What is a Crop vs. Weeds in Agriculture:
A Perspective

What is a crop? What are crops? What are weeds? These are elementary questions and for those who have undertaken formal study of the basics of agriculture, they may seem to be unnecessasary questions. Are they?

Nonetheless, for the beginners at least, it is important to be clarified on the terms. The clarification becomes more relevant in view of the increasing concerns on the environment and biodiversity conservation. It is in connection with these concerns that cutting of trees has become an issue of absolute right or wrong.

Various dictionaries will show that the word “crop” has multiple meaning. Some of these are completely different from the other so that one who is familiar with the use of the word in one instance may be confused when the same word is used differently. For example, the word can refer to a harvested produce such as grains, fruits, etc. It is also common in computerized trimming of photographic images.

In agriculture, the terms crops and weeds have already been attached to many plant species without qualification. Corn (maize), sugarcane, coconut, etc. are automatically listed as agricultural crops because they are always grown intentionally for some purpose. Their economic importance are already established. Conversely, many plants are listed as weeds (e.g. cogon or Imperata cylindrica, aguingay or Rottboellia exaltata, purple nutsedge or Cyperus rotundus, etc.) because they always grow unintentionally and hamper with or cause adverse effects on the growth of crops. But there are much more about these terms.

What is a Crop: Useful vs Unuseful Plants

This paper refers to the crop (pl. crops) which is short for agricultural crop. It is a term which is commonly defined in the simplest way as a plant which is useful to man. It can be an agronomic crop, a horticultural crop or agroforest crop, or classified further under more specific grouping such as food crops, non-food crops, cereals, grain legumes or pulses, etc.

In contrast, a weed is a plant which is unuseful or a plant which grows where it is not wanted. The main distinction, therefore, between crops and weeds in agriculture is that crops are useful while the contrary applies to weeds.

Nicely and easily stated. But not quite clear. To better understand what is a crop and what is a weed, it is essential that the words “useful” and “unuseful” be clarified. It is therefore necessary to delve first on the question “Are there plants which are not useful to man?” The answer should be No. All plants are useful to man. If not directly, then indirectly.

With rare exception, plants photosynthesize in which process the energy from the sun is converted to chemical energy and trapped in organic compounds. This chemical energy from plant-based food is utilized by man and other heterotrophic organisms to fuel their life processes.

Photosynthesis in plants also generates oxygen which is essentially needed in aerobic respiration. In addition, the carbon component of the absorbed CO2 is used as structural bases in building organic, or carbon-containing, compounds including complex carbohydrates, proteins, fats and oil. Upon decomposition, all plants also enrich the soil or contribute to soil-making.

So why is it that the description “useful” is equated with what is a crop? If all plants are useful, then all plants should be crops and none will qualify as weeds. Consequently, there would be no need to invent the term weed in agriculture. But both terms exist and are continually used.

Again, what is a crop?

Crop and Weed Further Distinguished

It is likewise important to be able to distinguish what is a crop from weed. To reemphasize, the term crop refers to agricultural cropa plant which is useful to man and thus grown intentionally or otherwise taken care of. It means that said plant has a use or uses to a person or group of persons as a source of food or feed, cash, or some other obvious benefits, including its usage in ornamental horticulture and for special purposes such as shade crop, cover crop, green manure, windbreak, erosion control, etc. Thousands of uses can be enumerated.

But there are no hard rules on which particular uses apply to a specific plant. It depends on the needs of particular persons, subject to certain time-specific plans and purposes. Another consideration is the inherent characteristics of plants. Some plants yield abundant fruits, while others produce seedsmodified roots and stemsleavesflowersfiber, oil, etc. with commercial demand. For a subsistence farmer, the potential of a plant to supply food and basic needs to the family is the main consideration in growing it or in preserving and managing a naturally growing plant.

Further enlightenment on what is a crop should likewise be extended to the concept of weeds. Weeds have been defined as plants which are unuseful. The concept of weeds could possibly have started with the ancient man when he begun to domesticate plants. He had to remove the nearby plants, including vines, which interferes with the growth of and access to selected plants which grow in the wild.

However, the application of the word “unuseful” or “useless” or "not useful" to weeds is somewhat confusing because, as earlier noted, no plants are absolutely useless. Also, it doesn’t much help in clarifying what is a crop because these words (unuseful, useless and not useful) are mere antonyms of “useful”. A modified definition is more enlightening and descriptive of the change in the concept of a weed: A weed is a plant which grows where it is unwantedStated another way, it grows on a particular spot in which it is not wanted or not needed.

This definition of weed eliminated the misleading connotation from the use of the word unuseful or useless that some plants are indeed without any use. It means that any live plant can be a weed depending on where it grows. It does not matter whether it is an annual, biennial or perennial, or it belongs to any botanical or crop classification, or a seedling or adult, or a native species or introduced.

The basis of a weed is its location in respect to some other plants (the crop) which grow or are intended to be grown for some use or useful products. If it is there where it is unwanted or not needed, or it hampers with the growth of a crop, then it is a weed. The same effect occurs when a plant prevents movement or passage or any farming operation within the farm. Likewise, some introduced plant species have become causes for concern because of their damaging effect on biodiversity. These include the neem tree (Azadirachta indica) which has been identified as an invasive alien species (IAS).

Interchangeability of the Terms

For more clarity on what is a crop, it should be apparent also that any crop, although already established as an economically important plant, may not always remain a crop. Any crop can become a weed. Corn is one of the major crops in the world, but when it grows unintentionally in a plot which is intended solely for a certain vegetable then it (the corn) becomes a weed. Trees provide shade and other benefits, but when they cause inhibitory effects on fruit crops in the orchard or on forage crops in the pasture then they become weeds.

Some plants or trees can even become weeds within the same species. When plants are closely spaced, thinning or the removal of excess plants is usually the final resort.

Conversely, a weed may become a crop. Some examples: In some localities, the cogon grass (Imperata cylindrica) has been managed and harvested for roofing; grass weeds have been utilized as source of forage for grazing animals and an ingredient in vermicomposting; and some weeds have been retained intentionally and used as herbal medicine (e.g. ringworm bush, sunting or Cassia alata) or as source of vegetable (e.g. jute, saluyot or Corchorus olitorius and amaranth, kulitis or Amaranthus spinosus).

The concept of a weed is similar to that of nuisance. When something becomes a nuisance, a person affected will likely cause its abatement (or removal). Similarly in crop production, clearing, weeding, and thinning are standard operations.

Disclaimer: This elaboration on what is a crop should not be interpreted as promoting the indescriminate cutting of trees. The author himself has actively participated in the production of planting materials and in the growing of fruit trees and bamboo. Rather, exacting decisions are anchored upon correct information.

(Ben G. Bareja July 2012)

Read more: Invasive Plant Species

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