Zynga Serve Rewards, the program will reward players with Farm Cash for buying stuff using a special Zynga Serve Rewards card attached to a debit or credit account anywhere American Express is accepted.

All interested players need to do is register for the Zynga Serve Rewards card online, which they'll receive in the mail. Before signing up through American Express, though, they'll need to plant a special Serve Money Tree on their digital farm land. Then, players will have to add a bank account, credit card, debit card, or cash with a GreenDot MoneyPak to the card.

After finally activating the card, the first five purchases that players make either in stores or online that are $25 or more will net them a bonus 50 Farm Cash. Eventually, Zynga and American plan to open the account to more of Zynga's games and offer more than just virtual currency, like in-game items and boosts.

The service will also offer a more one-to-one reward system for purchases made using the card in the future. This is an interesting way for Zynga to get its players to pay up, but we wonder exactly how much Zynga looks to make with this initiative, considering both American Express and Facebook are likely taking cuts from the top. Regardless, a move like this could potentially make a social gaming sea filled with plenty more whales.