A number of different factors can cause agricultural productivity to increase or decrease. It is important to note that productivity is not an absolute measure, but rather a reflection of the ratio between inputs and outputs. So a field that produces twice as much corn as it did in a previous year is not necessarily twice as productive; if the farmer spent twice as much on that field, the net change in productivity would be zero.
Some factors, like weather, are out of the control of the farmer. Unusual weather patterns, such as drought, a prolonged rainy season, early or late frosts, and other factors, can ruin crops and bring productivity down. The capacity of a given farm is also an important factor. Soil cannot be forced to produce beyond capacity, although there are methods that can be used to improve production capacity, such as fertilizing to add nutrients to the soil so that it can support more crops.
Pests can be another concern. In addition to spoiling crops, pests can also add significantly to the costs of producing a crop. Controlling them may require measures such as fencing, chemical treatments, or companion planting, all of which change the ratio of inputs to outputs.
Available equipment is another factor. In regions where access to mechanized farm equipment is low, agricultural productivity can also be low as people handle their crops primarily by hand. This involves a big investment of time, energy, and money, and also limits the total capacity of the land. Likewise, people with access to specialized seeds such as crop hybrids specifically developed to produce more can improve their productivity.
Innovation is a key factor for agricultural productivity. Farmers who can develop creative ways to farm smarter, as it were, will experience productivity increases. For this reason, many agricultural companies and nations invest in developing new farming techniques and in researching new approaches to farming. Studying ancient approaches to learn from prior generations can also play a role in agricultural innovation; sometimes the best method is already in use.
The supply and demand in the market may also play a role, because farmers will adjust their activities to meet the needs of consumers and this can have an impact on agricultural productivity. In some cases, governments even pay subsidies to farmers to compensate them for not growing crops, which can skew productivity measures.