What is the definition of crop?

Plants planted directly or indirectly to meet human needs. The word "crop" is borrowed from Japanese, but it is called "valley" or "valley" in China ancient books. In ancient times, there were so-called "five grains", "six grains", "nine grains" and even "hundred grains", in which the meaning of grain was constantly developing, from rice, millet, wheat, glutinous rice to hemp, fruits, vegetables and even all cultivated plants. The word "crop" has been quoted in China agricultural literature since the beginning of the 20th century, and now it is popular, commonly known as "crop".

There are more than 2,000 kinds of plants cultivated and utilized by human beings, but now there are only more than 30 kinds of crops cultivated in a large area. Other kinds of vegetables, melons and fruits, ornamental plants, and sometimes fruit trees in woody plants are usually cultivated in a small area, which is called horticultural crops. With the development of human demand, in addition to traditional crops, there are more and more plants that can be used as food, beverage, medicine and various industrial raw materials, and most of them have been included in the category of crops. Although all kinds of forage grass and green manure can't be eaten directly by human beings, they are mostly cultivated crops now, because they are very important for the development of animal husbandry and planting.

The origin and spread of wild plants have been domesticated and cultivated into crops about 10000 years ago. After long-term conscious or unconscious selection and isolation, the plant species originally cultivated and utilized by human beings have formed many varieties and types that are more suitable for human needs than the original species. For example, cultivated rice, millet, corn and cultivated soybean are quite different in appearance and practical value compared with their wild ancestors such as wild rice, Setaria viridis, Mexican corn and wild soybean, and taxonomists have also divided them into two different species. But in fact, their genetic relationship is very close, the number of chromosomes and even the genome are the same, and it is easy to bear fruit by crossing with each other. But the former has been cultivated and selected by human beings, and the latter is still in the wild. Of course, the existing cultivated varieties also have different forms. For example, two types of flax, fiber and oil, are distinguished from wild gray flax by artificial selection; Sunflower may be a hybrid of various wild sunflowers. Humans domesticated some crops by using naturally occurring allopolyploids. For example, the common wheat with the largest cultivated area in the world is a hexaploid synthesized from three diploid wheat (or Aegilops tauschii); Upland cotton is also an allotetraploid naturally synthesized from Asian cotton or grass cotton and Peruvian cotton. Various crops have different sources and forms, but they are not fully understood so far.

Botanists have different views on the geographical position and spreading process of cultivated crops in the world. It is generally believed that there are 12 kinds of crop diversity centers in the world, and each crop originated from one or several centers, or the secondary origin center generated by the primary origin center (see the theory of crop origin center). From the origin center, crops spread outward due to various factors. In addition to natural reasons such as water power and wind power, the rise of ancient cultural centers such as China, Egypt, Greece, Rome and Persia and the expansion of their influence, trade exchanges between different regions, wars and ethnic migration have accelerated the mutual spread of different crops produced in different places. The development of modern transportation and international economic exchanges has especially increased the opportunities for the spread of crops. Columbus arrived in America in the15th century, which played an important role in ending the long-term isolation between the old and new continents, communicating with various crop species and changing the face of world agricultural production. Nowadays, many crops with important economic significance have spread to places that can be planted all over the world, and new production centers have been formed, which are far from their original producing areas.

Due to the long-term adaptation to the natural environment of origin, distributed crops have certain requirements on temperature, light energy, moisture and other conditions during cultivation, which restricts the distribution of crops in different parts of the world.

According to the temperature conditions, four different temperature zones in the world have their own crops. ① Cold temperate zone. There are spring wheat, spring barley, spring oats, rye, millet, millet, potato, pea, broad bean, flax, beet and so on. ② Temperate zone. There are winter wheat, winter barley, millet, sorghum, soybean, broad bean, kidney bean, rape, sunflower, hemp and so on; ③ Subtropical. There are rice, corn, sorghum, sweet potato, soybean, kidney bean, rape, peanut, sesame, tung tree, mulberry, tea, cotton, jute, kenaf, ramie and so on. 4 tropical. There are rice, sweet potatoes, cassava, peanuts, island cotton, coffee, cocoa, rubber trees, oil palm, jute and so on. But this adaptability is not absolute. Some crops can also change their properties through natural or artificial selection because of the variation of genetic basis. For example, rice, corn and sorghum are originally warm crops. After growing in high latitudes for many years, they can produce varieties with short growth period and strong cold tolerance, which can be cultivated at 50 north latitude and 40 south latitude. Some varieties of sweet potato, cotton and ramie can also be introduced to 40 north latitude, and cassava can be introduced to 25 north latitude. At the same time, some crops originally suitable for cold temperate zones, such as wheat, can also be planted in low latitudes or high altitudes in winter. However, the range of crop adaptability change should not exceed a certain limit, otherwise it will grow poorly or fail to survive.

