Abstract: n this study, the determination of density, porosity and permeability rates of sunflower silage at different stages of maturity and under different conditions of compaction was aimed. Whole-plant sunflower (Helianthus annuus L.) was harvested at three different maturity stages; (BA, Beginning of Anthesis (78%), ML, one-third Milk Line (70%) and BL, Black Line (64%)). Five compaction levels were done during ensiling. These were control (no compaction), vacuum and compaction with 150 kPa (C₁), 248 kPa (C₂) and 498 kPa (C₃). The chopped forages were ensiled in PVC (5.7 L) mini-silos. For porosity measurements, a tube system was designed, which operated according to ideal gas law. Permeability was measured to be the time during, which 1 L water passed through the silo container. The results of this study showed that the values of porosity, permeability and density were found to be significantly affected by the applications of compaction and stages of maturity.

INTRODUCTION

Porosity value is one of the significant factors that are used for well-quality ensilage. How well a crop is preserved by ensiling depends on minimizing exposure to oxygen during storage and feed out (Muck and Holmes, 2003). While, the quality of the seal is the key factor in influencing oxygen exposure during storage, the porosity of the silage is the principal factor affecting oxygen movement into the feed-out phase of the silo once the silo is opened for emptying. If a silo is not covered or the seal is substantially damaged, the rate of spoilage losses during storage will be affected primarily by silage porosity as well. Porosity is a function of the density and moisture content of the crop (Pitt, 1986). Consequently, in horizontal bunker or drive-over pile silos the packing practices during filling are important in determining the density and porosity of the silage and the silage's subsequent susceptibility to spoilage losses during storage and feed out (Muck et al., 2004).

Pressure had a significant impact on increasing the density of corn. Density is an important factor in the final quality of silage (Roy et al., 2001). High density will result in a low porosity and therefore, reduce air infiltration in an imperfectly sealed silo (Rees et al., 1983). A high silage density is desirable to increase storage capacity and to reduce porosity, thereby reducing oxidation loss and preserving a high feed value. However, obtaining a high silage density can be expensive because of requirements for heavy compaction equipment, prolonged compaction time, suitable layer placement and thickness (Savoie et al., 2003).

The permeability of silage is of great significance in aerobic deterioration. It is theoretically related to porosity (Williams, 1994). Permeability of alfalfa hay decreased with increasing moisture levels and pile depth (Ahn et al., 2007).

Whole crop sunflower can be used to ensile, but the ensiling and nutritional quality depends upon the stage of maturity at the time of harvest (Tan and Tumer, 1996; Garcia, 2002; Toruk, 2003).

The objective of this study was to estimate the effects of the density, porosity and permeability rates of sunflower silage under three maturity stages and five compaction levels.

MATERIALS AND METHODS

Sunflower (Helianthus annuus L.) used in this experiment was sowed in April, 2006 during the summer growing season.

Fig. 1:	Trial set for compaction and load measure

The variety of sunflower used in this experiment was Meric F1. The experiment field consists of two plots used for wheat and sunflower rotation for several years. Seeding rate was 140,000 seeds ha^-1 with 70 cm row width and 8 cm with planting depth. Sunflower was harvested at three different maturity stages. These were the Beginning of Anthesis (BA), one-third Milk Line (ML) and Black Line (BL).

A conventional silage machine with a single row was used for harvesting. The average particle length of chopped sunflower was 11 cm. The chopped forages were ensiled in PVC (5.7 L) mini-silos (Peterson, 1988).

The chopped material was filled with compaction and vacuum mechanisms. Trial set for compaction is shown in Fig. 1.

The set has mainly four units. These are battery, numeric indicator, for converting signals (come from load cell) to numeric value, computer, for recording numeric values (coming from the numeric indicator) and load cell, for converting force to signal. ESIT, TCS 500 model load cell was employed by means of the shear box method. A laptop computer and ProComm software were used to evaluate the numerical values.

Sunflower was ensiled with the following vacuum and compaction methods.

To apply vacuum; mini-silo lids were fitted with a water-filled gas-release valve and the valves were closed by vacuum from vacuum pump (McEniry et al., 2007).

Fig. 2:	Porosity measurement apparatus (Kocabiyik et al., 2004)

After 50 days, all mini-silos were opened for determining density, porosity and permeability rates.

Determination of density: Density was determined by the following Eq. 1:

(1)

where:

Determination of porosity rate: Porosity, pore space can be filled with fluids including gas or water in silage (Mohsenin, 1980). Porosity was measured with a special apparatus, which was designed by Kocabiyik et al. (2004). Porosity measurement apparatus was shown schematically in Fig. 2.

This apparatus consisted of two steel chambers with the same volume. These chambers had the same axis and were separated by a divider to prevent volume contact. The connection of the two chambers was done by welding. One of the chambers was connected to the silage silo by a valve. A manometer and a valve were added to the apparatus to control pressured air between the chambers and to determine the air pressure value (Kocabiyik et al., 2004).

