How does this relate to agriculture?
The daily change of temperature and the seasonal changes of weather are both effects of the delicate balance of incoming sunlight and outgoing longwave radiation. On a clear and windless day, the temperature will rise following the course of the sun. But even after noon, when solar radiation begins to decline, temperatures will continue to rise because the land is trying to reach a balance of incoming and outgoing energy. In winter when days are short, the peak temperatures can occur 2-3 hours after noon. In summer when days are longer, it can be 4 to 5 pm before the highest temperatures are reached. The coolest temperatures usually occur just around sunrise when no sunlight has hit the ground for several hours. Planning fieldwork late in the afternoon is more likely to result in ill effects of high temperatures and heat exhaustion in summer because of this thermal lag.
The seasons also reflect the attempts of the earth to balance incoming and outgoing energy on a larger scale. Just like the lag of temperatures on a day, the hottest summer temperatures occur after the maximum sunlight has been reached. In the Southeast this generally happens about a month after the summer solstice (when the sun is highest in the sky at noon). Similarly, the coldest temperatures tend to occur about a month after the winter solstice in December.