Agriculture in the Indus Valley Civilization
Even though, the nature of the Indus civilization's agricultural system is still largely a matter of conjecture due to the paucity of information surviving through the ages, the possibility of speculation remains.
Historians believe that the Indus Valley civilization agriculture must have been highly productive; after all, it was capable of generating surpluses sufficient to support tens of thousands of urban residents who were not primarily engaged in agriculture. It relied on the considerable technological achievements of the pre-Harappan culture, including the plough. Still, very little is known about the farmers who supported the cities or their agricultural methods. Some of them undoubtedly made use of the fertile alluvial soil left by rivers after the flood season, but this simple method of agriculture is not thought to be productive enough to support cities. There is no evidence of irrigation, but such evidence could have been obliterated by repeated, catastrophic floods.
The Indus Valley civilization appears to contradict the hydraulic despotism hypothesis of the origin of urban civilization and the state. According to this hypothesis

cities could not have arisen without irrigation systems capable of generating massive agricultural surpluses. To build these systems, a despotic, centralized state emerged that was capable of suppressing the social status of thousands of people and harnessing their labor as slaves. It is very difficult to square this hypothesis with what is known about the Indus civilization. There is no evidence of kings, slaves, or forced mobilization of labor.