Pre-conditions of agricultural development like land clearance was constrained by ecology and technology. The Gangetic plains were heavily forested and it was not before the effective use of iron began that the fertility of the soil could be tapped for agriculture on a wide scale.
Not all the regions within Northern plains were as fertile as the Gangetic area. Therefore complex societies could be sustained in the middle Gangetic plains and Eastern India. Here wet-rice cultivation yielded higher surplus. The rain-fed agriculture in the northwest was utilised to produce wheat and barley.
The drier areas normally practiced cattle breeding. Western Rajasthan, the region of Thar Desert, hardly permitted conditions of cultivation. Caravan traders frequented the desert and subsequently the trading centres grew in the region. However, with the development of irrigation facilities some of the sub- regions in Rajasthan began to be cultivated.
In contrast, the areas in the Northeast, Bengal and Orissa benefited from the blowing of the Northeast monsoon from December to February.
These areas received plenty of rain and were hence blessed with dense vegetation. Though it is difficult to map climatic changes and its consequences for agriculture but such changes have been indicated for the middle of the first millennium AD.
Analyses of plant remains and soil belonging to the post-Harappan period in the Northwest point to growing aridity. The variations in the settlement patterns and forests were often guided by climatic conditions. In the drier areas villages were generally nucleated.
Fields bounded the settlements and pastures were located far away. In the wetter, rice- growing eastern India linear homesteads were the norm. As far as forests are concerned, the range included extensive rain forests of the wetter areas to tropical deciduous to pine and fir.
Vegetation in these forests ranged from Savanna, bushes and coarse grasses to teak, ebony and sandalwood. The river systems of the Indus, the Ganges and the Mahanadi had estuaries where mangrove swamps could be found.
Soil types have been the other important factor, which has decided the agricultural viability of different regions. From the fertile alluvial and cotton soil to not so fertile red soil and laterite, the differentiated availability of natural nutrients, water retention and pliability have all determined the nature and rate of agricultural growth. Riverine regions, which silt the flood plain, are preferred even when the location is hazardous. In relatively elevated areas deep ploughing is required.
The use of ploughshare, iron in the north and wood in the peninsular region and its consequences for the agriculture has been debated among historians rather animatedly. Uncertainties and vagaries of climate made cultivators dependant on agricultural calendars prepared by the local brahmanas.
The agricultural operations of sowing and harvesting came to be associated with lunar and solar calculations. These calculations were based on the study of the phases of the moon, equinoxes and solstices.