May I suggest Howard T. Odum's works, in particular Environment, Power, and Society and Energy Basis for Man and Nature.

In the former he argues strongly about the mechanisms by which humans have enhanced ag productivity in plants and animals.

Generally, there are the following methods:

Mechanical tillage, breaking up soil to make it easier for plants to grow and spread roots. This also, incidentally, increases topsoil loss to wind and water, such that many farms are effectively "mining" topsoil faster than it's being replaced.

Artificial irrigation. This varies from simply collecting and distributing water via gravity-flow reservoirs and irrigation ditches to transporting water and irrigation pumps and pipes to water mines which, again, deplete a resource faster than it is restored -- as is the case throughout the eastern Plains states in the US, much of China, and especially in the Sahara and Arabian penninsula where water tens of thousands of years old is used to irrigate crops, from underground reserves which aren't being replenished. Water availability itself is becoming a significant concern, with major droughts in the past 5 years disrupting crops in Russia, the United States, China, India, and of course, as is rather chronically the case, Africa.

Fertilizer. Nitrogen, fixed at great energy cost from the air using fossil fuels (mostly natural gas). Phosphorus, which is in extremely limited supply. Potash, rather more abundant, but still with only a century or three of reserves at present rates of use.

Selective breeding. Plants and animals have only so much metabolic budget. By diverting energy away from specific uses, especially immune response, physical activity, and foraging needs, more can be devoted to growth. This works to an extent, but is greatly facilitated by ...

Antibiotics and pesticides to reduce illness and parasites. Fun fact: the first virus identified wasn't a human illness but the tobacco mosaic virus. Antibiotics and pesticides mean that animals and plants need devote less of their own energy to competing in their environment. Unfortuately, both ultimately create resistance, a problem later to both the ag products themselves and quite possibly humans, especially in the case of antibiotics. Moreover, bred cultivars requiring such treatments don't compete where they're not available (similarly for fertilized crops, above).

Mechanical pest reduction. Removal of weeds, or native long-lasting plants which compete for ag lang productivity (e.g., natural plains, tropical rainforest).

Solar panels compete directly with plants for solar energy. At best you want to put them in regions plants cannot grow.

The history of ag enhancement is relatively brief, but it's all been accompanied either by vast investments of energy, or by the application of either materials or technologies themselves requiring or based on vast applications of energy. Even the father of the Green Revolution, Norman Borlaug, cautioned that he'd only provided at best a brief respite from hunger.

It's not so long ago that major famines still ruled the world, with major instances in the 19th century (Ireland 1845-52 killing 1.5 million, China 1850-73 with a population drop of 60 million), and 20th (1920s in Russia, 5 million, and China, 3 million, 1930s Ukrain Holdomor, 7-10 million and China, 5 million, and the Great Chinese Famine of 1959-61, 15-43 million). And that's just a set of highlights, see: http://en.wikipedia.org/wiki/List_of_famines

In many cases, 30% of regional populations died (or in some lucky cases, emigrated elsewhere, as in Ireland), in others historically 50-90% of populations were wiped out. I'd suggest you not think this cannot happen again.

I'll also advise you that this is a topic I studied, extensively, in school.