It seems you are trying to compare different things: “balanced field length” with “over 50 ft”. Let's clarify:

*Balanced field length*: This is the way large commercial airplanes take off to ensure there is sufficient runway length to stop in case of aborted take-off. So there is a point beyond where the take-off must continue (expressed as *V1 speed*). From Wikipedia, [balanced field takeoff][1]:

> The accelerate-stop distance required (ASDR) is equal to the takeoff
> distance required (TODR) for the aircraft weight, engine thrust,
> aircraft configuration and runway condition.

*Over 50 ft*: This is the distance from the start of the ground roll to the point where the aircraft is airborne and 50 ft over the runway, to ensure obstacle clearance. 35 ft is another typical obstacle clearance in the US, and indeed the distance to climb to 35 ft is shorter than the previous one.

**Using the diagram**

From [this slideshow][2] which reproduces the figure you refer to:

[![enter image description here][5]][5]  
([Source][2])

This gives the distances for the take-off, either the ground roll distance or the obstacle clearance distance (35 and 50 ft), but not all are available for each type of aircraft (propeller or jet).

There are 3 groups from left to right:

 - Jet using balanced field T/O (the obstacle clearance is implicitly 35 ft).
 - Jet not using balanced field T/O.
 - Propeller (not using balanced field T/O).

In these groups, there are one or two data provided:

 - Jet using *balanced field T/O*. The only distance provided is the the T/O distance with 35 ft obstacle clearance. You must choose the right curve, depending on the number of engines (*twin*, *tri* or *four-engine*).

 - *Jet* / *propeller* not using balanced field T/O. There are two data provided and you may need both. *Ground roll* is the distance until the aircraft leaves the ground (liftoff); *50 ft* is the ground roll + the distance to climb to 50 ft.

See also: [What would be the ground roll and total distance to clear a 50ft obstacle given these conditions?][3]

  [1]: https://en.wikipedia.org/wiki/Balanced_field_takeoff
  [2]: http://stl-www.aero.kyushu-u.ac.jp/member/tani/tokuron/2014Lecture/CD201404_DesignProcess_configuration.pdf
  [3]: http://aviation.stackexchange.com/questions/5060/what-would-be-the-ground-roll-and-total-distance-to-clear-a-50ft-obstacle-given
  [4]: http://fsims.faa.gov/wdocs/8900.1/V04%20AC%20Equip%20&%20Auth/Chapter%2003/04_003_002.htm
  [5]: https://i.sstatic.net/nCWhJ.png