AGR 201 Principles of Agronomy Notes PDF

**AGR 201: PRINCIPLES OF AGRONOMY** **[ORIGIN AND CLASSIFICATION OF CROP PLANTS]** **[Origin of cultivated crop plants]**: all basic cultivated crop plants in Nigeria are believed to have been derived from wild species after a series of breeding programmes and domestication. However the history of...

**AGR 201: PRINCIPLES OF AGRONOMY** **[ORIGIN AND CLASSIFICATION OF CROP PLANTS]** **[Origin of cultivated crop plants]**: all basic cultivated crop plants in Nigeria are believed to have been derived from wild species after a series of breeding programmes and domestication. However the history of many of these crops is highly speculative. Notwithstanding, all the widely cultivated crop species are adopted to the need of the cultivators and the consumers. The centers of origin of cultivated crop plants were found to be in areas favoured by a more or less equiable climate. This shows that right from center of origin of most crop species climatic conditions have been very importantly influential.Vavilov (1926) predicted the center of origin of a crop by finding the region were the greatest diversity of type occurred in each crop plants. According to dictionary definition, diversity the state of being diverse and diverse is of different kinds. For instance, the area of different kinds of maize is the center of origin. However, more than one-type of crop appear to have originated in two or more centers or over wide ecological zones. In 1959, De Candolle concluded that 199 crops (81.56%) originated in the old world, and 45 crops (18.44%) in the new world (Americas). The crop plants peculiar to the western hemisphere include maize, cocoa, potato, sweet potato, groundnut, rubber, tobacco, etc. Eurasia (Europe and Asia) produce wheat, barley, rye, rice, peas, soybean, sugar beets, sugar cane and most of the cultivated forage grasses and legumes. Citrus originated in South East Asia. Yams, sorghum, oil palm, coffee, cowpea, millet, etc were domesticated in Africa. Cotton originated in both new and old worlds. Most cultivated crop plants have undergone extensive breeding modifications from their wide prototypes as result man's continuous efforts to improve or domesticate them. The differences between wild and cultivated crops species are largely in their increased usefulness to man and livestock, such usefulness has yield, quality, etc. in other words, it is those crops species that are useful to man and his livestock that are widely cultivated the world over. Such selected cultivated crop species had been distributed widely from one nation to the other year in year out through several agents and methods. The spread of cultivated crop plants has been very important in the diversification of crop production techniques and in the production of new crop varieties. In their migrations, in various forms, people invariably have taken their basic cultivated plants with them to insure a permanent food supply and support their sociocultural set up. This actually happened mainly during the slave trade. Cocoa has been recorded to be introduced to Nigeria by the Portuguese from Americas. Similarly most African crops were taken to the new world and Eurasia. Man also transported weeds, diseases and pests along with the crops. This is the pasture of crop distribution in the world. **[Classification of Crop Plants]**: crop plants may be classified on the basis of a morphological similarity of plant parts. This would be botanical classification and this has been discussed in introductory plant biology. Briefly crop plants belong to the spermatophyte division of the plant kingdom in which reproduction is carried on by seeds. Within this division, the common crop plants belong to the subdivision of angiosperms, which are characterized by having their ovules enclosed in a bag called ovary. The angiosperms in turn are dived into two classes, the monocotyledons and the dicotyledons. All the grasses including the cereals and sugarcane are monocotyledonous plants. The legumes and other crop plants are classified as dicotyledonous plant. These classes are subdivided into orders, families, genera, species, subspecies and varieties. Crop may also be classified agronomically according to use of disposition. Farmers choose their crops on the basis of agronomic rather than botanic classification. According to use, crop plants may be classified into field crops, horticultural crops, forests and weeds. Field crops include all cultivated crop plants grown under a relatively extensive system of culture. Horticultural crops include fruits, nuts, floricultural crops and vegetable crops. One of the unique differences between field crops and horticultural crops is that the latter require less preparation or processing before consumption. A ripe mango fruit, or a ripe orange fruit, or tomato fruit, doesnot require much, preparation before is due for eating. This is quite unlike yams, cassava, maize, or cowpea. Forest and range species are primarily native plants used for grazing livestock or for timber production. A