Field crops may be classified in more than one way. It may be on the basis of:

1)Climate:
Tropical: Crops grow well in warm & hot climate. E.g. Rice, sugarcane, Jowar etc
Temperate: Crops grow well in cool climate. E.g. Wheat, Oats, Gram, Potato etc.

2) Growing Season:
Kharif/Rainy/Monsoon crops: The crops grown in monsoon months from June to Oct-Nov, Require warm, wet weather at major period of crop growth, also required short day length for flowering. E.g. Cotton, Rice, Jowar, bajara.
Rabi/winter/cold seasons crops: require winter season to grow well from Oct to March month. Crops grow well in cold and dry weather. Require longer day length for flowering. E.g. Wheat, gram, sunflower etc.
Summer/Zaid crops: crops grown in summer month from March to June. Require warm day weather for major growth period and longer ay length for flowering. E.g. Groundnuts, Watermelon, Pumpkins, Gourds.

3)Use/Agronomic classification:
Grain crops: may be cereals as millets cereals are the cultivated grasses grown for their edible starchy grains. The larger grain used as staple food is cereals. E.g. rice, Jowar, wheat, maize, barley, and millets are the small-grained cereals which are of minor importance as food. E.g. Bajara.
Pulse/legume crops: seeds of leguminous crops plant used as food. On splitting, they produced dal which is rich in protein. E.g. green gram, black gram, soybean, pea, cowpea etc.
Oilseeds crops: crop seeds are rich in fatty acids, are used to extract vegetable oil to meet various requirements. E.g. Groundnut, Mustard, Sunflower, Sesamum, linseed etc.
Forage Crop: It refers to vegetative matter fresh as preserved utilized as food for animals. Crop cultivated & used for fickler, hay, silage. Ex- sorghum, elephant grass, guinea grass, berseem & other pulse bajara etc.
Fiber crops: crown for fiber yield. Fiber may be obtained from seed. E.g. Cotton, steam, jute, Mesta, sun hemp, flax.
Roots crops: Roots are the economic produce in root crop. E.g. sweet, potato, sugar beet, carrot, turnip etc.
Tuber crop: crop whose edible portion is not a root but a short thickened underground stem. E.g. Potato, elephant, yam.
Sugar crops: the two important crops are sugarcane and sugar beet cultivated for production for sugar.
Starch crops: grown for the production of starch. E.g. tapioca, potato, sweet potato.
Dreg crop: used for preparation of medicines. E.g. tobacco, mint, pyrethrum.
Spices & condiments/spices crops: crop plants as their products are used to flavor taste and sometime color the fresh preserved food. E.g. ginger, garlic, chili, cumin onion, coriander, cardamom, pepper, turmeric etc.
Vegetable crops: may be leafy as fruity vegetables. E.g. Palak, mentha, Brinjal, tomato.
Green manure crop: grown and incorporated into soil to increase fertility of soil. E.g. sun hemp.
Medicinal & aromatic crops: Medicinal plants include cinchona, isabgoli, opium poppy, senna, belladonna, rauwolfra, iycorice and aromatic plants such as lemon grass, citronella grass, palmorsa, Japanese mint, peppermint, rose geranicem, jasmine, henna etc.

4) Life of crops/duration of crops:
Seasonal crops: A crop completes its life cycle in one season-Karin, Rabi. summer. E.g. rice, Jowar, wheat etc.
Two seasonal crops: crops complete its life in two seasons. E.g. Cotton, turmeric, ginger.
Annual crops: Crops require one full year to complete its life in a cycle. E.g. sugarcane.
Biennial crops: which grows in one year and flowers, fructifies & perishes the next year? E.g. Banana, Papaya.
Perennial crops: crops live for several years. E.g. Fruit crops, mango, guava etc.

5) Cultural method/water:
Rainfed: crops grow only on rainwater. E.g. Jowar, Bajara, Mung etc.
Irrigated crops: Crops grows with the help of irrigation water. E.g. Chili, sugarcane, Banana, papaya etc.

6) Root system:
Taproot system: The main root goes deep into the soil. E.g. Tur, Grape, Cotton etc.
Adventitious/Fiber rooted: The crops whose roots are fibrous shallow & spreading into the soil. E.g. Cereal crops, wheat, rice etc.

7) Economic Importance:
Cash crop: Grown for earning money. E.g. Sugarcane, cotton.
Food crops: Grown for raising food grain for the population and & fodder for cattle. E.g. Jowar, wheat, rice etc.

8) No. of Cotyledons:
Monocots or monocotyledons: Having one cotyledon in the seed.
Gramineae: includes the following crops: wheat, barley, rice, maize, oat, sugar cane, sorghum, ryegrass, and sudangrass.
Liliaceae: includes onion and garlic.

Dicots or dicotyledonous: Crops having two cotyledons in the seed.
Leguminosae: field bean, lupine, chickpea, lentil, fenugreek, Egyptian clover, alfalfa, soybean, peanut, grass pea, castor bean, red clover and white clover.
Malvaceae: cotton.
Linaceae: flax.
Solanceae: potato, tomato, and tobacco.
Pedaliaceae: sesame.
Composite: sunflower and safflower

9) Photosynthesis (Reduction of CO2/Dark reaction):
C3 plants: Photorespiration is high in these plants C3 Plants have lower water use efficiency. The initial product of C assimilation in the three ‘C’ compounds. The enzyme involved in the primary carboxylation is ribulose-1,-Bisphosphate carboxylase. E.g. Rice, soybeans, wheat, barley cotton, potato.
C4 plants: The primary product of C fixation is four carbon compounds which may be malice acid or acerbic acid. The enzymes responsible for carboxylation are phosphoenol Pyruvic acid carboxylase which has a high affinity for CO2 and capable of assimilation CO2 event at a lower concentration, photorespiration is negligible. Photosynthetic rates are higher in C4 than C3 plants for the same amount of stomatal opening. These are said to be drought resistant & they are able to grow better even under moisture stress. C4 plants translate photosynthates rapidly. E.g. Sorghum, Maize, Napier grass, sesame etc.
CAM plants (Crassulacean Acid Metabolism): the stomata open at night and a large amount of CO2 is fixed as a malic acid which is stored in vacuoles. During day stomata are closed. There is no possibility of CO2 entry. CO2 which is stored as malice acid is broken down & released as CO2. In these plants, there is negligible transpiration. C4 & CAM plants have high water use efficiency. These are highly drought resistant. E.g. Pineapple, sisal & agave.

10) Length of Photoperiod required for Floral Initiation:
Most plants are influenced by the relative length of the day & night, especially for floral initiation, the effect on a plant is known as photoperiodism depending on the length of photoperiod required for floral ignition, plants are classified as:
Short-day plants: Flower initiation takes plate when days are short less than ten hours. E.g. rice, Jowar, green gram, black gram etc.
Long day’s plants: require long days are more than ten hours for floral ignition. E.g. Wheat, Barley,
Day-neutral plants: Photoperiod does not have much influence for phase change for these plants. E.g. Cotton, sunflower. The rate of the flowering initiation depends on how short or long is photoperiod. Shorter the days, more rapid initiation of flowering in short days plants. Longer the days more rapid are the initiation of flowering in long days plan