You can opt to spread in one pass or two overlapping passes at half the rate. Two passes is likely to give a better result. Either way you will need to calibrate the spreader accordingly.
The Ev-N-Spred 2050P spreader has a numerical scale, the setting is dependent on the granule size and density. The fertilisers that I supply are virtually all the same consistency so once you have calibrated the spreader you won't have to change it again. I use a setting of 10.5 on the scale provided. This delivers about 15 to 16 gsm and I always do a double pass so the toatal amount applied is 30 to 32 gsm.. You may need to make small adjustments because your walking speed may differ from mine.
For other spreaders you will need to calibrate the spreader. Here are two ways to calibrate - I have tried both but prefer the second - the lazy way!
The scientific way.
To calibrate you need a length of polythene or tarpaulin about 4 metres by 10 or 15 metres. A 10 metre tape measure. A set of hanging scales and bucket.
1/. Weigh 5kg of fertiliser into bucket.
2/, Pull lever on and walk at normal speed for 10 metres over polythene then immediately switch off.
3/. Tip remaining fertiliser from spreader into bucket and weigh to establish how much fertiliser has be used.
4/. Measure spread width.
5/. Calculate application rate: Weight used divided by area covered (Spread width x 10 metres). So if 500 grammes was used and the spread width was 10 metres the result would be 500 divided by 30 = 16.67 gsm. You want a rate of 16 gsm so adjust the lever setting accordingly. You can then re-run the test at the new setting. When you have finished you can retrieve the fertiliser from the polythene.
The lazy way
Weigh 5kg of fertiliser into a bucket and pour into the hopper. With a setting well below medium walk the spreader the length of one lawn and get an assistant to measure the spread width. Now calculate the area covered. This is 32 metres (the length of one lawn) x the spread width. If the spread width was 3 metres, the area covered is 32 x 3 = 96 sqm. Tip out the remaining fertiliser from the hopper into the bucket and weigh again to see how much was used. If 2kg was used the application rate was 2000 grammes divided by 96 sqm = 20.83 gsm. Adjust the setting on the spreader accordingly and repeat the process but move one spread width across the lawn so that you don't double dose the lawn. Very soon you will have arrived at the correct setting and shouldn't have to make further changes. You may end up with a slightly uneven application where you started but if you approach this with a cautious setting to begin with no harm will be done.
I find this is the easiest way and is more accurate than the scientific way because the area covered is so much larger.
Calibrating a Boom Sprayer
The rate of flow is dependent upon the nozzles and the pressure generated by the pump. Nozzles can be changed for different spray rates but it is important to use only the nozzle make and design supplied with the sprayer. The various spray rates available for that nozzle type are delineated by colour and rate charts are available online so that you can select alternatives.
Fill the tank with 50 litres of water. Then switch on the pump and time how long it takes to use up the 50 litres. The actual spraying distance to cover one croquet lawn with a 3 metre boom sprayer is about 306 metres and ideally you want to cover the area twice in overlapping bouts. So the total spray distance to be covered is 612 metres. If, in the test above, the sprayer delivered 50 litres in 10 minutes, you know that you need to travel at 61 metres per minute - which equates to nearly half a minute to cover the length of a croquet lawn. You can now check this out by spraying the lawn with clean water and adjust your speed accordingly. When actually spraying, I check after the first pass to see how much I have used and compensate for any error on the second pass.
To apply fertiliser accurately you should use bout markers. These can be anything from bamboo canes to flower pots. I use electric fence posts which have sharp spikes and are easy to use. They are available on E bay. At croquet clubs it is a good idea to have permanent bout markers, these can be painted on boundary boards (see the picture below). The markers are set one spread width apart - which is 3 metres for the spreaders and the boom sprayers that I supply. For the first pass start 3 metres from the boundary and travel up and down aiming between the markers ie from gap to gap. Then spread/spray the 3 metre wide strips at the North and South boundaries. For the second pass repeat the process but instead of going gap to gap, you go marker to marker thus overlapping the previous application. Spread/spray the 3 metre strips at the North and South and you will be left with two 1.5 metre strips down the East and West boundaries. Set the 2050P shut off lever so that it spreads half width and apply to those strips. The SCH sprayer has valves to enable half width spraying. The Enduramaxx has a valve which reduces the spray width to about 2 metres which is good enough for these edges.
The pictures below illustrate the first and second passes which overlap thus giving a uniform application. The photograph shows bout markers painted onto boundary boards. They are alternately 1 stripe then 2 stripes then 1 then 2 etc. The marks must be discernible from the far end of the lawn or lawns and the alternate stripes make it easy to select the correct target mark.
I hope this helps. If in doubt please let me know. DON'T leave the spreader lever open or the sprayer switched on when you stop - the fertiliser will keep flowing even when stationary.