Developing the field of physiological ecology allowed ecologists to determine to these patterns mechanisms. Raunkiaer classified plants according to the location of the perenniating organs. The implications from studies like this is that morphological differences among species have physiological implications. A third impetus comes from the physiology of agricultural crops . Therefore, physiologists and agronomists who studied physiological responses to stress became curious with native plants that could cope with these environments without deleterious effects.
Agriculture is a major polluter of ground water and aquatic systems.
Scientists looked for ways to reduce fertilizer inputs and to improve retention by crops. As human populations expand, agriculture must move into marginal habitats. In areas like the Amazon Basin and the African Sahel, often economics preclude expensive fertilizer and irrigation. Scientists looked for ways to develop crops that use water and nutrients more efficiently. Agronomy has moved toward trial and error selection programs, focusing less on physiological mechanisms.