Judging from the response of crop growth and development to photoperiod, it can be roughly divided into two types: long-day crops and short-day crops. The former needs longer illumination time every day at a certain stage of the growth period, and generally needs more illumination time than no illumination time to complete reproductive growth and form flower buds. Insufficient light time slows down reproductive growth and delays flowering and fruiting; Instead, it can promote reproductive growth. Most of these crops are wheat, flax, sugar beet, potato, etc., which are suitable for growth in the north. In a certain stage of short-day crop growth, the dark time every day must exceed the sunny time to form flower buds, and the extension of dark time can promote reproductive growth; However, the extension of light time can only promote nutritional growth. Some spring-sown and autumn-harvested crops, such as rice, corn, sorghum, soybeans and hemp, fall into this category. The specific lighting conditions required by various crops also limit their adaptation and distribution. Due to long-term planting in different places, some crops have also differentiated into some early-maturing varieties that are insensitive to light. As for some crops with short growth period, such as buckwheat, mung bean and kidney bean. Their response to photoperiod is generally slow, and they can mature in any area as long as the temperature allows, so they belong to light-neutral crops.

Different crops have different drought tolerance, which can generally be expressed by transpiration coefficient, which is a sign of transpiration. Crops with low transpiration coefficient, such as millet, millet, sorghum, corn, barley, rye, peanut, sunflower, etc. , generally drought-tolerant; Crops with high transpiration coefficient, such as Coix lachryma, oat, buckwheat, soybean, broad bean, pea, rape and jute, have poor drought tolerance. Some crops, such as rice, are not only wet, but also their roots can be immersed in water without hindering their growth. As for wheat, potato, sweet potato, sugarcane, beet, sesame and cotton, they belong to "dry and wet intermediate crops".

In addition, the different sensitivity of crops to soil acidity and alkalinity is also related to their distribution areas. Generally, sorghum, Sudan grass, sesbania, alfalfa, sunflower, beet and so on. More salt and alkali tolerant; Rice, oats, rye, buckwheat, potatoes, sweet potatoes and tea are more acid-resistant. Most crops are suitable for neutral soil.

Life Cycle Crops have different life cycles. General herbaceous crops, from sowing and germination in spring to mature harvest in autumn, whose whole life cycle is completed within one year, are called "annual crops". Some crops, such as winter wheat and winter barley, are called "overwintering annual crops" or "perennial crops" if they need to be sown in autumn and mature from low temperature winter to the following summer. Some crops, such as beet, spinach, Chinese cabbage, radish, etc. That is, after sowing in 1 year, the vegetative growth in that year is completed, and it takes a winter to blossom and bear fruit in the next year, which is called "biennial crop". There are also "perennial crops" such as ramie, alfalfa, sugarcane, pyrethrum, pineapple, etc., whose life cycle is as long as more than 3 years. Besides harvesting the aboveground parts every year, the underground roots or rhizomes can grow continuously, which can be used for asexual reproduction and mostly grow in subtropical or tropical areas. Some crops, such as cotton and castor, are annual crops in temperate zone and can become perennial crops in tropical zone. As for woody plants such as tea trees, mulberry trees and fruit trees, they are all perennial crops.

There are two kinds of reproduction: sexual reproduction and asexual reproduction: ① sexual reproduction. Refers to the flowering and fruiting of crops, which are passed on from seed to seed. Among them, some crops can be self-pollinated, that is, pistils and stamens are in the same flower, and the outcrossing rate is about 1 ~ 5%. If it reaches 10 ~ 15%, it is a conventional outcrossing crop. Some are cross-pollinated. Androgyny or hermaphroditism, but the pistil and stamen are not on the same flower; The same flower also has male and female stamens, but due to the limitations of morphology, time and physiology, self-pollination is difficult, and it needs wind and insect vectors. These crops are outcrossing crops (see pollination and fertilization). ② Asexual reproduction. Reproduction by using plant organs. Tubers, tubers, rhizomes, bulbs, bulbs and aerial stems are all asexual propagators. Propagation methods include cutting, layering, rameting and grafting.

