Effects of raw material and silo size on silage quality

M Kızılsimsek, A Erol and S Calıslar^*

KSU Agriculture Faculty, Field Crops Department,
Kahramanmaras,Turkey
mkizil@ksu.edu.tr
*KSU Agriculture Faculty, Animal Science Department,
Kahramanmaras,Turkey

Abstract

Oat (Avena sativa L.), barley (Hordeum vulgare L.), triticale (X. triticosecale Wittm.), and vetch (Viciasativa L.) were used as winter crops in the first experiment and maize (Zea mays L.), sorghum (Sorghum bicolor (L) Moench.), alfalfa (Medicagosativa L.) and soybean (Glicinemax L.) were used as spring crops in the second experiment. Each raw material was ensiled separately and as mixtures in laboratory scale silo (LSS) and big scale silo (BSS) with loading capacities of 10 kg and 3 tonnes of fresh material, respectively. The study was carried out for two years during 1999-2001. Plants were grown in the field and plots were arranged as mixtures of species and pure stands. Silos were opened 45 days after ensiling. The resultant silages were evaluated in terms of physical (colour, smell and structure) and chemical (pH, acetic acid, butyric acid and crude protein) properties.

Silo type had a significant effect on chemical and physical characteristic of  the resultant silage. High environmental temperature decreased the activities of acetic acid bacteria. It was also found that addition of legumes into silage mixtures increased the crude protein (CP) content in both experiments. Although there were considerable differences in pH and acetic acid production in LSS and BSS, the transferability of data from LSS to BSS seems to be feasible. 

Keywords: forage crops, konigsberg scores, mixture, silage.

Introduction

Although forages are very important in ruminant nutrition, the production of quality forage is not always sufficient to meet nutrition requirements. The area allocated for forage production in Turkey s equivalent to 2.4 % of total agricultural land which is ten times lower than the required proportion . Although grasslands occupy approximately 1/3 of the total surface area of Turkey, a great majority of them are in poor conditions due to misuse such as overgrazing and early grazing for centuries. This shows how great is the deficit of forage production in the country (Kılıç 1997). Therefore, animal production and the consumption of animal products are very low compared to developed countries. Animal production will increase if the factors such as genotype improvement, animal health and feed production are managed properly (Sağlamtimur et al 1995). However, most of the researchers have reported that the main problem in animal production in Turkey is related to nutrition. Gokkuş et al (2000) recommended that small ruminant animals should not be grown in the places where the land is insufficient for grazing.

Ensiling is one of the most efficient, cheapest and safest ways for conserving forage. The key point for best quality silage is to make a good balance between carbohydrate and protein content in the raw material. This balance can be obtained by ensiling cereal and legumes together. In this way, sufficient fermentable carbohydrates for lactic acid bacteria are provided (Koljajic et al. 1998) and simultaneously the protein content of silage is increased (Koljajic et al 1998; Asefa and Ledin 2001; Nayigihugu et al 2002). In addition, mixing legumes and grasses increases biomass yield, CP content, nutritive value of resultant silage and soil fertility (Martin et al 1998; Assefa and Ledin 2001; Nayigihugu et al 2002).

Oat, triticale, barley, and vetch are important crops, which are able to be grown during winter in Turkey. Maize, sorghum, soybean and alfalfa can successfully be grown as second crops in irrigated areas in Turkey. Although many researches have been done to develop procedures of making high quality silage in many parts of the world, studies devoted to silage production are very limited in Turkey. Moreover, most of the silage experiments have been carried out in laboratory scale silos (LSS), and there has not been mentioned the transferability of the results to big scale silos (BSS). LSS are generally kept at the room temperature but BSS are under varying conditions determined by location and season.

The main aims of the study were (i) to compare ensiling effects of legume - grass mixtures with single crops; (ii) to determine the possible effects of silo type on silage quality, and (iii) to evaluate the transferability of the results of LSS to BSS.

