Agronomic tools of the trade
Are they tools or toys?
April 15, 2008 By Karen Dallimore
Are they tools or toys? You know,
all those field gadgets that you didn’t know you needed? Believe it or
not, there are a couple of agronomists at the Ontario Ministry of
Agriculture and Food whose job it is to evaluate the latest field
gadgetry to find out what works and what doesn’t.
|Elaine Roddy demonstrates one of several field gadgets being marketed to farmers.
Photo by Karen Dallimore.
Are they tools or toys? You know, all those field gadgets that you didn’t know you needed? Believe it or not, there are a couple of agronomists at the Ontario Ministry of Agriculture and Food whose job it is to evaluate the latest field gadgetry to find out what works and what doesn’t.
Agronomists Elaine Roddy and Anne Verhallen work out of Ridgetown College. The pair teamed up to review some of their tool testing findings at the 3rd Annual OMAF Integrated Pest Management Technical Update meeting.
Soil moisture monitoring equipment, quick nitrogen tests, chlorophyll meters, portable pH meters and compaction meters to name just a few – all “must haves” according to the manufacturers. But are you wasting your money?
Looking at each one of these in turn, Verhallen began with soil moisture monitoring equipment. Why worry about measuring soil moisture? Often growers wait too long to start irrigating, she explained. Often they don’t put on enough water, and with drip irrigation it is sometimes too easy to turn them on.
The tensiometer measures how hard it is for the plant to get water. According to Verhallen, it is tried and true. They do require maintenance and only measure a limited area. Prices fall in the $100 range, although you may need more than one for each field. The nice thing about them is that anybody can read them.
A revision of some older tensiometer technology is called the Watermark, and the accuracy of this tool may be a little more dependent on your site selection. It is a little bit slower to respond to change than the tensiometer because it needs time to equilibrate. The life span is three to four years, and they are low profile, so they escape damage from the cultivator.
The newer technology is called TDR or Time Domain Reflectrometry. It will give you measurements immediately that can then be downloaded to a computer. It is very accurate and commonly used in research, but it is also relatively expensive at about $300 per unit. One drawback is that when you put it in the ground, you are then taking measurements in disturbed soil, which is not what the roots are in. The tool itself has been relatively robust; if you are working with moist soils, the TDR meter should last a while. Another version of the TDR comes as a hand-held model, and while it does a good job, at about $1,600 it is fairly expensive.
The next tool they evaluated was the soil nitrogen quick tests. One is the Cardy meter retailing for about $400, and there’s also N-check strips, which are a one-time test fashioned after swimming pool test strips. For both of these, you will need to mix a soil sample with a commercial extraction, filter it out and test the filtered water.
The Cardy gave pretty poor results while the N-check strips were only slightly more reliable, but Roddy was concerned their methodology of testing might have been the culprit, not the tools. They followed instructions to the point, but did the recommended microwaving of the soil drive out some of the nitrogen? What about the calibration of the meter itself – was it satisfactory? Stay tuned – testing will continue.
Another tool is called a SPAD meter. It’s basically just reading the chlorophyll content of leaves, explained Roddy. It is not very sensitive, but it can be useful if there is either a very under-fertilized or very over-fertilized check strip in the field and the field readings are compared to the check strip. In extreme cases you will see differences. “We don’t have any strong benchmarks yet as to making recommendations based on the chlorophyll meter,” said the tool testing team.
The final tools they evaluated were hand-held pH meters. Why do you need them? These can be used as a quick test in the field as a problem-solving tool, explained Verhallen. At least with field vegetables, if there are strange problems that are not insect or disease based, often it comes down to pH or salt causing problems in the field. As well, if you are seeing patches of carryover of herbicides, quite often it may be the pH contributing to the problem.
Some of the meters didn’t fare so well, she reports. There’s a popular hand-held model for $12 from Canadian Tire that is garbage. Another retails for between $65 and $100, depending on where you get it, and has found its calling as an expensive paperweight. “It’s not worth the money you paid,” reports Verhallen.
A few of the pH meters that passed the test include the Twin pH meter that checks in at the $400 range – a little pricey but it gave good correlation of results between the field and the lab. The pHTester 2 was also perfectly functional, although calibration takes some time.
The simple calibration of the pH Pro made it one of Verhallen’s personal favourites. It cleans up nicely and packs up conveniently so it’s ready to go when you need it. The pHep measures the pH of irrigation and spray water as well as soil and is not horribly expensive. It works well but it does require double calibration.
And finally, Roddy had a look at soil compaction probes. The problem with the probe itself is that, “if you lean on it hard enough, you can make it do anything. If you are looking for compaction, you will find it.” She has found the best way to use such probes is to close your eyes and feel the compaction. “Spending extra money for the dial on the end of the stick is probably not worth it,” and she has found that a welded rod like a tile probe works just as well. “To me, of all the tools we’ve talked about today,” said Roddy as she held up a welded compaction probe, “this has been the most valuable one.”
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