Stressed experienced such crops could be due to abiotic factors (non living elements like climatic factors, soil and water related) or biotic factors (living elements like weeds insect, soil insects, fungi or bacteria)

Stresses due to soil
Soils properties are integral for sustainable productivity and quality of produce. Most of plants prefer a soil pH in the range of 5.5-.7.0 for their growth and development.Ideal soils for agriculture are balanced in contributions from mineral components 45% , soil organic matter (SOM, 5%), air (25%) and water (25%) The balanced contributions of these components allow for water retention and drainage, oxygen in the root zone, nutrients to facilitate crop growth; and they provide physical support for plants. The distribution of these soil components in a particular soil is influenced by the five factors of soil formation: parent material, time, climate, organisms, and topography. Each one of these factors plays a direct and overlapping role in influencing the suitability of a soil for agriculture.
Soil pH, which reflects the acidity level in soil, significantly influences the availability of plant nutrients, microbial activity, and even the stability of soil aggregates. Typically, soil pH values from 6 to 7.5 are optimal for plant growth; however, there are certain plants species that can tolerate - or even prefer - more acidic or basic conditions. Maintaining a narrow range in soil pH is beneficial to crop growth. SOM and clay minerals help to buffer soils to maintain a pH range optimal for plant growth.

Soil acidity
If the soil pH is below 7.0 , then it is classified as acidic soil. Soil below 5.5 often limits growth and development of crops. Under such conditions, plant often experience

  • Deficiency of nutrients such as Phosphorous, potassium, calcium, magnesium etc, due to their limited availability.
  • Nutrient toxicity (eg. Zinc, Iron, Aluminum, Manganese) due to increased availability due to solubilization
Soil alkalinity
Soils with pH more pH 7.0 are classified as alkaline soil. Soil above 8.0 limits growth of plants. Under these conditions plant experience
  • Nutrient deficiency (phosphorous, iron, zinc)
  • Soils are less fertile due to low soil organic carbon
Soils with high salt content
Soils are having high pH (above 7.5) and high soluble salts (Ca, Mg, Na). under these conditions plant experience
  • Poor growth due to osmotic stress (less uptake of water)
  • Over all deficiency of essential nutrients
Soils with heavy metal toxicity
Heavy metals accumulated in soils due to activities like mining, industrialization, excess use of agrochemicals etc. through plants these metals enter in our food chain and causes health hazards.

Soil cation exchange capacity (CEC)
The ideal content of the clay-humus complex (CEC) of is 60-70% calcium, 10-20% magnesium and 2-5% potassium, which always leaves 10% that can be filled with hydrogen.
CEC is an indication of the potential of the soil tohold plant nutrients by estimating the capacity of the soil to retain cations, on clay and organic matter which are negatively charged. Soils of CEC in the range of 15-30 meq/100 g is considered as ideal for cultivation of crops.

Temperature stress
Plants grows optimal in the temperature range of 25-35 C (77-95F), in tropical conditions) or 15-25C (59-77 F; temperate conditions). Temperatures above 35C (95F) often limits plant growth and plant experience
  • flower drop due to lack of pollination
  • poor fruit setting
  • leaf fall due to less availability of water
  • fruit cracking
  • overall decline in yield and quality
Temperature below 10C (41 F) plant experiences
  • low metabolic activities
  • Reduced growth rate
  • Leaf fall
  • Plants becoming dormant

Sub optimal temperature leads to freezing injuries leading to rupture of cell membrane and cell death

Water stress
Water is important for crop growth. Lack of water leads to plant death under severe conditions but under reduced availability of water plants experience
  • Low metabolic activities
  • Leaf fall
  • Fruit drop
  • Nutrient deficiency
  • Drying of leaves
  • Reduced flowering

Flooding of water has also deleterious impact on crops. The plants exhibits
  • Yellowing of leaves
  • Rotting of roots
  • High incidences of disease
  • Nutrient deficiency
  • Flower drop
  • Reduced fruit setting

Excess solar radiation
This often results in sun burning of fruits, leading to appearance of brown patches on fruit surface accompanied with deteriorates fruit quality and market value.

Biotic stresses
These are caused to various living elements

Fungal /bacterial pathogens
Causes number of diseases in leaves, fruits, and roots. Can attribute to significant crop loss

Insect pests

Sucking pests
Sucks plant sap which results in poor growth. They are often vectors for viruses causing damage to plants

Chewing insects
They eat the leaves and young shoots

Make holes in stem, root, fruits or shoots, resulting in drying of crop

Competes with main crop for nutrients and water. They usually grow faster than desired crop thus limits the growth and development of main crop.

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