Mathematics help

[RickH]

Any mathematicians here ?
Thinking of using a High Phosphours feed for my lawn.

I want to apply from constant ratio applicator (Aquamix) which I can set to 0.2% / 0.5% / 1.0% / 2.0% ... that is the % of liquid feed to water.
The feed is in soluble granules, so I would need to pre-mix with water.
Application rate required is 0.1% - 0.5%

I need to figure out what strength of mix should I create ( how many grms to Litre water) to put into the applicator and then what % rate do I set on Aquamix.
It's not working in my head.

Best I could think was make a 10% mix and set Aquamix to 2% and that would give me 10 x 2% = 0.2%
Or is this flawed.

 

[MNW67]

Do you have a link to the lawn feed dilution instructions?

 

[robinbanks]

That works for me; you're making up a solution that is 10% feed
And you're then telling your diluter to put 2% of this mix in with the rest water, so the actual amount of feed going into the lawn is 0.2%

How do you know how many grams gives you a 10% mix?

If the instructions for the feed are in grams per sq metre you might need to tweak a bit, do some tests to see how fast your diluter chews through the liquid feed, so you know for your eg 100sqm garden needing 100 grams of product, and you've mixed up 1litre of feed using 10 grams and it's gone in 1 minute of running the diluter, you need to be mixing up 10 litres with 100g and watering the garden in 10 minutes (or 5 litres in 5 mins etc)

 

[RickH]

I have a constant ratio applicator that I can set to 0.2% / 0.5% / 1.0% / 2.0%
It's how much I mix with water to create the solution to use with applicator that is making my head hurt
The instructions are :

Application Rates:​

Liquid Feed Application:​

Used in the same way as other water-soluble fertilisers. Feed is usually applied via a normal watering can. Simply add the appropriate amount of Feed to the can, add water and apply liberally to the plant root area. A very approximate guide is 5 litres per square metre. Feed is best applied as a liquid feed whilst the plant is actively growing. Ideally alongside watering. The standard rate is 1g / litre of water. However this can vary anywhere between 0.5g / litre – 2g / litre. Use the lower rates for sensitive plants, such as pot plants under glass. The higher rates should be used on rapidly growing plants in outdoor soils. DO NOT exceed 2g / litre.

​

 

[MNW67]

@RickH

The recommended standard dilution for the lawn feed granules seems to be 1g per litre of water.

But the solution you make up from the lawn feed granules is then diluted further by the Aquamix.

The maximum the Aquamix will allow is 2% liquid lawn feed/water. That means a dilution of fifty times.

So, I would say that you need to add 50g of granules to each litre of water in order to get a final spray onto the lawn of 1g per litre. This assumes you are using the 2% setting on the Aquamix.

I will be grateful if others will check this, though!

 

[RickH]

@RickH

The recommended standard dilution for the lawn feed granules seems to be 1g per litre of water.

But the solution you make up from the lawn feed granules is then diluted further by the Aquamix.

The maximum the Aquamix will allow is 2% liquid lawn feed/water. That means a dilution of fifty times.

So, I would say that you need to add 50g of granules to each litre of water in order to get a final spray onto the lawn of 1g per litre. This assumes you are using the 2% setting on the Aquamix.

I will be grateful if others will check this, though!

Glad you understand what I'm trying to achieve .... if nobody refutes this I'll go with that figure - Thanks, appreciated.

 

[robinbanks]

I actually disagree with what MNW is proposing because it doesn't consider the area and you're using a hosepipe of unknown delivery rate which is deleting the only factor you did formerly know; the amount of water you're mixing up in a watering can. You can't spray the garden and then, by eye, look at it and say "yep, I've delivered 5 litres of water per square metre there"

The instructions say the feed has an application rate of approx 5g per square metre.
Say your lawn has an area of 124 square metres, you could put 620g of feed in 2.63 litres of water, set the Aquamix on 0.5% and spend 7minutes 48 seconds watering the garden. The only thing that matters is that from start to finish you've watered at an even rate and what ever volume of feed in the Aquamix has been entirely consumed, thus achieving a dispense of 5g per square metre (1g per litre, 5l per sqm)

I propose you put a known volume of water in the Aquamix and set it on a medium setting. Water the garden at a good pace and see how much water has been consumed from the dispenser. If you run out, lower the setting. If only a tiny amount of water is consumed raise the setting. Try and be consistent about the rate you water the garden

Now measure the size of your garden in sqm, and put that amount of grams of feed in the amount of water you consumed from the feeder (adding the feed might make the liquid thicker and emit slower, there could be a bit of trial and error here) and then water your garden at the same good rate as you did, aiming to consume all the prepared feed mix by the end of the job

You will thus have dispensed eg 620g grams of feed into your 120sqm garden, and achieved the 5g per sqm outlined in the instructions

(I do find the instructions something of a nonsense, because they go into great and accurate detail about the concentration of solution in therms of grams per litre to mix up and then are only "very approximate" about how widely the solution should be spread, which is daft. If you mix up X and then spread it over 100sqm its a massively different feed rate to mixing up X and pouring it all on 1sqm)

 

[MNW67]

Glad you understand what I'm trying to achieve .... if nobody refutes this I'll go with that figure - Thanks, appreciated.

