active. As far as standard soil tests, I am not familiar with the soil testing company Brookside you referred to Erika, but would suggest Lancaster Agriculture Products http://www.lancasterag.com/Testing.html. Their analysis gives you information on what is actually available to your plants. Along with that, their prices on soil amendments are terrific and they will make custom blends for you. I ship pallets all the way from them up to Maine and it is still more affordable than my local supplier who does notmake custom blends. Great to hear all of this discussion on soil health. -Adrienne

[Tim Harrigan]

@dominiquer60 34100 wrote:

I understand that this test is a snapshot like Tim states, however is there an ideal time of the spring, soil moisture or tillage condition that one should take into consideration when taking samples for a test like this?

Erika, I am not sure I was clear about this. I assumed this is a measure of soil microbial respiration. I said do the test a few weeks after planting. That was to give the soil a chance to settle after tillage and planting, and to warm up. Warm, moist soils will be most active so this test probably involves some measures of water infiltration a day or two before taking the soil sample. If you want to track changes over time the key is consistency of timing and location.

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