Until about four decades ago, crop yields in agricultural systems depended mainly on internal resources, recycling of organic matter, built-in biological control mechanisms, and natural rainfall patterns. Agricultural yields were modest but stable and were achieved by growing many different types of crops in time and space and integrating animals in the same field which helped in suppressing insects, weeds and diseases and enhancing nutrient cycling. In these types of farming systems the link between agriculture and ecology was quite strong and signs of environmental degradation were seldom evident.

But as agricultural modernization progressed, the ecology-farming linkage was often broken as ecological principles were ignored or overridden. Modern agriculture confronts an environmental crisis and there is concern about the long-term sustainability of existing food production systems as they confront two waves of environmental problems: one is the huge use of artificial nutrients and their secondary effects and the second is the increasing of genetically modified crops.

It is clear that the waves of environmental problems in agriculture are deeply rooted in the prevalent socioeconomic system that promotes monocultures and the use of high-input technologies and agricultural practices that lead to natural resource degradation and biodiversity reduction. Such degradation is not only an ecological process, but also a social and political-economic process.

Reduction and especially elimination of agrochemical use require major changes in management that break the monoculture and provide diversity to assure adequate plant nutrients and to control crop pests. As was done not that many decades ago, polycultures, rotations, agroforestry and animal integartion can provide the ecological basis for a sustainable agriculture that does nor depend on agrochemicals nor transgenic crops.