Abstract:

This study comprehensively analyzed the dynamics of drying rate and nutrient content during natural drying of alfalfa （Medicago sativa） in irrigated regions to better understand the key environmental factors influencing alfalfa hay drying. Meteorological and soil moisture data were collected and plant traits including water content， and major nutrient components （crude protein， CP； crude ash， Ash； ether extract， EE； neutral detergent fiber， NDF； acid detergent fiber， ADF； water-soluble carbohydrate， WSC； and relative feeding value， RFV） were measured in alfalfa with flattened stems harvested using mechanical equipment， at different cutting dates. The processes of water loss and nutrient changes were analyzed， and key environmental factors affecting drying rate and nutrient dynamics were identified through correlation analysis. Furthermore， the study divided the natural drying process of alfalfa into physiological （from cutting of alfalfa to when the whole-plant moisture content decreased to approximately 40%） and biochemical （the whole-plant moisture content decreased from 40% to 18%） drying stages， and analyzed and compared these two stages respectively. The results showed that： 1） The physiological drying stage accounted for 19.80%-52.25% of the total natural drying process， with the proportion decreasing gradually as cutting dates from May to September were delayed. During the physiological drying stage， drying rates followed the order： leaves>whole plant>stems； in contrast， the biochemical drying stage exhibited the order： stems>whole plant>leaves. Drying rates of stems， leaves， and whole plants in the physiological drying stage were 1.79-， 7.69-， and 3.43-fold higher， respectively， than those in the biochemical drying stage. 2） Contents of CP， WSC， EE， and RFV decreased throughout the drying process （including the beginning and end of drying， for both physiological and biochemical drying stages）， whereas Ash， NDF， and ADF contents increased. Losses of EE， RFV， WSC or gains of Ash， NDF， ADF occurred during the physiological stage， with loss rates ranging from 52.09%-75.00% and gain rates from 48.53%-62.94%. CP loss primarily occurred during the biochemical drying stage， accounting for 71.18%-75.82% of total loss. 3） During alfalfa drying， environmental factors influenced drying rate in the order： air temperature>solar radiation intensity>wind speed>air relative humidity>0-10 cm soil moisture. The key factors （air temperature， solar radiation intensity， and wind speed） showed significant （P<0.05） or highly significant （P<0.01） positive correlations with drying rate. Nutrient content in alfalfa hay was primarily affected by air temperature， wind speed， air relative humidity， and 0-10 cm soil moisture.

Key words: alfalfa, natural drying, environmental factors, drying rate, nutritional quality