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Weed control, management, ecology, and minutia
by Chang Thao
on April 28, 2015 at 2:20 AM
Interesting. So how would I estimate herbicide concentration if I apply it to a volume of soil like a garden box? Let's assume it's 1sqft and 4 inches deep. the soil is a sandy loam.
by Brad Hanson
on April 28, 2015 at 8:32 AM
Hi Chang,  
Lets' take your example of a 1 sq ft by 4 inch (1/3 ft) garden bed and combine it with the soil bulk density of 100 lb/ cubic foot in the 4th bullet in the post above. Based on that, your (very small) bed will have about 33 lbs of soil (1 sq ft x 0.33 ft deep x 100 lbs).  
However, to estimate the initial herbicide concentration in that amount of soil, we'd need one more piece of information which is the herbicide application rate. With this information, usually expressed on a per acre basis for large scale applications or on a per 1000 sq ft scale for smaller applications, it is relatively simple to calculate how much formulated product was applied per square foot. From there, you can use the percentage active ingredient in the formulated product to figure out how many lbs of herbicide active ingredient could be distributed in the 33 lbs of soil in your example.  
So, let's go back to my example above. Assuming you applied a herbicide at a 4 lb ai/A rate - 4 lb/A x A/43560 sq ft x 33 lb (1sq ft x 0.33 ft x 100lb) = approximately 0.00000278 lb active ingredient per lb soil or 2.78 ppm.  
Of course if you applied a lower use rate product, say 1 lb ai/A, your starting concentration would be 1/4 of that or 0.69 ppm  
Hope that helps you with your estimation.  
by Maduike, E.
on November 26, 2015 at 1:42 PM
Help pls!  
How can I determine the herbicide concentration in the soil based on the following information :  
- Active ingredient = 50% SC per L  
- Application rate = 4L/ha  
- Area of micrcosm applied = 0.25m square  
- Depth of soil examined = 10cm  
- Spray volume = 1L  
- Volume of herbicide diluted = 10ml  
- Soil type = Sand(46.8%), Clay(27.2%), Silt(26.0%)
by Brad Hanson
on November 30, 2015 at 10:50 AM
I don't think we can quite figure this out from the info provided. The first note of the AI being 50% SC per L doesn't sound correct to me. If it's a liquid formulation (an SC) then it should have a weight of AI per volume (g/L or lb/gal or similar). If it's a solid material, like a WDG, it could be a % but wouldn't be per liter.  
That being said, here's the mathematical steps I'd take:  
1 1 L product has ____ g of AI (you're missing this information)  
- 4 L product per hectare  
- 1 hectare = 10,000 sq meters  
- 0.25 sq meters per microcosm  
- one microcosm has 25,000 cubic centimeters (25 x 25 x 10 deep)  
- 1 cubic centimeter weighs about 1.5 g (from the range in the post above, you can correct if you more about your specific soil)  
If you can figure out how many grams of AI in your herbicide product, you can multiply through all these conversions and end up a reasonable estimate of grams of AI per gram of soil.  
Good luck.  
by Maduike, E.
on December 8, 2015 at 3:55 PM
RE: My post on Nov. 26th 2015.  
Actually the herbicide is atrazine (Atraforce) sold as a liquid formulation in 1L container. On the container it's written " Active ingredient = Atrazine 50% SC. " 10ml of the herbicide was diluted in 1L clean water and was sprayed on soil dimension of 0.5m x 0.5m (0.25m square). Using the initial information provided, how can I determine the herbicide concentration in the soil at 10cm depth.
Reply by Brad Hanson
on December 8, 2015 at 6:55 PM
So with the trade name provided, I was able to find out a little bit of information (although still far from complete). Atraforce appears to be an atrazine formulation with most manufacture in China and most uses appear to be in Nigeria. 50% SC still is incomplete information, in my opinion, because we need a wt (of crystalline atrazine) per volume (of the liquid). I could not find this for Atraforce, but I did find a notation for another atrazine 50SC that suggested that this means a 500 gram ai per liter formulation. This is not standard nomenclature to me, but it makes sense as that's similar to the atrazine formulations we use in North America. So we'll use it for this exercise.  
1. You have 500 g of atrazine per 1000mL of Atraforce (500SC)  
2. You applied 10 mL of Atrafoce to your plot (the spray dilution doesn't matter in this case).  
3. Mathematically, you applied 5 grams of atrazine to the area.  
4. We calculated earlier that you probably have just under 10,000 grams of soil in your plot (25cm x 25 cm x 10 cm deep x 1.5 g per cm3 = 9375 g). Let's use 10,000 g for easy calculation  
5. So, you would have started with about 5 g atrazine in 10,000 g of soil.  
6. Scale this up to 5 divided by 10,000 is 0.00005 g atrazine per gram soil.  
7. More conventionally, you'd scale this to parts per million which gives you an estimated starting herbicide concentration of roughly 500 parts per million (ppm).
by Maduike, E.
on March 29, 2016 at 5:39 AM
Pls what is the concentration in mg/L when 0.2ml of atrazine (Atraforce) is diluted in 1000ml of water?
by Brad Hanson
on March 29, 2016 at 8:20 AM
If you have 0.2 mL of a product that has 500 g ai per liter (my assumption from above since I could not confirm the concentration of Atraforce. Diluted in 1 liter of water this should be 100 mg ai/liter. Here's my math:  
(0.2 ml Atraforce / 1 L water) x (500 g atrazine ai/ 1 L Atraforce) x (1000 mg ai atrazine / 1 g atrazine ) = 100 mg atrazine ai per 1 L water.
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