hydrophonics
The temperatures went up and the growing season was increased
An incredible amount of different things. It would be impossible to list them all. Not only chemicals but also ways and methods of growing.
Any kind of cross pollination will improve crops or plants due to a greater variety of genetic information.
Genetic engineers have devised ways to improve crop yields through eugenics, which refers to hereditary improvements. They have also developed methods to make crops more resistant to pests.
Approximately 11% of the Earth's surface is suitable for growing crops. This usable land is primarily found in regions with favorable climates, soil conditions, and access to water for irrigation.
Because different crops behave differently in the same or different growing/climatic conditions. Losses for oilseed crops are different than cereal crops, for instance.
To increase their resistance to disease and predation. To improve the yield. To allow crops to grow more quickly and in more adverse conditions. To reduce starvation in the world.
Irrigation, if there's any water at all. Some methods of irrigation, such as drip tubes, use very little water and can keep the crop growing quite nicely. If there is no water available, then perhaps growing low-water-use species might work.
One condition that is best for growing crops is a lot of rain. Another condition good for growing crops is a warm climate and good soil.
It's good for rice to be in flooded areas at a temp of 70 F (21 C).
Different crops require different growing conditions. In some areas, cereal crops (wheat, barley) grow well. Other areas may be better suited to the growing of oats, beans and root crops. The weather and the season, where the crop is to be grown (in the north of Scotland, or in the south of England, can make a huge difference), the soil constituency (loam, sandy, clay) also make growing some crops unsuitable in some areas.
Prairie soil will be best for growing crops.