Experiment 1: Specific Gravity of Corn Components

Table 1 presents the specific gravity of corn components as measured by the gas pycnometer. All components were oven-dried prior to measure­ments. Because of ambient rehydration, the MC of components varied between 2 and 8% at the time of measurements. The data presented in Table 1 were corrected on a DM basis using Eq. 1. Intact grain was signifi­cantly denser (1305 kg of DM/m3) than chopped stalk and leaf (average of 635 kg of DM/m3) or chopped husk and cob (average of 826 kg of DM/m3). However, when all material was ground through a 1-mm screen, there was no significant difference among the five components (average of 1546 kg of DM/m3). The corn used to measure specific gravity was very mature, being harvested in December, and had DM fractions of grain, stalk, husk, cob, and leaf of 65, 18, 4, 10, and 3%, respectively. Measures might be different for earlier maturity corn. However, the data show a remarkable homogeneity in specific gravity when material becomes very fine.

Experiment 2: Sequential Water Separation

Table 2 presents the physical characteristics of the four silages used for the sequential water separation experiment. The two processed silages (Ziegler Farm and Arlington Farm) had very similar MPL (13 and 14 mm, respectively). They also had a relatively low MC; the Arlington silage had the highest DM content (36% DM). The Prairie-du-Sac Farm silage was unproc­essed and had a long particle size (17 mm), whereas the Binversie Farm silage was unprocessed and had a short particle size (8 mm). The moisture reported for grain and stover in Table 2 may slightly underestimate the actual values because components were exposed to natural air-drying for about 1 h during manual sorting prior to oven-drying.

Table 3 shows the proportion of grain and stover in the sunk material from the four silages. After the first separation, the grain concentration in the sunk material was 75% and highest for the Arlington silage, which also was the driest. The grain concentration was only 41% and lowest for the Prairie — du-Sac silage, which was the wettest. The Binversie silage was different from the other three silages because it produced a higher amount of sunk grain (31% of total DM) than the three other silages (19% of total DM). This might be the result of a later maturity harvest; a greater presence of fully formed kernels; and no used of a processor, thereby leaving more intact grain.

After the eighth separation, grain concentrations ranged from 27 to 46% and were lower than after the first separation. At each separation, more stover sank and mixed with the corn grain. Only the Arlington silage released more than 1.5% of total DM as grain beyond the first separation. The actual concentration of DM in the effluent ranged from 0.71 to 1.22%, with an average of 1.01%. DM in the effluent reported in Table 3 represents the DM as a proportion of the original DM in the silage.

Figures 1 and 2 illustrate the curves of sunk grain, sunk stover, DM in the effluent, and floating material over the course of the eight water sepa­rations for two contrasting cases: the Arlington Farm silage with a low MC and the Prairie-du-Sac Farm silage with a high MC. The sunk grain and sunk stover reported in Figs. 1 and 2 were measured at each separation.

Table 3 Grain and Stover Proportions After the First and Eighth Separations of Fresh Silage in Water in Experiment 3 Silage source After first separation After eighth separation DM (%) Grain concentration in sunk material (%) DM (%) G ain concentration in sunk material (%) Sunk grain Sunk stover Sunk grain Sunk stover Floating stover DM in effluent Ziegler Farm 18.5 b 11.4 bc 62.0 b 20.0 c 36.3 b 17.6 b 26.0 a 35.6 b Prairie-du-Sac Farm 19.1 b 27.1 a 41.3 c 19.5 c 53.2 a 6.7 c 20.7 b 26.8 c Arlington Farm 19.3 b 6.6 c 75.2 a 25.2 b 29.6 c 23.8 a 21.6 b 45.9 a Binversie Farm 30.7 a 14.7 b 67.7 ab 31.6 a 37.2 b 10.2 c 21.0 b 45.9 a SEM 1.7 2.3 4.9 2.1 2.1 1.7 0.4 3.5 LSD 3.9 5.3 11.2 4.9 4.9 3.9 1.2 7.5 a Average of three replications. Values with the same superscript letter in a given column indicate no significant difference (p < 0.05). SEM, standard error of means; LSD, least significant difference.

The floating material and the effluent DM were measured only after the eighth separation. The curve for DM in the effluent was inferred by assum­ing that 70% of DM in the effluent was released after the first separation (see experiment 3 for a justification) and by assuming that the release followed a logarithmic curve. The curve for floating material was obtained by mass balance. The suspended stover recovered after the first separation was considered to be part of the floating material.