The 'Paddock Total' Tally (in the box in the lower left of the Task Screen) keeps track of the Ha and L used in that Paddock, to help manage what is left to do in the Paddock if it is only part sprayed.
When you come back into the paddock however for a new round of spraying later in the season, you need to Reset this Tally, otherwise it will continue adding to the Ha and L accumulated from the previous spray round.
To Rest the 'Paddock Total' Tap the white button next to Rest Paddock?
So to make full use of this Tally function, when you start a new round of spraying in a Paddock (as opposed to completing the current spray round), you should get into the habit of Resetting the Paddock when you start the first Task of this round. If you forget to reset, it has no effect on any other functions, other than that the Paddock Total and Paddock Remaining Tallies will not be of any use to you.