Plot marking in field trials: What is the best way setting out right angles and perpendicular lines?
The answer depends on multiple factors. How many hands are there in the field? What equipment is available? And what is the topography of the field?
Being generally the only person setting up the trials, I find the best way is to use the 3-4-5 method. For those who are lucky enough to deploy three people, the method is crudely explained by FAO. But what if you are the only one out there? Read on.
To set out right angles in the field, you need a measuring tape (longer the better), rope, pegs, and a little bit of love for basic geometry. Below is the description leading to form a 3m x 5m single trial plot. It can be extended to 6m-8m-10m, 9m-12m-15m etc.
After determining where in the field your trial is going to take place;
1) Drive in a peg into the soil where you think the corner of the first trial plot would be. This is your peg #1 (Fig 1). Tie a rope around it, measure 3m towards a direction which will form the 3m side of the plot, and drive in another peg at the 3m mark while stretching the rope. This is your peg #2. Make a loop around it.
2) Approximately perpendicular to #2, measure 4m and drive in the 3rd peg into the soil while keeping the rope stretched. Make a loop around #3 as well.
By now, you have three pegs in the soil (Fig 1). More importantly, 5m more to measure, which is the hypotenuse (diagonal bit) of the 3-4-5 triangle.
3) Simply measure 5m from #3 towards the #1, and then link the 5m mark and #1 (Fig 2). If necessary, change the place of #1 while maintaining the 3m distance between #1 and #2.
The angle between 3m and 4m sides is now exactly 90°. Happy trials!