Definition of stresses in crop production—iron, plant nutrient, and non‐nutrient stress interactions

Abstract

A stress in crop production is considered as something that decreases yield, and a growth promoter is something the increases yield. Officially, granting and governmental agencies consider that many inputs that improve crop production as not being related to stress. In other words, a stress is an external factor that decreases crop yields from yield maximum to a lower level. Examples are diseases, insects, salinity, and excesses of trace elements. Granting agencies have not considered plant nutrients, growth regulators, or genetic limitation as being directly related to stresses; rather, these factors are considered as promoters of plant yields. This is a fallacy. When plant nutrients are not in optimum amounts and ratios, their deficiency and imbalance are true stresses; they decrease crop yields just as do other stresses. If a yield is not maximum, it is due to the additive accumulation of all stresses. If yields are increased, it is because of removal or overcoming of stresses. Nutrient deficiencies and imbalances are yet a major barrier or stress to obtain the potential of yield maximum. If four different plant nutrients are present in supply and ratio at 90 per cent of optimum and all other nutrients are optimum, the summation of the nutrient stress is 0.90 x 0.90 x 0.90 x 0.90 = 0.66 or 66 per cent of yield maximum. These small departures from optimum collectively are a serious barrier to obtaining yield maximum. In a pot test, iron limited growth of soybeans about 10 per cent, even though there was no chlorosis. This illustrates the importance of research on iron and other plant nutrients and deserves consideration for funding as stress research.

Key words:

• Limiting factors
• additive effects
• synergism
• iron
• phosphorus
• nitrogen

Notes

The Laboratory of Biomédical and Environmental Sciences is operated for the U.S. Department of Energy by the University of California under Contract No. DE‐ACO3–76‐SF00012.