Day 51 - SOM testing, glyphosate & pH

I spent the day today with Michael Eyres, from Injekta Systems, who has organised the last couple of visits for me. He's a soil agronomist, which basically means he advises on how best to get nutrition into plants according to what type of soil you have on your farm. We drove up to Jamestown to see one of his clients, who has just taken on a new piece of land that he wanted testing.Michael is meticulous in his soil sampling technique, and he will make sure that each individual layer is tested separately. Often he will spend a day digging proper pits, but this was a quicky so they just took little core samples. This particular farm has two very distinct  layers within the top 10cm or so. The top 5cm is particularly high in potassium which makes the clay particles stick together very closely - an artefact that is apparently often blamed on compaction caused by sheep grazing. When this bit is crumbled by hand it turns into a very fine, almost dusty, powder. The second layer is higher in magnesium, and forms into harder, but more distinct lumps. Beneath this is a high magnesium clay layer, which when dry is very, very hard. This soil type is more suited to tine type direct drills, as it is beneficial to have a cultivation effect to break up the top crust.Back in June I wrote a little bit about the common way of testing for SOM (Soil Organic Matter), which is the LOI (Loss On Ignition) test. This is done by burning the sample, and then seeing how much less it weighs afterwards. Anything that has gone is assumed to be SOM. This can be problematic, as it does not distinguish between a piece of fresh straw and older, more stable forms of soil carbon (humus, not humous). Here in Australia they use a test called Walkley-Black. The difference is that the sample is put through a very fine, 0.42mm, sieve first of all to take out larger (and presumably un-decomposed) items, and then... well it's easier if you read it here;

The method measures the amount of carbon in plant and animal remains, including soil humus but not charcoal or coal...

Oxidisable matter in the soil is oxidised by 1 N K2Cr2O7 solution. The reaction is assisted by the heat generated when two volumes of H2SO4 are mixed with one volume of the dichromate. The remaining dichromate is titrated with ferrous sulphate. The titre is inversely related to the amount of C present in the soil sample.

So there you have it. I don't know if the result is actually more accurate than LOI, but it seems like it should be.

A further point of interest that came up was the efficacy of glyphosate (Roundup) in hard water. It's something that has been on my mind for the last year, but I've not yet been proactive enough to actually do anything about it. According to Michael, the optimum pH for glyphosate is 3.2. This is much lower than our water, which I guess would be about 8. The problem is that in hard water the calcium ions bind with the active ingredients, making them less effective. He recommends the cool (no pun intended) sounding "Glacial Acetic Acid" to bring down the pH. It's fairly easy to get hold of, so I have no excuse for not giving it a go. It's also worth noting that, even at low pHs, it is still necessary to use ammonium sulphate water conditions to get the best effect, as this helps out in a different way to simply changing pH.The farmer we visited has a 3 year old Conserva Pak drill, which is rigged up with a Liquid Systems (see yesterday's blog) pump. The seed cart, which weighs 15t when full, has 3 sections. The largest is for solid fertiliser, which is straight MAP for legumes, or an MAP/Urea blend for cereals and OSR. The next compartment is for seed, and the smallest is for the liquid trace elements, and also inoculants for legumes and fungicides for OSR. The liquid tank actually started life as a solid fertiliser hopper, but was sprayed inside with a polymer to waterproof it, and then just had a metering system fitted on the bottom. You can see it fairly clearly in the picture above. The Conserva Pak drill works by putting solid fertiliser down behind the front tine, and then the seed goes down the back leg. The liquid goes in the same trench as the seed, again you can see it clearly in the picture.I played some Aussie Rules this evening, but there are no pictures, probably because I was only allowed on the pitch for about 3 minutes. Bloody Poms.