Fodder

Lessons

Senior 3 · Agriculture

Fodder

3 lessons

Lesson 3 of 3

Growing, Harvesting and Conserving Fodder Crops

25 min

Let's begin

In April, Napier grass grows so fast that a farmer cannot cut it all, and it turns into tall, woody canes that cows refuse. In August, the same plot is dry and short, and the cows go hungry. Good fodder farming solves both problems at once: grow the right crop for the land, cut it at the right stage, and store the surplus of the rains as hay or silage for the dry season. This lesson covers the cultural practices for the fodder crops named in your syllabus, then how fodder is harvested, fed and conserved.

Definition

Cutting interval: the time between two cuts of a perennial fodder grass.

Stubble height: the height of the stems left after cutting, from which the grass regrows.

Chaff cutter: a hand or motor machine that chops fodder into short pieces, so that animals waste less.

Prussic acid (hydrogen cyanide, HCN): a poison released from compounds in young or stressed sorghum plants; it can kill cattle within minutes.

Ensiling: storing chopped green fodder airtight so that bacteria turn its sugars into acids, which preserve it as silage.

1. Cultural practices for six fodder crops

Crop	Where it suits	Establishment	Care	Harvest and use
Guatemala grass (Tripsacum andersonii), perennial	medium and high altitudes; tolerates acid, less fertile soils better than Napier	root splits or cane cuttings, about 1 m by 0.5 m, at the start of the rains (it sets almost no viable seed)	weed until the canopy closes; manure or compost after every cut; fill gaps	cut when about 1 m tall, leaving 10 to 15 cm of stubble; chop and feed fresh
Para grass (Urochloa mutica), perennial	wet, waterlogged valley bottoms and stream banks, where most grasses fail	runner cuttings with 3 or 4 nodes, pressed into moist soil about 50 cm apart	spreads fast by runners; keep it out of crop fields and drainage channels	cut every 6 to 8 weeks, or graze lightly; feed fresh
Fodder maize, annual	most areas below the coldest highlands	certified seed, planted closer than grain maize (for example 75 cm by 15 to 20 cm)	as for grain maize (Unit 2): basal and top-dressed fertiliser, two weedings	green feed from tasselling; for silage, cut whole plants when the grain is at the dough stage
Fodder sorghum, annual (some varieties regrow)	warm, drier areas	seed drilled in rows closer than grain sorghum	weeding; nitrogen fertiliser; cut regrowth again where the variety allows	cut at boot to early heading; never feed young or drought-stressed plants fresh (prussic acid)
Oats, annual	cool highlands	seed drilled 20 to 30 cm apart, about 80 to 100 kg ha⁻¹; often sown with vetch, a legume	one early weeding; nitrogen fertiliser	cut at boot to early milk stage for green feed or hay
Millet (pearl millet), annual	hot, dry areas and light soils	seed drilled in rows	weeding; regrows after cutting	cut before flowering for leafy green feed; several cuts a season

2. Cutting and feeding

Cut at the right stage. Young fodder is leafy and rich in protein but gives little bulk; old fodder gives more bulk, but it is stemmy, low in protein and hard to digest, and animals waste much of it. Napier is best cut when about 1 m tall, every 6 to 8 weeks in the rains, leaving 5 to 10 cm of stubble.
Feed back the soil. Every cut removes nutrients, so return manure or slurry after each cut, or yields fall year by year.
Chop fodder into pieces 2 to 5 cm long with a chaff cutter or machete: animals eat stems as well as leaves, and less is trampled.
Balance the diet with legumes or fodder-tree leaves. Keep leucaena to no more than about a third of the diet, because its leaves contain a toxin, mimosine.

3. Conserving fodder for the dry season

Hay. Cut grass or oats at early flowering, when the yield of leaf and the protein content are both good. Spread it in the sun and turn it until it is dry enough to store (about 15% moisture: the stems snap rather than bend). Store it off the ground in a dry, airy shed. Rain on drying hay washes out nutrients and causes mould.

Silage keeps green fodder moist and nutritious. It is made from crops rich in sugar, such as fodder maize and sorghum, or from Napier with molasses added, in a pit, a trench, or strong polythene bags (Figure 8). Bacteria that need no air turn the sugars into lactic acid, and the acid stops rotting. Air spoils silage, so compacting and sealing are the key steps.

Figure 8. The steps of silage making.

Worked example 1: what does drying do to hay?

Problem. A farmer cuts 500 kg of fresh oats at 80% moisture and dries it to hay at 15% moisture. What mass of hay does he get?

Solution. Drying removes only water; the dry matter stays the same.

Dry matter $= (1 - 0.80) \times 500 = 100\,\mathrm{kg}$ .
In the hay, dry matter is 85% of the mass, so hay $= \frac{100}{0.85} \approx 117.6\,\mathrm{kg}$ .

