THE INTERACTING NATURE OF LIMITING FACTORS ON CROP PRODUCTION

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Abstract
If crop yield is not maximum, it is due to the additive or synergistic accumulation of all stresses to which the crop is exposed. The stresses do not act independently. If yields are increased, it is because of removal or overcoming of stresses to approach the potential of yield maximum. If four different plant nutrients are present in supply and ratio each at 90% of optimum and if all other nutrients are optimum, the additive summation of the nutrient stress is 0.90 x 0.90 x 0.90 x 0.90 = 66%. Then 66% of yield maximum is possible if the interactions are sequentially additive. This assumes Mitscherlich-type limiting factors. Small departures of several nutrients simultaneously from optimum are thus a serious barrier to obtaining yield maximum. When Liebig-type limiting factors remain, little or no response to inputs to correct Mitscherlich-type limiting factors can be expected until those of the Liebig type are removed and in order of which is in greatest limitation. Once this type of limiting factor is removed, responses to additional inputs can be obtained. In contrast, it does not matter in which order Mitscherlich-type limiting factors are corrected. Severe deficiencies generally are of the Liebig-type, and slight deficiencies are of the Mitscherlich type. © Williams & Wilkins 1989. All Rights Reserved.