Competition occurs when two species compete over a restricted resource that is necessary for their survival. Water, nutrients, light, and space are the primary components for which competition is usually present. When crop plants and weeds have similar vegetative habits and demand for available growth nutrients, competition is most intense. In general, an increase in weed growth equals a decrease in crop growth of one kilogram.
Principles of crop weed competition
Competition for nutrients:
Weeds absorb mineral nutrients more quickly than many agricultural plants and store them in greater quantities in their tissues. Weed removal of nutrients causes a massive loss of nutrients in each crop season, with weeds losing twice as much potassium as crop plants.
Competition for moisture
Weeds, on average, transpire more water than most agricultural plants to produce the same quantity of dry matter. It becomes increasingly important as soil moisture stress increases, as it does in arid and semi-arid environments. C4 plants, on average, use water more efficiently, yielding more biomass per unit of water. The transpiration rate of Cynodon dactylon was nearly twice that of pearl millet.
In weedy fields, soil moisture may be depleted by the time the crop reaches the fruiting stage, which is the crop’s peak consumptive consumption period, resulting in considerable crop yield losses.
Competition for light
It can start very early in the crop season if the crop seedlings are suffocated by extensive weed growth. When moisture and nutrients are plentiful, it becomes a key component of crop weed competition. In dry land agriculture, crop weed competition is limited to nitrogen and light in years with regular rainfall. Increased light intensity, unlike competition for nutrients and moisture, cannot help a crop plant after weeds shade it.
Competition for space (CO2)
Crop weed competition for space is a requirement for CO2, and it can arise when plant communities are excessively crowded. C4 type weeds may use CO2 more efficiently than C3 type crops, which may contribute to their faster development.
Critical period of weed competition
The shortest time window during crop growth when weeding yields the best economic returns is known as the critical period of weed competition. The key period for agricultural weed competition is the time from sowing to maintaining the crop in a weed-free environment in order to get the best economic output. In general, in a 100-day crop, the first 35 days following sowing should be kept weed-free. It becomes evident that different crops require weed-free conditions for 2-8 weeks in general, which underlines the importance of timely weed treatment, without which crop yields are dramatically reduced.
Factors affecting the competitive ability of crops against weeds
– Density of weeds: It is a common occurrence for weed density to increase as yield decreases. However, it is not a linear relationship because a few weeds have a smaller impact on yields than others, and hence it is a sigmoidal relationship.
– Crop density: Plant population increases minimize weed growth and competition until they become self-competitive. Agricultural density and rectangularity have a big role in determining how much and what kind of crop environment weeds can grow in. Weed growth can be induced by wide row spacing combined with a large intrarow crop plant population. In this respect, square planting of crops in which there are equal row and plant spacing should be ideal in reducing intra crop plant competition.
– Type of weeds species: The sort of weeds that grow in a certain crop has an impact on the competition. The presence of a specific weed species has a significant impact on the crop-weed competition. E. Crusgalli in rice, Setaria viridis in corn, and Xanthium sp. in soybean, for example, have an impact on crop yield.
– Type of crop species and their varieties: Crops and cultivars differ in their ability to compete with weeds; for example, barley, rye, wheat, and oat are listed in decreasing order of weed competing ability.
Barley’s high resistance to weed competition is attributed to its ability to generate more widespread roots during the first three weeks of growth than the others. Weed competition is less of an issue for fast canopy developing and tall crops than it is for slow growing and short statured crops. Due to their sluggish growth and early development, dwarf and semi dwarf crop varieties are more sensitive to weed competition than tall varieties.
– Climate: Because most of our crop plants are subject to climatic pressures, adverse weather conditions, such as drought, excessive rain, and temperature extremes, will favor weeds. It becomes more worse when agricultural cultivation is stratified across marginal lands. All of these factors reduce a crop’s natural ability to combat weeds.
– Time of germination: In general, Crop Weed Interference occurs when the period of crop germination coincides with the emergence of the first flush of weeds. Sugarcane takes around a month to germinate, whereas weeds germinate in a fraction of that time.
– Cropping practices: Cropping strategies such as planting method, crop density and geometry, as well as crop species and kinds, all have a significant impact on Crop Weed interference.
– Crop maturity: Another aspect that influences weed-crop competition is the crop’s maturity. Due of the crop’s good establishment, weed competition lessens as the crop gets older. Weeding during the early stages of the crop’s growth increases output greatly.