Zakat on ushar

The person who gets 28mounds and 5 kilograms agricultural foods on his hand , must pay ushar or 1/10 food as per zakat. The  lands which become cultiable through natural way that means by rain, water of drain,river,fountain , then only that lands ushar or zakat will be 1/10. On the other hand,those lands which are cultiable through artificial way such are using beast, machinery,labour then that lands zakat will be 1/20.