Punjab ranked first in GDP per capita amongst Indian states in 1981 and fourth in 2001, but has experienced slower growth than the rest of India, having the second-slowest GDP per capita growth rate of all Indian states and UTs between 2000 and 2010, behind only Manipur.[78][79][80][81][82][83][84] Punjab's economy has been primarily agriculture-based since the Green Revolution due to the presence of abundant water sources and fertile soils;[85] most of the state lies in a fertile alluvial plain with many rivers and an extensive irrigation canal system.[62] The largest cultivated crop is wheat.