Until about four decades ago, crop yields in agriculture depended mainly on internal resources, recycling of organic matter, built-in biological control mechanisms and rainfall intensity and frequency. At that time, agricultural yields were modest, but stable. Production was safeguarded by growing more than one crop. Inputs of nitrogen were gained by rotating major field crops with legumes. In turn rotations suppressed insects, weeds and diseases by effectively breaking the life cycles of these pests. Most of the labor was done by the family with occasional hired help.
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