Besides introducing robusta coffee to the world market, the battle against rust had another important consequence for coffee agriculture -- the widespread conversion of plantations from shade to full sun. Cultivators believed that drier conditions would prevent the fungal rust from spreading. At the same time, they discovered that growing coffee in sunshine could increase short-term productivity, as long as they increased their applications of pesticides and fertilizers to help sustain the increased yields.
In most Latin American countries outside of Brazil, coffee has traditionally been grown under a shady forest canopy. The trees provide a microclimate favorable to coffee -- reducing the range of temperatures on the plantation and offering shelter from wind, storms, and overexposure to sun. (While full sun increases yields in the short term, it depletes the soil over time.) Additionally, nitrogen-fixing trees of the forest keep the soil rich in nitrogen, a critical nutrient. Leaves and other detritus create a natural mulch that keeps the soil fertile and reduces erosion. Although growing coffee in the shade is labor-intensive, requiring weeding and harvesting by hand, it reduces the need for large-scale applications of synthetic fertilizers and pesticides.
"Sun-coffee" plantations need continual inputs of pesticides and fungicides to control biological enemies that thrive in coffee monocultures, as well as nitrogen fertilizers to replenish exhausted soil. Removing the forest's network of roots and natural mulching, increased erosion becomes a problem as well.