For the measurement of porosity, first, chamber of the measurement apparatus was filled with pressured air. Desired air pressure was adjusted by a manometer and a valve, which was located at the pressure air inlet. After chopped materials were filled into experimental silo, the lid of the mini silo was closed leak proof. Then the valve between the chambers and the mini silo was opened and the filling of air in pressured air chambers to the voids among the silage in the mini silo was supplied. Decrease in pressure of the pressured air that filled the voids among the silage in mini silo was obtained by reading the manometer. Then porosity values according to ideal gas law were calculated using the pressure values obtained (Kocabiyik et al., 2004). According to ideal gas law:

(2)

(3)

where:

Index of 2 for the same values represents values in mini silo. Total air Mass in apparatus (M) is air mass in pressured air chamber (M₁) and air mass in mini silo (M₂).

(4)

(5)

(6)

As shown in Eq. 6, porosity ratio (_) is the rate of volume in mini silo to the volume in pressured air chamber. In tests, first measured pressure value was fixed at 1.3 kg cm^-2.

Determination of permeability: Permeability was determined by means of passing 1 L water into the ensiled material in the mini silos. Permeability was measured by reading the time period of the water that was drained from the silo. Permeability was calculated according to Darcy law as follows:

(7)

(8)

where:

The experiment was organized in a 3 (stages of maturity; BA (beginning of Anthesis), ML (one-third Milkline), BL (Blackline) x 5 (compaction treatments; NC, WV, C₁, C₂ and C₃) factorial arrangement of treatment. Each treatment combination was replicated 4 times. Data was evaluated by MSTAT statistics program.

RESULTS AND DISCUSSION

Density: The densities of the sunflower silages harvested at the three maturity stages and under five different ensile applications (without compaction, vacuum and three compaction levels) were given shown in Fig. 3.

The differences among maturity stages and ensile applications in density were found to be significant (F** = 3.92 for maturity stages and F** = 14.32 for ensile applications). Muck et al. (2004) found that density was affected by pressure and moisture content, but not by time of compaction. The density of the samples ranged from 572-1085 kg m^-3. The highest densities observed at the BL stage and under C₃ application, the lowest densities at the BA stage and under NC application. Similar results were also found by Roy et al. (2001). They stated that pressure had a significant effect in increasing the density and moisture. In the highest densities found low porosity values as shown by Rees et al. (1983) and Savoie et al. (2003).

Porosity: Porosity of the sunflower silages investigated at the three maturity stage levels and five different ensile applications were shown in Fig. 4. Changing porosity according to maturity stages and ensile applications were found to be statistically significant (F** = 32.34 for maturity stages and F** = 100.23 for ensile applications).

The porosity value of the silages was increased at maturity stage, but decreased with increasing compaction values. The highest porosity value (57%) was at the BL stage and under NC application. This was supported by the results of Williams (1994), who found low moisture content results in a higher porosity of the conserved forage. The lowest porosity value (15%) was at the BA stage and under C₃ application. Peterson (1988) studied on corn ensiling and found that porosity values as from 43-38% according to maturity.

Fig. 3:	Density of sunflower silages at three maturity stages and five different ensile applications

Fig. 4:	Porosity of the sunflower silages at the three maturity stages and under five different ensile applications

Fig. 5:	Permeability of the sunflower silages at the three maturity stages and under five different ensile applications

Like this study, Roy et al. (2001) explained that the low porosity could be achieved by increasing compacting.

Permeability: The permeability of the sunflower silages harvested at the three maturity stages and five different ensile applications were shown in Fig. 5. Permeability showed significant variations at maturity stages (F** = 7.63) and under ensile applications (F** = 14.95). The highest permeability (0.0488 cm min^-1) was observed at the BL stage and under NC application. The lowest permeability (0.0072 cm min^-1) was observed at the BA stage and under WN application. Montross and McNeill (2005) found that the permeability value of the silages showed variation according to moisture content (maturity stage), which was similar to that of this study.

Correlation between density, porosity and permeability of the sunflower silage investigated at the three maturity stage levels and under five different ensile applications were shown in Table 1. The correlation between density and permeability was not found to be important, whereas the figure was significantly important between the density and porosity (0.707**). It can be explained that pore inside silage was diminished by applying compaction. Holmes and Muck (2007) also determined porosity is most influenced by density.

Table 1:	Correlation of density, porosity and permeability of sunflower silage
**Significant at p<0.05, NS: Not Significant

Permeability increased with increasing porosity and decreasing density, but the relationship between permeability and moisture content is complex as mentioned by Williams (1994). There was significant linear correlation between permeability and porosity (0.665**), since, pore helped water pass quickly inside silage.

CONCLUSION

The results of this study revealed that maturity stages and ensile applications had important effects on the density, porosity and permeability values. The density of sunflower silage was influenced by maturity stages and ensile applications. At the stage of the maturity, the densities changed, due to the higher DM concentrations plants matured. The porosity values of the sunflower silage increased at different maturity stages, but decreased with increasing compaction values. Permeability decreased when compaction levels were increased. The higher permeability values were observed at the lowest moisture content. Whole crop sunflower can be used to ensile, but the ensiling and nutritional quality depends upon the stage of maturity at the time of harvest. The relationship between permeability and porosity highly significant.

ACKNOWLEDGEMENT

This study was supported by Turkya University scientific research project fund under the project number TUBAP 587.