There are different classification methods for classified crops, and the classification based on use and botany is commonly used in agriculture (for the classification of horticultural crops, see vegetables and vegetable production, fruit trees and fruit production. Field crops can usually be divided into three categories according to their uses: edible, industrial raw materials and feed; Each category is subdivided into several subcategories. However, because the same crop often has multiple uses, it is generally only divided according to its main uses.

Cereal crops are also called food crops. For the purpose of harvesting mature fruits, it has become a basic food for human beings through processing procedures such as hulling and grinding. Most of them belong to Gramineae, such as rice, wheat, corn, sorghum, millet, coix lacryma-jobi and so on. However, buckwheat of Polygonaceae, quinoa of Chenopodiaceae and amaranth of Amaranthaceae are usually classified as cereal crops, or called fake cereals, because their uses are similar to those of Gramineae food crops. Generally, the seeds of cereal crops contain more than 70% starch, about 65,438+00% protein, and proper amount of fat and vitamins, which are the main sources of calories in food. Moreover, because of their easy planting, transportation and storage, they are the earliest domesticated crops in history and the largest cultivated crops at present. From 1982 to 1984, the cultivated area of cereal crops in the world reached more than 700 million hectares, accounting for 52% of the total cultivated area. Grain crops are mainly used as grain, and the seeds and bran screened during crushing can be used as concentrated feed; Straw can be used as coarse feed after crushing, and fresh stems and leaves can be used as green feed or silage. Fruit can also be used to make wine, and barley malt can be used to make caramel. Some seeds and germ are rich in fat, and the separated corn germ and rice bran can extract high-quality edible oil. The stems and leaves of rice, wheat and corn can also be used to compile various daily necessities and handicrafts.

Leguminous crops belong to Leguminosae. A crop whose purpose is to harvest mature seeds. There are mainly soybeans, peanuts, broad beans, peas, kidney beans, chickpeas, mung beans, Mi Dou, beans and so on. China is one of the countries with the richest bean cultivation. The protein content of mature seeds of legumes is higher than that of other crops, such as soybean, which can reach 40%, and other beans are all around 20 ~ 30%, which is 2 ~ 4 times of the protein content of cereals. Protein contains 8 kinds of amino acids necessary for animals. Lysine, arginine, valine and isoleucine, which are rare in cereal seeds, are rich in beans and can be directly eaten or processed into various bean products. The seeds of soybean and peanut are rich in fat, which is an important source of plant fat needed by human beings. The stems and leaves of beans have high nutritional value whether used as dry feed or green feed. Soybean cake or coarse powder produced by squeezing soybean and peanut oil can be used as concentrated feed and refined into concentrated protein. In addition, rhizobia symbiotic with leguminous crops can fix free nitrogen in the air, and the conical root system of leguminous crops is better than cereal crops in absorbing nutrients and water in deep soil, so planting leguminous crops or intercropping with cereal crops can also make full use of and cultivate soil fertility.

Potato crop is a kind of crop aimed at harvesting swollen roots, bulbs or tubers rich in starch and other polysaccharides. There are sweet potato of convolvulaceae, potato of Solanaceae, cassava of Euphorbiaceae, potato taro of Araceae, yam and potato, taro of Araceae, purple taro and konjac, Jerusalem artichoke of Compositae, bean potato of Leguminosae, banana lotus root of Cannaceae, etc. The underground rhizomes of these crops are swollen and consist of parenchyma cells, which mainly store starch, including about 2% protein and some vitamins. Except sweet potato is propagated by seeds, others are propagated by roots. Strong resistance to stress and insects, easy cultivation and high yield. Because potassium can promote the synthesis and accumulation of starch, it is often beneficial to increase production to pay attention to the coordination of potassium in the three elements when fertilizing. Potatoes are not only used as food and feed, but also as raw materials for starch, glucose, dextrin, synthetic rubber and alcohol in industry. Stems and leaves and processed powder residue are nutritious feeds. Fresh potato chips generally contain about 80% water, so transportation and storage are limited, so they need to be sliced and dried in the sun in time after harvest.

