function sowed(address farmer) constant public returns (uint256 balance) {
        var list = fields[farmer];
        for (uint i = empties[farmer]; i < list.length; i++) {
            
            var elapsed = block.timestamp - list[i].sowed;
            if (elapsed >= growth) {
                continue;
            }
            
            balance += list[i].potatoes + list[i].potatoes * elapsed / growth;
        }
        return balance;
    }