Bihar lies in the river plains of the basin of the river Ganga. It is endowed with fertile alluvial soil with abundant water resources, especially ground water resources. This makes the agriculture of Bihar rich and diverse. Rice, wheat, and maize are the major cereal crops. Arhar, urad, moong, gram, pea, lentils, and khesaria are some of the pulses cultivated in Bihar. Bihar is the largest producer of vegetables, which is dominated by potato, onion, eggplant, and cauliflower. In fruit cultivation, it is the largest producer of lychee and the third largest producer of pineapple, as well as a major producer of mango, banana, and guava. Sugar cane and jute are two other major cash crops of Bihar.

The average rainfall in Bihar is 1053 mm. The rainfall in Bihar is largely due to the south-west monsoon, which accounts for around 85% of total rainfall in the state. The other sources (winter rain, hot-weather rain, and the north-west monsoon) account for the remaining 15%. The average normal rainfall in the state is more or less adequate for its agricultural operations. However, year-to-year changes lead to drought or flood, causing extensive damage to the crop production and the overall income of the state.

Bihar has a geographical area of 9,360,000 hectares with three important agro-climatic zones: North-West, North-East, and South. The North-West zone has 13 districts and receives an annual rainfall of 1040–1450 mm. The soil is mostly loam and sandy loam. The North-East Zone has 8 districts; it receives rainfall ranging from 1200–1700 mm, and has loam and clay loam soils. Finally, the South Zone (17 districts) receives an average annual rainfall of 990–1300 mm. Its soil is sandy loam, loam, clay, and clay loam.

The net sown area in Bihar is 60% of its geographical area. This percentage is much higher than the all-India average of 42%. Such a high percentage of cultivated land is possible for two reasons. First, most of Bihar is plain area suitable for agriculture. Second, most of the forest had been converted into farmland during the last 2000 years. Currently, land under forest constitutes only 6% of the area.

Rice is cultivated in all districts of Bihar. Autumn rice, aghani rice, and summer rice are three different varieties of rice grown at three different times of the year. The average production of rice is around 5 million tonnes each year. Some five decades back, wheat cultivation was very restricted in Bihar. After green revolution success, wheat was planted by Bihari farmers on a larger scale, and wheat now occupies the status of major crop of the rabi (spring) season. The average annual wheat production is approximately 4-4.5 million tonnes. Maize is also cultivated, with an average annual production level of approximately 1.5 million tonnes and a steady positive trend in production. The leading producer districts are Khagaria and Saharsa. Pulses such as moong, arhar, peas, and khesari are grown, more in southern than in northern Bihar. The leading districts are Patna, Bhojpur, Aurangabad, and Nalanda.

The total area under vegetable cultivation is currently about 11% of the state’s gross sown area, and is increasing. The important vegetable crops include potato, onion, tomato, cauliflower, and brinjal. Hajipur in Vaishali is famous for an early variety of cauliflower that reaches market in the last week of September. Production of vegetables is well dispersed over the districts, with a concentration of production in some particular districts. Apart from Patna and Nalanda[Jehanabad] , where vegetable production is quite extensive, the other districts with high shares in total vegetable production are Vaishali, Muzaffarpur, West Champaran, East Champaran, Katihar, and Begusarai.