# Experimental Study on Drying Characteristics of Alfalfa Hay Bales Using Hot Air Convection
## 1 Introduction  
Alfalfa, as a nutritious and highly adaptable forage crop, plays a significant role in enhancing the efficiency of livestock production and promoting ecological protection [1]. With the rapid increase in demand for livestock and dairy products, the cultivation of alfalfa in China has been growing annually, and the quality of alfalfa hay has attracted widespread attention [2]. Currently, the primary method for harvesting and processing alfalfa hay is field drying. After moving, alfalfa is left to dry in the field until its moisture content reaches the safe level of 14-17% (w.b.). It is then baled and stored mechanically. However, during the mechanical baling and collection process following field drying, a significant amount of the nutritious leaves and flowers of the alfalfa hay are lost, falling into the field. The proportion of loss ranges from one-quarter to one-third. In rainy weather, prolonged moisture exposure exacerbates nutrient degradation and microbial spoilage, leading to even greater losses in both yield and nutritional quality [3]. When the moisture content of freshly mowed alfalfa is around 40% (w.b. ), the toughness of the connection between the leaves and stems is at its strongest. Baling operations at this stage can effectively preserve the most nutritious parts of the alfalfa--its flowers and leaves--within the bales. After baling, the density of alfalfa hay bales ranges from 110 to 180 kg/m\({}^{3}\). Alfalfa haybales with a moisture content of 40% (w.b.) are still subject to respiration and oxidation. Artificial drying methods are required to quickly reduce the moisture content to below 20% (w.b.). Otherwise, the interior of the bales will turn yellow and rot, leading to a decline in the quality of the alfalfa hay [4]. Therefore, researching efficient and controllable drying methods is of great significance for reducing the loss of nutrients in alfalfa, improving the quality of dried hay, providing high-quality feed for the livestock industry, and promoting the large-scale and modern development of the alfalfa industry. Research on alfalfa drying technology mainly focuses on the optimization of the initial state, improvement of drying methods, and precise control of drying parameters. In the current production process of alfalfa hay, the initial state of alfalfa is the first issue to be considered, for example, the initial moisture content, which is generally affected by harvesting methods [5; 6] and harvesting time [7]. According to research by [PERSON] [8], a higher initial moisture content during ensiling can lead to increased contents of neutral detergent fiber (NDF) and acid detergent fiber (ADF) in alfalfa, thereby affecting its nutritional value. Additionally, the uniformity of the hay bales is also a key factor affecting drying efficiency. [PERSON] et al. [9] found that a uniform bale structure helps hot air penetrate better, thus improving the drying effect through their research on round bale drying equipment. [PERSON] [10] pointed out that the moisture content of thick-layer alfalfa can be reduced from 80% to 10% in just 40 min at an air temperature of 200 \({}^{\circ}\)C, but as the thickness of the alfalfa increases, the drying efficiency decreases significantly. [PERSON] [11] studied the impact of alfalfa hay bales on solar drying characteristics and found that the lower the bale density, the better the drying effect. In terms of drying methods, common drying technologies currently include natural drying [12], hot air drying [13], infrared hot air drying [14], microwave drying [15], and solar drying [16]. Natural drying, although low-cost, generally has a drying rate that is positively correlated with solar radiation and is highly restricted by weather conditions, resulting in long drying times and severe nutrient loss [17]. In comparison, hot air drying and infrared hot air drying have attracted more attention due to their high efficiency and controllability.