Day 37

Screen Shot 2014-07-04 at 07.42.57The last day, and another hastily arranged appointment. I’ve mentioned the Haney soil test in previous blogs, and today I visited Ward Laboratories to see how they do it.

The Haney test has some overlap with conventional soil tests, but it is designed to determine more precisely how much nitrogen and phosphorus will be made available to growing plants through biological activity, not just what is physically present. One of the ways this is accomplished is by using a weaker acid solution to extract the nutrients, which is supposed to be closer to the conditions roots grow in, compared to conventional tests, like Olsen P.

Total carbon, nitrogen and phosphate are measured, as well as their inorganic fractions. When you subtract inorganic from total, you end up with the organic fraction. Inorganic nitrogen is easily leachable, and so if there are high levels they would recommend grass based cover crops to try and capture some of it.

The ratio of organic carbon to organic nitrogen is important, as if it is above 20:1 then no nitrogen or phosphorus will be released through microbial activity. In this situation they would recommend cover crops with higher proportions of legumes to bring the ratio down to between 15:1 and 8:1.IMG_3302

Another novel part of this regimen is the Solvita CO2 burst test. This measures the amount of CO2 produced by 40g of soil in a 24hr period. The idea is that more CO2 = more microbial activity & biomass. They claim that this is highly correlated with overall soil fertility.

All of these tests are combined to come up with a “Soil Health Calculation” score. For completeness, here is the formula: (Try and remember it, there’ll be a test next week)

Solvita CO2 / organic C:N + (organic carbon/100) + (organic nitrogen/10)

The score goes from 0 upwards. A conventionally tilled soil with little or no crop rotation, cover crops, livestock etc may score as low as 2. At the other end of the scale, Gabe Brown’s soil is normally in the high 20s, and they have had a few results in the low 30s. The printout for each sample includes what the results would have been from a conventional test, which in the case of nitrogen is usually less as it has not accounted for the organic forms. This should supposedly allow the application of less nitrogen (if your soils are fertile), and therefore save money.

Interestingly, they claim that with cover crops, the scores are significantly increased as the mixes become more diverse. It does make sense, as presumably different root exudates will feed different microbes, and the total quantity will increase. They also warned that there is normally a 6-12 month lag in seeing improvements after cover cropping, as it takes this long for the biology to work its magic, and make the nutrients available. This would confirm our experience, as well as backing up Fredric Thomas, who sees a gradual decline in the amount of nitrogen he has to apply on his farm in France.

Does is work? Rick Haney, who invented it, is currently analysing yield data from farmers all over the US and trying to correlate it to actual crop performance. I think it is an interesting idea, and may be a useful management tool to at least show that one is moving in the right direction. The test costs $49.50, and I’m going to send in some samples in due course. If anyone else is interested, get in touch and we could maybe combine a shipment.

But that’s it for now, I’m due at the airport in a couple of hours.

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