weed is any plant growing where it is not wanted. Field crops consist of arable crops and tree crops. They are annuals, biennials, or perennials. Arable crops widely grown in Nigeria include maize, rice, sorghum, millet, yams, cassava, sweet potato, cocoyams,cowpea, pigeon pea, groundnut, soybean, lima bean, vegetables of different types, cotton, kenaf, sisal, tobacco, sugarcane, etc. Also permanent tree crops that are grown widely in Nigeria include cocoa, kola, rubber, oil palm, citrus, cashew, coffee, plantain, etc. Agronomically, on the basis of disposition field crops are classified into the following categories: **[Grain crops]**: these are grain producing crops which include cereals, the large-seeded legumes, and some other species. Many people refer to the cereals as the only grain crops. This believe is not always very distinct, rather it is a believe of misconception of collective term applied to cereals. Cereal crops include wheat, oats, barley, rye, rice, maize, sorghum, millets, etc. while the large-seeded legumes include groundnut, beans, soybeans, cowpeas, lima bean, pigeonpea, etc. Rice, maize, sorghum, millet, groundnut, cowpea, pigeon pea are widely cultivated in Nigeria. **[Forage crops]**: These are crops grown for vegetable matter or vegetative part. They are fresh or preserved and utilized as feeds for animals. They are use forhay, silage, soilage, pasture, or fodder. Forage crops include grasses, legumes and other cultivated crops use as feeds for livestock. **[Fibre crops]**: These are crops grown for their future production. They include jute, cotton, flax, kenaf, sunnhemp; sisal, etc. cotton, kenaf and sisal are plentiful and importantly grown in Nigeria. **[Tuber crops]:** These include crops that are grown for their enlarged roots, stems and leaves. Tuber crops that enlarged their roots include cassava, carrot, sweet potato, sugar beets, etc. while yams are typical examples of crops that enlarged their system. Cassava and yams are important tuber crops extensively grown in Nigeria. **[Oil crops]**: these are crops grown for their oil. The oil crops include groundnut, sunflower, castorbean, oil palm, cottonplant, melon etc. **[Sugar crops]**: They include sugarbeet and sugarcane grown for their sweet juice from which sucrose is extracted. The only important sugar crop widely grown in this country is the sugarcane. **[Drug crops]**: plants from which chemicals can be extracted are collectively called drug crops. Drug crops include tobacco, coffee, tea and onion. Other drug crops are marijuana or hemp and a large number of weeds. **[Vegetable crops]**: These include potatoes, cabbages, carrots, onions, okra, pepper, leafy vegetable, such as amaranthus, celosia, cochorus, etc. Vegetable crops are grown for their vegetative parts, fruits or pulses chiefly as food for man and animals. **[Arable crops]**: These are crops grown mainly for human consumption. They are mainly annuals, but a few ones are biennials. They require extensive seedbed preparation. **[Permanent Crops]**: These are mainly tree crops such as cocoa, kola,rubber, etc. Many called them cash crops because they are mainly grown formoney fetching. Any field crop can be a cash crop. Permanent tree crops are all perennials. There are other frequently used methods of classifying farm crops.Crops may be classifiedinto three categories according to their effect on the soil; Crops may be classified soil-depleting such as the cereals, soil conserving or soil-building crops such as the legumes. Classification can also be made on the basis of disposition of the harvested crop. This may be termed special purpose classification. **[Cover Crops]**: Crops grown for the purpose of protecting bare soil from erosion are called cover crops and if they are ploughed under to increase the organic matter content of the soil they are called green manure crops. **[Cash Crops]**: They are set of crops grown mainly for exchange for money. It could be arable or permanent tree crops. **[Catch Crops]**: These are crops planted late as substitutes after the regular crops have failed. Short season crops are generally used as substitute crops for regular long season crops. **[SoilingCrops]**: These are set of crops out and fed green to livestock, such as legumes and grasses. **[Silage crops]**: silage crops include forage legumes and grasses. They arepreserved in a succulent condition by partial fermentation in an air tight receptacle or silo. **[Trap crops]**: These are crops grown to attract insect or parasites and later destroyed or ploughed under once they have served their good purpose. **[Companion Crops]**: These are sometimes called nurse crops. CompanionCrops Such as cocoyam, Cassava, maize, yam, etc. are grown with crops like cocoa, kola, coffee, oil palm, etc in order to secure a return from the land in the first two to three years ofcultivation. In this country, farmers usually plant arable crops with seedlings of tree crops with the hope of providing shade to the seedlings and a return. This is another form of multiple cropping systems.