LESSON 7. Design and construction of Fodder Silo

1 Introduction

It is need to store animal fodder and feeds, fertilizers, seeds, vegetables, milk and milk products, farm machineries etc., in a variety of storage structures.

1.1 The Silo

Silo is a farm structure which stores and products the animal fodder providing an ideal condition. The fodder is cut and packed in the silo in an air tight condition to favor for partial fermentation. The stored fodder is known is known as silage. Silage can be made from any green crop with moderately tough stalk. e.g. Grass, Sugarcane, legumes, etc.

Silage is more nutritive then dries stalk. But when compared to green fodder, there is some loss of nutritive value in silage, because the sugar is converted into lactic acid giving a sour taste. Losses are also occurring due to surface spoilage, fermentation and seepage. Loading of tower silos is difficult. It heeds a mechanical loader or a large capacity blower for elevating the cut fodder. The wall should be smooth, circular and strong enough to avoid cracking due to lateral pressure. Hence, a heavy reinforcement is a must.

The only advantage is if the water table is very close to the ground level, tower silos are preferred. The cost of constructing these silos is comparatively much higher than that of horizontal types.

1.2 Horizontal silos

Horizontal surface silos are really used for storing silage. These silos are readily and cheaper made at any time and they can be easily filled and unloaded without any equipment. They are successful in areas having a deep water tale. The dry matter losses ranges from 20-30% while filling either trench or pit site. Chopped silage should be spread, leveled and packed. They are filled, till the silage reaches the above G.L. They should be covers with dry paddy straw or plastic covers. Well packed silage weighs 480-800 g per m3. Area=650 kg/m3.

1.2.1 Pit silos

It is a circular deep well which is lined all along the side and bottom to prevent the water entering it. They can be made of bricks or stores or concrete with either lime or cement. Up to a depth of 15m a 22.5m wall is provided with plastering the entire inner surface. A simple roof over the silo can be provided to protect the silage from sun and rain. Generally a cow is feed about 1.4kg of silage per 45kg of her body weight per day. i.e. 1.4 kg/45 kg /day or 3 kg/100 kg of body weight.

Diameter of the silo is determined by the quantity of silage feed daily. The rate removal should at the rate of 10cm/day. The diameter is limited to 6 m and its depth is kept 2-3 times the diameter.

Design criteria  

    1. Rate of removal          -      10 cm/day
    2. Silage fed per day       -       3 kg/100kg of body weight
    3. Maximum diameter     -       6 m
    4. Depth                        -       2-3 times diameter
    5. 1m3 of silage              -       650 kg

Problem: Work out the economical diameter and depth of a silo to store  sufficient quantity of silage  for a herd of 300 dairy cows having an average body weight of 450 kg each. The cows fed with silage for 200 days /year.

Given :

No. cows                  -  300

Body weight             -  450 kg

No of days per year   -  200 days /year.


Let i) 1m3 of silage = 650kg.

     ii) Thickness of silage fed per day  = 10 cm/day.

    iii) Let each cow I fed 3kg of silage per 100 kg of the body weight.

Weight of silage required for each cow = (3/100) X 450

                                                              = 13.5 kg / day

Weight of silage required for 300 cows   =13.5 X 300

                                                                 = 4050 kg / day

Volume of silage required to be stored   =4050/650

                                                          = 6.23 m3                               -------------------  (1)

Allowing 20 % loss, Actual volume of silage = 6.23 + 0.2x6.23  = 7.476 m3

Volume of pit for a daily withdrawal depth of 10 cm =      Lesson 8 1     -------------- (2)

Equating (1) & (2)        Lesson 8 2= 7.476

                                                Lesson 8 3

Depth of the silo   =  daily depth x no. of days  =  0.1 x 200  =  20 m

1.2.2 Trench silos

It can be either lined one or unlined one. Unlined silo is easy to construct but give more spoilage of silage and caving in of sides due to rain. A lined trench silo is advantageous and the lining can be made with brick concrete or cement plaster with reinforcing wire mesh. Filling packing and sealing are similar to pit silo. The drainage water should not be allowed to collect near the trench and so drains should be made around the trench. The cross section depends on number of animals to be fed and the length is determined by the number of days, the silage is fed in a year.

Problem: Design a trench silo for a small farm having 140 buffaloes weighing 680 kg each and has to be fed at the rate of 4 kg/100 kg of its weight. The silage is fed 160 days in a year.

Given Data:

            No. of animals             = 140

            Wt. of each animal       = 680 kg

            Feeding rate                 = 4 kg / 100 kg of body weight

            No. of days of feeding  = 160 days


            Let the depth of silo be 2.5 m

            Length of feed per day be 15 cm

            Side Slope be 1 : 2

 Lesson 8 4

Equating (1) & (2)

Lesson 8 5


            Top width of silo         = 16.87 m

            Bottom width of silo    = 14.37 m

            Depth of silo               = 24.0 m

            Length of silo              = 28.8 m.        

Last modified: Friday, 7 February 2014, 8:42 AM