Effect of herbage mass per unit area and conditioning treatment on herbage drying rate

The rates of drying of herbage, cut from perennial ryegrass (Lolium perenne L.)--dominant swards and subjected to different treatments, were investigated under field conditions by changes in weight of herbage in wire mesh trays in 1995 and 1996. A series of replicated factorial experiments studied the effects, in different combinations, of intensity of conditioning achieved by passing the cut herbage through a laboratory-scale macerator zero (0C), once (1C), three (3C) or six (6C) times; weight of herbage per unit area equivalent to 450, 675 and 900 g dry matter (DM) m(-2). In one experiment, pressing the herbage to form a mat was incorporated into the experimental design. A further experiment investigated the effect of varying the proportion of conditioned herbage in the herbage mass from 0.00, 0.25, 0.50, 0.75 and 1.00 on drying rate. On each occasion the trays plus herbage were weighed at hourly intervals over an approximately equal to 6-h period and the DM content of the herbage estimated from the change in weight. On all occasions, conditioning and weight of herbage per unit area significantly (P < 0.001) influenced herbage drying rate. Lowering the weight per unit area of both unconditioned and conditioned herbage increased the rate of moisture loss. Unconditioned herbage at the equivalent of a herbage mass of 450 g DM m(-2) had a total moisture loss that was on average 1.5-1.8 times greater than unconditioned herbage at the equivalent of a herbage mass of 900 g DM m(-2). Similarly, conditioned herbage at the equivalent of a herbage mass of 450 g DM m-2 had a total moisture loss that was 1.8-2.3 times greater than unconditioned herbage at the equivalent of a herbage mass of 900 g DM m(-2). Increasing the level of conditioning produced a non-linear response in rate of moisture loss, consequently 3 passes through the macerator produced >0.95 of the total moisture loss that was produced by 6 passes through the macerator. Increasing the proportion of conditioned herbage in the herbage mass increased rate of moisture loss and consequently final DM content (P < 0.001) although there was little effect from increasing the proportion of conditioned herbage above 0.75. The effects of conditioning and weight of herbage per unit area treatments on total nitrogen, water-soluble carbohydrate and acid-detergent fibre concentration of the herbage were small.