The most common environmental constraints are too little or too much moisture, temperature, or sunlight. Hail, lightning, and excessive wind can also injure plants. The soil environment can also have a profound effect on plant health. Soil texture, structure, pH, and organic and mineral composition are very important to plant growth and health. Air pollution can be from natural causes such as volcanic gases or artificial such as ozone and acid rain.
Air pollution can cause visible symptoms or reduce crop yield without other evidence of disease.
Other pollutants to air and water can result from accidental chemical spills. W.F. Bennett, Nutrient Deficiencies and Toxicities in Crop Plants, APS Press, St. Paul, Minn., 1993. M.C. Shurtleff and C.W. Averre, The Plant Disease Clinic and Field Diagnosis of Abiotic Diseases, APS Press, St. Paul, Minn., 1997. Diagnosis of Herbicide Damage to Crops, Chemical Publishing, New York, 1981. A Pictorial Guide to Symptom Diagnosis, Blue Crab Press, Virginia Beach, Va., 1988.