In modern agroecosystems in favorable agricultural areas there are two main challenges. First, the current practice of high external input agriculture is not sustainable. The resulting high outputs (i.e., high yield) often come at the expense of the natural resources base (water, soils, biodiversity), both on-farm and off-farm. Yield plateaus of major crop species in high production areas have been reported, causing concern regarding the sustainability of on-farm production. The heavy dependence on agrochemicals (including pesticides and chemical fertilizers) in uniform production systems can result in the destruction of a wide array of susceptible species in the ecosystem7 and pollution of water sources. Intensive cultivation with irrigation can lead to rapid water depletion and salinization of the soil. Future as well as present generations are affected, since valuable stores of genetic resources in natural habitats may be irretrievably lost.8
Second, genetically homogenized production fields are vulnerable to significant risks and losses over time, especially from increased vulnerability to pests and diseases. A plant pest or disease can be devastating if it infests a uniform crop, especially in large, homogeneous plantations. Producers have suffered serious economic losses from relying on monocultural varieties,2 as when a root disease destroyed vineyards in France and California in recent decades and a virulent disease devastated banana plantations in Central America in this century.
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