Fiber crops are a kind of crops whose main purpose is to harvest fiber. According to the tissues and organs that make up the fiber, it can be divided into: ① seed fiber. For example, the fiber system of cotton in Malvaceae is formed by the extension of epidermal cells of ovules, which is the most important textile raw material. ② bast fiber. For example, the fibers of all kinds of hemp are formed by the tough cortex of the stem. Among them, ramie of Urticaceae, flax of Lineaceae and Apocynum venetum of Apocynaceae have long and neat fibers, soft texture and little lignin, which can be used for spinning fine linen fabrics. Cannabis of the genus Cannabis, Jute of the genus Gastrodia, Abutilon of Malvaceae, Kenaf of Leguminosae, etc. Most of them are used to make burlap, sacks, carpets, hemp ropes, etc. Because of their poor spinnability. ③ Leaf fiber. Most of them are tropical monocotyledonous plants, such as sisal, agave, banana and pineapple. The vascular bundle fibers in leaf sheaths or leaves are thick and hard, which can not be used for textile, but have strong tensile force, moisture resistance, salt resistance and wear resistance, and can be used for weaving all kinds of thick ropes, which are widely used in navigation, mining and railway transportation. Palm of Palmae can be used as cushion, brush and hemp fiber. Others, such as Cyperaceae, Cyperaceae, Potamogeton, Juncus, Gramineae, Phragmites, Achnatherum, etc. , can also be used for knitting. All the above fibers can also be used as raw materials for papermaking. ④ Wood fiber. Mainly from woody crops, it is usually used to make high-quality paper.

Oil crops are a kind of crops aimed at harvesting oily organs and extracting oil. Besides peanuts and soybeans, leguminous crops also include rape, mustard, radish, sesame, sunflower and safflower in Compositae, flax, perilla and perilla in Labiatae and castor in Euphorbiaceae. Cottonseed of Malvaceae is also rich in oil and protein. Woody plants, such as camellia oleifera, walnut, olive, oil palm, tung tree and tallow, are sometimes classified as oil crops. The oil content of seeds of various crops is different, such as soybean, rape, sunflower, flax, camellia, safflower, etc. About 40%, sesame, peanut, castor, tung oil and butter are about 50%, and the oil content of coconut and oil palm seeds can be as high as 60%. After the seed oil is pressed, the cake residue still contains protein and other nutrients. Rapeseed-free cake contains glucosinolate sulfide, while castor cake contains toxic components such as ricinine and ricin, which can not be directly fed to livestock, and most of them can be used as high-quality feed.

Sugar crop: a crop that harvests the sugary part of plants and uses it for industrial sugar production. The location of sugar storage in plants varies with crops, such as sugarcane, reed millet and sugar maple in the stem, sugar beet in the root and sugar brown in the flower. Its main components are sucrose, glucose and fructose. The most common industrial sugar raw materials in the world are low-latitude sugarcane and high-latitude beet, and the sugar content is about 15 ~ 20%. Molasses and residues are by-products of sugar production and can be used as raw materials for alcohol or other chemical products. Rubus in Rosaceae and Stevia in Compositae contain glycosides, which are 300 times sweeter than sucrose, and can be used as sweeteners and auxiliary drugs for diabetic patients.

Beverage crops contains a certain amount of caffeine when it is harvested, which is a kind of crop that is exciting to human body when it is used as a drink. The young leaves of tea can be made into tea, and the seeds of coffee and cocoa can be processed into drinks. The caffeine content in the seeds of Caraganaceae plants is 2%, which is a strong stimulant and the raw material for making Coca-Cola soda. In addition, hops (commonly known as Cannabis) can be used as additives in brewing beer. It does not contain caffeine, but its inflorescence contains volatile oil, picroside, resin and tannin secreted by hops, which can make beer fragrant and slightly bitter, so it can also be classified into this category.

