Anegative tropism is when a plant grows a stimulus.

The correct answer for the blank is-

A negative tropism is when a plant grows away from a stimulus.

Explanation:

Tropism is a biological process that indicates growth or turning movement of an organism, generally a plant, as a response to a particular environmental stimulus (any change in the environment that causes the organism to respond).

A negative tropism means the growth of organsim is taking place away from the stimuli.

Example- Growth of shoot of plant away from the gravity depicts negative geotropism.

increase soil erosion                                             reduce soil erosion

cattle grazing                                                         hydroseeding

deforestation                                                         contour plowing

                                                                                planting vegetation

plant roots basically hold the top soil

together and stop soil erosion because

in such situation top soil is not removed

during flood but cattle grazing causes

soil erosion because cattle consume the

grasses and herbs and top soil is exposed.

same situation occurs because of

deforestation, the trees and plants are cut

down to expose top soil which causes soil

erosion