(I do find the instructions something of a nonsense, because they go into great and accurate detail about the concentration of solution in therms of grams per litre to mix up and then are only "very approximate" about how widely the solution should be spread, which is daft. If you mix up X and then spread it over 100sqm its a massively different feed rate to mixing up X and pouring it all on 1sqm)

I agree about the instructions. I was doing the easy calculation to get the correct dilution. How you then go about measuring how much you actually spray on each square metre of lawn is a different matter!

I suppose another way is to test the flow rate of the Aquamix by timing how long it takes to fill a bucket.

 

[RickH]

I agree about the instructions. I was doing the easy calculation to get the correct dilution. How you then go about measuring how much you actually spray on each square metre of lawn is a different matter!

I suppose another way is to test the flow rate of the Aquamix by timing how long it takes to fill a bucket.

I'll check flow rate this morning .... but in reality flow can change as other users on same water feed use water ... pressure drops

 

[RickH]

Just checked .. flow rate is 8.8L/min, but to be honest It's not that critical, as long as 'mix strength is right' I'll simply water it in.

So

You can't spray the garden and then, by eye, look at it and say "yep, I've delivered 5 litres of water per square metre there"

In practice though that is what happens you water until all soaked, without ponding.
Agree if a I used watering cans it would be a know volume of mix applied but don't want to be carrying 45 cans of water.
As I know flow rate, I could simply time how long it takes to do whole area and figure out if I need to go over another once or twice.

 

[RickH]

I actually disagree with what MNW is proposing because it doesn't consider the area and you're using a hosepipe of unknown delivery rate which is deleting the only factor you did formerly know; the amount of water you're mixing up in a watering can. You can't spray the garden and then, by eye, look at it and say "yep, I've delivered 5 litres of water per square metre there"

The instructions say the feed has an application rate of approx 5g per square metre.
Say your lawn has an area of 124 square metres, you could put 620g of feed in 2.63 litres of water, set the Aquamix on 0.5% and spend 7minutes 48 seconds watering the garden. The only thing that matters is that from start to finish you've watered at an even rate and what ever volume of feed in the Aquamix has been entirely consumed, thus achieving a dispense of 5g per square metre (1g per litre, 5l per sqm)

I propose you put a known volume of water in the Aquamix and set it on a medium setting. Water the garden at a good pace and see how much water has been consumed from the dispenser. If you run out, lower the setting. If only a tiny amount of water is consumed raise the setting. Try and be consistent about the rate you water the garden

Now measure the size of your garden in sqm, and put that amount of grams of feed in the amount of water you consumed from the feeder (adding the feed might make the liquid thicker and emit slower, there could be a bit of trial and error here) and then water your garden at the same good rate as you did, aiming to consume all the prepared feed mix by the end of the job

You will thus have dispensed eg 620g grams of feed into your 120sqm garden, and achieved the 5g per sqm outlined in the instructions

(I do find the instructions something of a nonsense, because they go into great and accurate detail about the concentration of solution in therms of grams per litre to mix up and then are only "very approximate" about how widely the solution should be spread, which is daft. If you mix up X and then spread it over 100sqm its a massively different feed rate to mixing up X and pouring it all on 1sqm)

 

[RickH]

Update ... Aquamix support now responded - thought I'd post it here for help for anyone else....


With the Aquamix setting to 1%, it draws 10ml of concentrate into 1 litre of water.
To ultimately have 1g of dissolved granules in 1 litre of water, the 10ml drawn in must contain 1g of granules.
Extrapolated, this means that we dissolve exactly 100 grams of granules per 1 litre of water and then pour that into the Aquamix.

If you wanted a 0.05% solution with the Aquamix set to 1%, they only need to dissolve 50g in 1 litre of water.

 

[robinbanks]

I still say you're better off watering the garden as you would, and looking how much is dispensed, then mix your feed in so that it's dispensed to the required grams-per-square-metre

All this back and forthing about the concentration of the solution is still a level disconnected from the feed rate per unit area..

In practice though that is what happens you water until all soaked, without ponding.

But you can't look at a patch of wet soil and tell me how many litres of water it contains; it might be a litre making the top mm dark brown or it might be 10 litres making the top 10mm dark brown
If you've had your Aquamix running to perform it, you might be ten times over the feed rate you wanted..

By all means time it, use your flow rate, your dissolution rate.. you still need the area of the garden to know if you're over feeding.. and when you've combined all the bits of info and worked the maths through you'll come round in a circle to what I'm proposing; area of garden gives grams of feed required, time required to water gives volume of feed dispensed, gives grams of feed into volume..

 

[Justin Passing]

Use a measuring jug and water some easy percentage of the lawn, or one square metre...?

 

[RickH]

I still say you're better off watering the garden as you would, and looking how much is dispensed, then mix your feed in so that it's dispensed to the required grams-per-square-metre

I will follow Aquamix manufacturers advice on calculating what strength to use, I’ll also follow your suggestion to check how much I use to fully water … together provides best approach.
I’ll only do this once though just so I have a guide.