Materials and methods

Field studies

Field and laboratory studies in this research were conducted in 1999-2001. Barley, triticale, oat and vetch (first experiment),  and maize, sorghum, alfalfa and soybean (second experiment) were used as raw materials for silage. Applications were pure oat (PO), oat+vetch (OV), triticale+vetch (TV) and barley+vetch (BV) mixtures for the first experiment and pure maize (PM), pure sorghum (PS), maize+alfalfa (MA), maize+soybean (MS), and sorghum+soybean (SS) mixtures for the second experiment. A completely randomised plot design with three replications was used for two years. Plants were grown as mixtures, except for MA mixture, and in pure stands in field trials. Maize and alfalfa were grown on separate plots and mixed just before ensiling because of the multi-cut characteristic of alfalfa. Although in the first experiment seeding rates of legumes were 50% in all mixtures, the vetch rates at harvest were 45.3%, 41.8% and 43.0% in the mixtures of OV, TV and BV, respectively. Soybean rates for MS and SS in the second experiment were 39%. Alfalfa rates in mixtures were designed as 45% since it was cut separately. Winter plants were sown in October and summer plants were sown as second crops at the end of June, immediately after harvesting wheat. Crops in mixture systems were cut and chopped together by the time cereals were at the milk stage and legumes were at the beginning of flowering. Winter and spring crops were harvested in the middle of April and at the end of September, respectively. Dry matter (DM) contents of raw materials at harvest were 28.9, 30.8, 30.5 and 30.4 g kg^-1 for PO, OV, TV and BV in the first experiment, and 30.5, 30.8, 29.4, 27.7 and 28.9 g kg^-1for PM, PS, MA, MS and SS in the second experiment, respectively.

Preparing silages

All samples were ensiled in 3 replications in both LSS and BSS, with loading capacities of 10 kg and 3 tonnes of fresh forage with 30% DM, respectively. Plastic containers providing anaerobic conditions were used as LSS. Bricks were used as a wall material of BSS to provide similar conditions to the farmers' outdoor clamp silo. Both winter and spring silage crop materials were chopped approximately at the size of 1 cm, theoretical cut with a conventional silage track machine and loaded into silos. Each silo was loaded with a packing density of 200±5 kg DM m^-3 and sealed immediately (Taylor et al 2002). BSS were kept completely under on-farm conditions with an environment temperature of 28-39 ºC for the first experiment (from middle April to early July) and 25-34 ºC for in the second experiment (from late of September to middle of October). LSS were kept at room conditions (22-25 C) for all treatments. Silos were opened 45 days after ensiling (Tansı et al 1997).

Physical and chemical analysis

When the silos were opened, the silage at the surface was removed. 50 g sub-samples from 3 different points in LSS and from 5 different points in BSS were collected and mixed. These samples were used for all physical and chemical analysis. Physical characters were scored by using 1-4 scale for colour, 1-7 scale for smell and 1-4 scale for structure analysis, which is an indication of the situation of plant organs such as leaf and stem in resultant silages.

Water extracts from samples were filtered through Whatman 54 filter paper. Butyric and acetic acids were analysed by gas chromatography (Taylor et al 2002). Crude protein (CP) was determined using the Kjehldahl method (AOAC 1984). In order to determine the quality classes of silages, all the investigated physical and chemical characters were scored according to the Konigsberg Key as exactly described by Bulgurlu and Ergul (1993). Konigsberg scales for physical and chemical characters are given in Table 1.

As a result of the general evaluation, the quality classes of the silages were ranked as Very Good (VG), Good (G), Moderate (M), Poor (P) and Very Poor (VP) with the given total points ranges 32-35, 28-31, 24-27, 18-23 and <18 respectively.

Statistical analysis

The results were subjected to analysis of variance to compare mean differences among silage raw materials and between silo types by using the SAS statistical programme. Least Significant Difference (LSD) test was applied in order to determine the statistically different groups.

Results

The physical characteristics of silages

There were significant differences between silages in terms of colour and smelling characteristics (Table 2). OV mixtures among winter crops always gave the highest colour, smell and structure scores on the average and were followed by PO. SS mixtures among spring crops yielded the highest colour and structure scores compared to other raw materials.

The silo type had a significant effect on silage structure in the first experiment whereas it affected the colour of silage in the second experiment. Moreover, silo type also affected smell scores in both spring and winter crops. Smell scores were higher in BSS than in LSS for all treatments.

