As a EU citizen you do not need a work permission. BUT you must pay attention to special regulations in agriculture.
In Germany, every employee and employer must pay social security contributions. (health Insurance, pensions, unemployment insurance). The exception is you work less than 70 days. Then you are a short-time worker.
You can only work short-time in Germany, if the short-term work is not your main occupation. That means you must have a job or be self-employed in your country of origin. Note: short-time employment is also possible for homekeepers.
Students can work short-time in agriculture during holidays and semester breaks.
You want to work in agriculture in Germany less than 70 days (short-time). You have to prove your employer you are socially insured in your country of origin, for example with the A1/E101 form. Ask your National Social Insurance Institution (PL: ZUS) for A1/E101 form.
Remember, as a short-time worker you are NOT health-insured (except accidents) in Germany.
The A1/E101 form guarantees that you still have health insurance in your home country. You can find the A1 form here.
You want to work longer than 70 days
You want to work in agriculture in Germany for more than 70 days or as your main occupation, please keep in mind that your employer must register you as a regular employee in German agricultural in the German Social Insurance System.
Learn more about Social Insurance