Seasoning crops will produce aromatic or spicy volatile substances. It is often used as an auxiliary material of food to promote people's appetite. There are mainly ginger in Schizophyllaceae, onion and garlic in Liliaceae, pepper in Solanaceae, mustard seed in Cruciferae and fennel in Umbelliferae. Woody plants such as Zanthoxylum bungeanum of Rutaceae, Pepper of Piperaceae, Cinnamomum cassia of Lauraceae, Illicium verum of Illicium, Illicium verum of Myrtaceae, etc. It also has this use.

Before synthetic dyes were widely used in dye crops, the sources of dyes mainly came from plants. Traditional dyes in China, the main raw materials of blue color are Polygonum blue leaves of Polygonaceae and Sophora japonica leaves of Leguminosae; Purple is mainly the purple root of Arnebiaceae; Red is mainly safflower corolla of Compositae and madder root of Rubiaceae. In Europe, the leaves of Isatis indigotica in Cruciferae are often dyed blue, the leaves of Indigo indigotica in Magnoliaceae are dyed deep yellow, the leaves of LYSIMACHIA christinae are dyed orange, and the tubers of Radix Curcumae in Coriander are dyed orange-red.

Rubber crop This crop contains white liquid latex, which is called rubber slurry. Its components are water, hydrocarbons, resin, grease, protein, sugar and raw rubber, which become elastic and tough rubber after solidification. The function of rubber pulp on plants itself is not clear, and it may have callus effect, but it is of great value to human beings and is an important industrial raw material. The widely planted woody rubber crops mainly include Euphorbiaceae rubber tree, Moraceae Panama rubber tree and Indian rubber tree. Herbs include rubber grass and rubber chrysanthemum in Compositae. There is also a gum tree in tropical America, and the gum produced can be used to make chewing gum.

Medicinal crops are cultivated plants containing alkaloids, glycosides and other organic compounds, which can be used to treat various human and animal diseases (see medicinal plants).

Feed and green manure crops are cultivated artificially to feed livestock and poultry (see pasture). After cultivation, green manure crops (see forage grass) are plowed or mowed in the vigorous growth period to increase soil fertility.

Aromatic crops contain hydrocarbon terpenoids and oxidized and sulfurized oils, which volatilize into the air and have an aromatic smell, and can be used to make cosmetics, food or smoked tea (see aromatic plants).

Crop nutrition and fertilization

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Generally, the water content of fresh plants is above 75%, and the remaining dry matter is mainly composed of carbon, hydrogen, oxygen, nitrogen and ash, accounting for 45%, 42%, 6.5%, 1.5% and 5.0% of the dry weight of plants on average.

Essential nutrient elements of plants

From 1640, after nearly three and a half centuries of exploration of elements, human beings finally figured out the essential nutrient elements for plant life in 1950s (1954).

The so-called plant essential nutrients are indispensable for plant growth and development. Without it, plants cannot complete their own growth cycle (from seed germination to growth, development to final seed setting). From 65438 to 0939, two American plant physiologists put forward three criteria for identifying essential nutrients. These three criteria are:

① Plants cannot complete their life cycle (or life cycle) without supplying this element.

② The role of this element in plant growth is irreplaceable by other elements.

(3) This element has a direct nutritional effect on plants, rather than indirectly improving the environment.

According to the above standards, scientists have determined that there are 16 kinds of essential nutrients for plants, namely: carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, boron, manganese, copper, zinc, molybdenum and chlorine.

Because the contents of these elements in plants are quite different, people divide this 16 element into two parts: macro elements and trace elements.

When the nutrient content of an element is between tens of percent and several thousandths, it is called a macro element, and when the content is below several thousandths, it is called a trace element.

Nine major elements: carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium and sulfur.

Seven trace elements: iron, boron, manganese, copper, zinc, molybdenum and chlorine.

According to the common situation of fertilization, it can be divided into:

Macroelement fertilizers: nitrogen, phosphorus and potassium fertilizer.

Medium element fertilizer: calcium, magnesium and sulfur fertilizer.

Trace element fertilizers: iron, boron, manganese, copper, zinc, molybdenum and chlorine fertilizers.

Although the content of carbon, hydrogen and oxygen in the working object is about 90%, it comes from carbon dioxide (CO2) in the air and water (H2O) in the soil, which is easy for crops to obtain. However, nitrogen, phosphorus and potassium need more, but they are supplied less in the soil, so they are often supplemented in the form of fertilizer.