You can get some people to help you out on the farm. It cost quite a lot of money to employ someone so it is advised to not employ anyone when you just started the game. When you find that your main farmer does not have enough endurance to do his job and that your income per turn is more than 50$ you should consider having an employee. To be able to employ employees, your farm has to be on Amateur level and your house size has to be upgraded.
To employ someone, go to the Staff interface, click on Recruit and select the appropriate employee. Employees, like your farmer has skill levels, the higher the skills the better they will perform. Skills will gain levels just by using the appropriate actions. For example, if an employee tills the land often, his tilling skill will get better. With higher skills the employee will use less endurance so you might consider specializing your farmer and employees for certain types of tasks. When you have chosen an employee, click on Hire.
To select an employee and to use his endurance instead of your main farmer's, click on his name on the main interface. After clicking your main farmer endurance bar will be replaced by your employee's. From now onwards, every task done in your farm will use your employee's endurance. To switch back to your main farmer, just click on his name. You can even use your number keys (key 1,2,3...) to browse through your employees. Note that on most actions an employee or your main farmer will be highlighted, this means his skills are more adapted for the task, you ought to select the highlighted employee to do the task.
An employee cost money so you must be sure to pay him every four turns. An unpaid employee will leave your farm and you will loose a lot of fame (-10% total fame and -10 fame). If you can't afford the employee you will have to fire ... but note that firing an employee will cost you money (4 turns of salary) but you will not loose fame.