Agricultural income computation affects income tax liability by aggregating incomes, computing tax on totals, then subtracting adjusted agricultural tax. Income-tax for the assessment year beginning 1 April 1998 is charged at rates in the First Schedule, subject to special computation where an assessee has net agricultural income above the prescribed threshold: aggregate total and agricultural income, compute tax on the aggregate, compute tax on agricultural income after adding a base amount at the same rates, and deduct the latter from the former to determine tax on total income; analogous procedures apply to advance tax and tax for other specified periods or provisions.