Answer: about 118 kg of hay; about 382 kg of water has dried off.

Worked example 2: sizing a silage pit

Problem. A farmer wants silage for 3 cows, 25 kg per cow per day, for a 90-day dry season. Well-packed silage weighs about 600 kg per cubic metre (illustrative). How big must the pit be?

Solution.

Silage needed $= 3 \times 25 \times 90 = 6\,750\,\mathrm{kg}$ .
Volume $= \frac{6\,750}{600} = 11.25\,\mathrm{m^3}$ .
A pit 5 m long, 1.5 m wide and 1.5 m deep holds $5 \times 1.5 \times 1.5 = 11.25\,\mathrm{m^3}$ .

Answer: 11.25 m³, for example 5 m by 1.5 m by 1.5 m. Some silage is always lost at the surface and edges, so make it a little larger.

Warning

Safety

Prussic acid: do not graze or feed fresh sorghum that is young, regrowing after a cut, or wilted by drought or frost. Cut it at the right stage, and wilt or ensile it before feeding. Poisoned animals breathe fast and may collapse: call a veterinarian at once.
Mouldy feed: never feed mouldy hay or silage; moulds can make animals ill and cause abortion.
Chaff cutters cut fingers as easily as grass: feed the fodder in with a stick, never with hands near the blades, and never let children operate one.

Tip

Exam technique: for "describe the cultural practices of crop X", write in order: where it suits → land preparation → planting material and spacing → weeding and manuring → harvest stage and use, with one reason for each step.

Access Agriculture: "Silage from maize (Summary)". Match each step you see with the six steps in Figure 8, and note how the farmers press out the air.

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Practice

Which fodder grass suits waterlogged valley bottoms? How is it planted?
State the harvest stage of: (a) fodder maize for silage, (b) oats for hay, (c) Napier for fresh feeding.
Explain why young or drought-stressed sorghum must not be fed fresh.
Explain why fodder cut too late is poor feed, and why fodder cut too early gives a low yield.
300 kg of fresh grass at 75% moisture is dried to hay at 15% moisture. Calculate the mass of hay.
List, in order, the steps of making silage, and say why compacting and sealing are essential.
Two cows will each eat 30 kg of silage a day for 120 days. If packed silage weighs 600 kg per m³, what volume of silage is needed?
A farmer opens his silage pit and finds black, slimy silage that smells rotten. He plans to feed it anyway "so it is not wasted". Evaluate his plan and say what went wrong.

Show answersHide answers

Para grass. Plant runner (stolon) cuttings with 3 or 4 nodes, pressed into moist soil about 50 cm apart, with some nodes covered.
(a) when the grain is at the dough stage; (b) at early flowering (between boot and early milk stage); (c) when about 1 m tall, every 6 to 8 weeks in the rains.
Young, regrowing and stressed sorghum releases prussic acid (hydrogen cyanide), which can kill cattle within minutes.
Late-cut fodder is stemmy, low in protein and hard to digest, and much is wasted; early-cut fodder is nutritious but has had too little time to grow, so the yield of dry matter is low.
Dry matter $= 0.25 \times 300 = 75\,\mathrm{kg}$ ; hay $= \frac{75}{0.85} \approx 88.2\,\mathrm{kg}$ .
Cut at the right stage; wilt and chop; fill in thin layers and tread firm; seal airtight; leave to ferment for at least 3 weeks; open one end, take daily and reseal. Air lets moulds and rotting bacteria grow, so air must be pressed out and kept out for the lactic-acid fermentation to preserve the fodder.
Silage $= 2 \times 30 \times 120 = 7\,200\,\mathrm{kg}$ ; volume $= \frac{7\,200}{600} = 12\,\mathrm{m^3}$ .
He must not feed it: spoiled, mouldy silage can make animals ill and cause abortion. Air probably got in, through poor compaction, a torn or badly weighted cover, or leaving the pit open, or the fodder was too wet or too low in sugar (no molasses). He should discard it and improve compaction and sealing next time.

Key points

Match the crop to the land: Guatemala grass on poorer and acid soils, para grass in wet valley bottoms, oats in the highlands, sorghum and millet in dry areas, fodder maize for silage.
Cut at the right stage, return manure after each cut, chop fodder, and balance grass with legumes.
Conserve the surplus of the rains as hay (dry to about 15% moisture) or silage (chopped, compacted, sealed airtight); never feed mouldy feed or young sorghum fresh.

11. Cultural practices for six fodder crops

22. Cutting and feeding

33. Conserving fodder for the dry season

1. Cultural practices for six fodder crops

2. Cutting and feeding

3. Conserving fodder for the dry season