TREATED HECTARES AND FIELD HECTARES. SPRAY VOLUMES AND APPLICATION RATES.

TREATED HECTARES AND FIELD HECTARES. SPRAY VOLUMES AND APPLICATION RATES.

Treated Hectare = ha_t Field Hectare = ha_f    Make sure you understand the difference.

A treated hectare is 10'000 m² i.e. all 10'000 m² of a field are treated.   Although a crop occupies a field hectare in many cases only a portion of each field hectare is actually treated. I'm merely using tobacco as a row crop example.    It could be minimum tillage in maize, corn, "mielies", sugarcane, peas, beans, cotton, casava, or even gum or pine trees.

A PRACTICAL EXAMPLE - TOBACCO - TREATING FOR BOLLWORM

You need to know the following.   Ridge spacing 1.3 metres. Walking speed if using a knapsack = 3 km per hour. (3'000 metres per hour or 50 m per minute). Insecticide application in 120 litres per treated hectare - ha_t The insecticide is sprayed in a narrow band over the row to ensure coverage of the tobacco seedling crown. That's where the moth lays the eggs. The spray width will be 20cm or 0.2 metres.

How many ridges for every field hectare? One side of a hectare is 100 metres wide and there's a ridge every 1.3 m = 100 divided by 1.3 m. = 76 ridges. There's a bit of variation here between farmers so let just say 75 ridges. For each field hectare there'll be 75 ridges each 100 metres long.

Total length for each field hectare 75 ridges x 100 m = 7'500 metres. And spraying 0.2 m wide over each ridge then the total area treated for each field hectare is 7'500 metres x 0.2 m = 1'500 m² (Fifteen hundred square metres)

No formulas please. Taking a look at the spray- volume: it is specified in litres of spray-mix per treated hectare not the actual area to be treated for each field hectare. So the 120 litres has to be sprayed over 10'000 m² .

HOW MUCH SPRAY-VOLUME GOES DOWN ON EACH SQUARE METRE? READ THAT AGAIN. 120 litres per 10'000 m² or as pointed out elsewhere on this blog, per = for each. 120 / 10'000 = 0.012 litres/m²

I can just hear the moans and groans when some of you have to shift that decimal place. Repeat the calculation by converting the 120 litres into millilitres - 120'000 ml / 10000 m² = 12ml per square metre. 1'500 m² is being treated for every field hectare so the actual usage per field hectare - ha_f = 12ml x 1500 m² = 18'000 ml or 18 litres for each field hectare.

There is another way of looking at the situation but that's for the next posting.

Does this help in deciding which nozzle-tip to use? Not really because you need to know the flow rate in litres per minute.

chemicon@multispray.com

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