Which of the following methods can minimize field losses in hay production?

Using preservatives at the time of harvest is an effective method to minimize field losses in hay production. When hay is harvested, it is susceptible to deterioration and spoilage due to environmental factors such as moisture and temperature. Preservatives help stabilize the forage during the drying process, thereby preventing the growth of molds and spoilage organisms. By maintaining the quality of the hay, these substances significantly reduce the risk of losses related to decay or reduced feed value.

Other methods highlighted, such as reducing cutting height, may lead to increased soil exposure and potentially higher levels of dirt in the final product rather than minimizing loss. Implementing crop rotation can enhance soil health and nutrient availability over time, but it doesn't directly impact the efficiency of hay production in terms of immediate field losses. Increasing moisture content tends to have the opposite effect by promoting spoilage and making the hay difficult to store and handle properly. Thus, the use of preservatives stands out as the most effective option for reducing losses during the critical period of harvesting and drying hay.