Chemical composition

As indicated by low pH values, all silages were well preserved. Differences between crop materials in terms of pH and CP values were found to be significant (Table 3).

In the first experiment, the lowest mean values related to pH and acetic acid were in PO silages and the best butyric acid mean value was found in the OV mixture. In the second experiment, differences between raw materials in terms of pH and butyric acid were statistically important. In the two experiments CP contents were significantly affected by raw materials used for ensiling. The highest protein content was obtained from the TV mixture, followed by the OV mixture with an insignificant difference because of higher protein content of triticale compared to that of other cereals.

Comparisons of results by Konigsberg key

Konigsberg scores of silages for the first experiment and the second experiment are given in Table 4. OV mixtures resulted in the best quality of silages both in LSS and BSS due to low pH and higher scores of physical characters. On the other hand, TV and BV silages gave moderate or poor quality silage because of high pH and lower physical characters scores. For the second experiment, silage quality classes were better in BSS than LSS, especially due to high pH and acetic acid scores in BSS in all treatments. This indicates that silages in BSS were better fermented than in LSS.

Discussion

Scores related to physical parameters of mixtures (Table 2) were found higher than those of sole crops silages. This result is in agreement with the finding of  Türemiş et al (1997). The OV mixture among winter crops and SS mixture among spring crops gave higher total scores of physical parameters than the other treatments in BSS or LSS. Scores of physical parameters were possibly affected by chemical components, especially by pH.

Quality classes of silages (Table 4) according to total scores were higher in BSS than in LSS. These differences were especially due to low pH values and low acetic acid production (Table 3) resulting in high acetic acid scores (Table 4) in BSS that was designed in outdoor, completely on-farm conditions with a mean environment temperature of 28-39 ºC for the first experiment and 25-34 ºC for the second experiment during ensiling. Since BSS has lower pH and acetic acid values compared to LSS, then silage quality was positively affected. In BSS, internal temperature of silage was expected to be higher than that of LSS because of environmental conditions. High temperature might be a reason for lactic acid bacteria (LAB) to grow well because of their tolerance to the elevated temperatures (Oshima et al 1997). This fact suggests that undesirable microorganism activities were slowed down by high temperature and low pH. Türemiş et al (1997) reported that acetic acid production is generally inhibited by low pH. It was also reported that acetic acid contents of silages were rather negatively affected by increasing environment temperature from 20 to 40 ºC (Ohshima et al 1997).

The effect of temperature on LAB might have occurred at the early stage of the fermentation process depending on decreasing speed of pH value (Ohshima et al 1997). It was reported that counts of coliform bacteria were greater in high pH silage than low pH silage (Seale et al 1986.

The TV mixture gave the highest CP content compared to other cereals as a simple reflection of the raw materials in the first experiment. It has been reported that triticale has higher protein content and can give higher quality silages when mixed with barley (Kenelly and Khorsani 1998). It has also been mentioned that mixtures of cereals with legumes had higher CP content than that of cereals grown as a sole crop (Assefa and Ledin 2001) due to high CP content of legumes.

Silo sizes had a significant effect on both pH and acetic acid in the first and second experiment, and on butyric acid only in the second experiment. CP content of silages was not affected by silo size.  Acetic acid and butyric acid concentrations are strictly depending on pH values in silages (Turemis et al 1997). Mixing cereals and legumes was found to be advantageous in increasing forage quality  with CP content at the rates of 28% and 15% for the first experiment and the second experiment, respectively (Table 3). The mixtures had also significantly higher CP in both experiments compared to cereals alone, again as a reflection of the raw materials used.

Conclusions

• Silo type had a considerable effect on the chemical and physical characteristic of the esultant silage. 

• It was also found that adding legumes into silage mixtures increased the CP content.

• The transferability of data from small scale (LSS) to large scale (BSS) seems to be possible although there were considerable differences in pH and acetic acid production in LSS and BSS.

Acknowledgements

This study was supported by the Turkish Scientific and Technical Research Organisation (TUBITAK)

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