Seen from the outside, agriculture may seem to be a magical process: things are planted in the soil, cared for during a season, and food is harvested eventually: from useless dirt, the world is fed. But when farmers go into their fields and harvest the year's crop of wheat, peppers, or watermelon, they know that they're not creating food out of anything. They know what came into their field (the work they put in, the bio-manure they brought as fertilizer, the insecticides they introduced for pest control), and understand that agriculture is not an operation of creation but of transformation. Food does not spring out of the ground: raw resources are transformed into food through a lot of work, and a lot of brainpower. And the root of this transformation happens within the plants themselves, who take nutrients from the soil and energy from the sun and support seven billion people and the whole of life on earth.
But plants were not made by human beings: they appeared through natural processes millions of years before the first mammal even stepped a foot on our planet. As such, they are regulated by processes that were not made by us; we human beings merely channel and instrumentalize those processes to feed ourselves. Same as the natural processes underlying soil fertility, water availability, nutrient retention, soil structure maintenance, pest control, and even seed saving: all of them were active way beyond human beings began harnessing their power for their benefit.
The basis of agriculture is, thus, ecology; the principles and processes that guide how ecosystems work. There is no agricultural activity that is not based on ecological processes: there is just agriculture that is consciously based on them and that, as such, becomes sustainable, and agriculture that unwillingly goes against ecological processes and, as such, is unsustainable and leads to hunger crises and environmental troubles of all sorts. Organic agriculture is agriculture practiced through the most scientifically-informed techniques for managing agricultural land as an ecosystem. It is a system of practices that collaborates with, rather than fighting against, the very natural processes that gave origin to live on earth — as such ecology is another of its principles, alongside health, fairness, and care. In fact, it might be said to form the basis of them all.
A quick glance at the myriad natural processes underlying soil degradation, which organic agriculture takes into account to prevent the loss of fertile soil, gives a good impression of the connectedness of agriculture to ecology as one of its foundational principles.