farm soil

Soil testing at the new property - part 1

Apr 11, 2012by Farmer Liz

After we found out that the new property was ours, the first job was to organise some soil samples. As the property has about 60 acres that has been cleared and contoured for cultivation we want to have a go at planting some crops to make hay. There is one area of about 30 acres at the top of the ridge and another separate area of about 30 acres lower down, so we call them the upper and lower cultivation areas (boring I know, we’ll come up with something better eventually!). The rest of the property will be used to fatten steers, and extra hay can get them fat even faster, so we think its worth a try. We were able to buy some secondhand ploughing implements from the property vendors, and we have just purchased a tractor (post about that coming), so that will get us started and we can decide from there if its really worth the work.

We don’t want to use conventional farming methods at all, especially as we can see the negative effects on the land in the cultivation area which has been farmed conventionally for the past 10-15 years. Currently only one small section has a planted crop of forage sorghum and the rest is covered in every weed imaginable. Even though we have had plenty of rain, the weeds aren’t exactly thriving, they are just a low ground cover, with some saplings coming through, so we assume that these areas haven’t been ploughed for at least a year.

If we were going to be living on the property full time, we would arrange to have lots of chickens up there in tractors, with mesh electric fencing to keep out predators, and leave them to scratch up all the weeds and add some much needed fertility to the soil. We have seen amazing improvements at “eight acres” where the chicken tractors have been, so we are hoping to eventually apply the same methods at the big property. The aim is to let nature/animals do the work! Unfortunately it will be a few years until we can build a house there, so we need to come up with another solution in the meantime. Our best option is some form of organic fertiliser to both increase the organic matter in the soil and add minerals.

The first step is soil testing of the area. We need to know which minerals are deficient so that we can begin to correct this, otherwise our crops will be weak, suffer from diseases and not provide complete nutrition for our animals. The other day we went out to the property with a couple of buckets, ziplock bags and high-tech soil sampler (length of pipe and a mallet) that I described in a previous post. We took samples from several locations within the cultivation areas.

Last time we sent the samples for “eight acres” away to APALfor a full analysis and report, and I was very happy with the results. At that time we really wanted to know which minerals were missing from our pasture to make sure that the cattle were getting everything they needed. We found out that the soil was deficient in calcium and copper, so we started to feed those minerals to the cattle. This time, because we are planning to plant crops, we decided to do a few of our own tests to learn more about our new soil and to help us decide which samples to send away. As we had two large areas, that are split up into 3 contours each, we wanted to see if there was a significant difference between the contours, and whether we should send a sample from each contour, or if one sample could represent the entire cultivation area.

Anyone who went to university with me will remember how much I hated soil science! I think we only studied it for a few weeks, but I complained bitterly that it was totally pointless and unnecessary for my Chemical Engineering degree (same can be said for food microbiology, and these are the two subjects that I now use most for farming!). The three things that I learnt during that time are:

Soil structure – whether the soil forms aggregates or dust
Soil texture – soil consists of sand, silt, clay and organic matter
Farming required added chemicals – we used the pH to calculate how much chemical to add per acre

I don’t think we discussed soil minerals or microbiology at all, but I may have been asleep during those lectures. I have since learnt that while nitrogen, phosphorous and potassium (NPK) are important to plant growth (and therefore the main components of fertiliser) all minerals are needed to some extent for healthy plant growth (just like healthy human growth!), and soil microbes (and other soil life such as earthworms) are needed to help to convert organic matter into nutrients that can be used by plants. When agricultural chemicals, such as fertiliser, herbicides and pesticides are used on crops and pasture, they kill the microbes, so the soil is effectively dead and just a medium for fertiliser to be transmitted to the plants. As we dug the samples, we noticed that there were no earth worms in any of the sample holes, so we are pretty sure that there isn’t much life in this soil. For comparison, when I dig in my garden, I usually find 2-3 worms per trowel. It is ridiculous that we disrupt a natural system that works, resulting in plants that depend on us for expensive inputs, when the original system worked for free!

After reading a fair bit on this subject, but not being an expert at all, as far as I know, the important aspects of soil from a cultivation point of view are:

soil texture
soil minerals
soil microbiology

We can test the structure ourselves, so these are the tests we did at home to start to understand our soil. We then sent some samples to be tested for mineral content. The microbiology is quite obvious from observing visible life in the soil, the colour of the soil and what's growing above the soil. In this case it is clearly lacking.

There is lots of information on the net about these tests, a good example is here.

bags of soil for home testing

Soil texture

We used two tests for soil texture. The first is the “manipulative test”. The more clay in the soil, the easier it is to roll a small amount between both hands to form a sausage (this is quite fun). We found that the upper cultivation area soil would not roll into a stable sausage, whereas the lower cultivation soil did. Note that even if you add more water to the upper cultivation soil, you just smear more on your hands and do not form a sausage. This indicates higher clay content in the lower cultivation area, so it will probably be more difficult to plough (being heavier) and hold water for longer compared to the upper cultivation area.

comparing structure, composition and pH across samples

The next test was for soil composition. We placed soil in a glass jar, about half way filling the jar with soil and then topping up near to the top of the glass with rain water. We shook the jar and then allowed the soil/water mixture to settle. The sand settles to the bottom and the silt forms a layer on top of the sand. The clay is suspended in the water, with the organic matter floating on top. We can use this to compare the actual ratios of sand/silt/clay in each sample to determine the soil type. Again, there was more sand and silt in the upper cultivation area.

soil composition

Soil pH

We bought a pH test ages ago for the garden soil. Its pretty rough, as it depends on interpretation of a colour chart, but was clear that all our samples had a pH between 5.5 and 6. This is low, and we can decide how to correct this when we see the mineral analysis, although Peter Andrews reckons that this will correct itself as the fertility improves and the plants begin to "unlock" the minerals in the soil, so we may not do anything at first, just be aware that some plants wont do well at low pH. Joel Salatin has a theory about decay of organic matter producing carbonic acid, which dissolves the minerals in the sand/rocks in the soil to make them available to plants, I don't know if this is true, but it does sound sensible.

The pH test

In the next part, I'll write about testing for Dispersion and Slaking and Permeability, then I'll discuss the results of our mineral testing in the final part.