Major field crops, especially cereals, produce large quantities of stem and leaf in addition to their saleable product, which is usually seed. The straw or stover is usually over half the harvestable vegetation of the crop. Such coarse roughages cannot be eaten by humans, but they can be transformed into economic products by livestock. Some cereals and pulse crops are also grown specifically for hay, and details of their cultivation as forage are given in Chapters III to VI.
Our subject here is the residues of field crops that are grown for purposes other than fodder. While these residues are coarse roughages, they are often no worse than, and possibly better than, dried, mature, tropical grasses. This should be kept in mind when dealing with small-scale agriculture in tropical systems: better straw harvesting and storage, with possibly urea treatment, may be cheaper and more productive than going to great trouble to harvest bush hay. Details of the feeding value of some residues are given later, in Chapter X.
Straw is the stems and leaves of small cereals; chaff is husks and glumes of seed removed during threshing (chaff is usually a richer feed than straw, but more difficult to feed because of awns, etc.). Modern combine-harvesters generally deliver straw and chaff together; other threshing equipment separates them. Stover is the field residues of large cereals, such as maize and sorghum. The leaves and stems of pulses are variously described as haulms or vines. Stubble is the stumps of the reaped crop, left in the field after harvest. Agro-industrial wastes are by-products of the primary processing of crops, including brans, milling offal, dal polishings, press-cakes and molasses. These are mostly concentrate or near concentrate feeds, but since they depend on processing rather than crop production, they are beyond the scope of this book. Brans from on-farm husking of cereals and pulses are fed to livestock or foraged directly by backyard fowls.
Straws and stovers have always been an important part of agriculture. Until the advent of cheap inorganic fertilizers and mechanization, they were an integral part of large-scale farming as feed for draught and other stock and litter for the production of manure, which was essential to the maintenance of fertility. At the small-scale farming and subsistence levels, agricultural residues have retained their importance, indeed, the importance is growing because of the ever-decreasing access to free grazing as cropping area expands. With changing production technologies in mechanized agriculture, straws were for some time thought to be of so little value that they were often burnt in the field. Environmental legislation, and the development of straw treatment to improve digestibility, has brought an end to straw burning in most developed countries, where it is now either fed to livestock or used for industrial purposes.
The change of land use from grazing to cereal production does not usually reduce the amount of roughage available for livestock, as the amount of straw and stover will be as great or more than the natural herbage previously on offer. In the vast irrigated lands which have been developed in arid and semi-arid areas (e.g., Asia, Egypt, Sudan) the amount of roughage from crops is vastly greater than the former production from natural grassland. Rice-based production systems yield large amounts of straw. Frequently, the change from extensive grazing to arable or mixed farming leads to an increase in the number of livestock kept. Many agricultural production systems are mixed, with both cropping and livestock, often multipurpose; with decreasing grazing availability, the stock rely on crop residues as the basis for their nutrition. It is essential, therefore, that these residues be used to their best advantage and are stored correctly so that the livestock have an adequate supply throughout the year. Since crop residues in themselves do not constitute an adequate ration for production or for young stock, complementation by high quality green fodder, and sometimes concentrates, must usually be foreseen.
The ease of harvesting and drying residues depends, of course, on the climate. In sub-humid and drier climates and in temperate regions there are usually few problems with straw harvesting. In the humid tropics and subtropics, however, the weather at harvest time may be such that it is difficult, if not impossible, to conserve straw, and especially legume haulms, in good condition. Groundnut tops harvested under hot dry conditions, for example, are an excellent feed, but where the harvest is under moister conditions the tops usually become a blackened, diseased mass before they can be dried. The proper drying of rice straw during the rainy season and on wet land is difficult, if not impossible, especially when there are many other demands on labour.
Stubbles are frequently grazed once the crop is removed, They often contain, in addition to the bases of the cereals and some straw, valuable feed in the form of grain which has been lost in the harvesting process, especially after mechanical harvesting, and weeds. Some methods of grain harvesting leave the plant standing after the heads or cobs have been removed by hand; this is common with small-scale farm systems for rice, maize, bulrush millet, finger millet and sorghum. Where feed is plentiful or where labour is scarce, these residues may be grazed in situ. This is advantageous for the livestock at the time, in that it allows them to graze selectively and probably find at least a maintenance diet from what might be a sub-maintenance feed if taken as a whole. It does, however, lead to a lot of wastage through trampling. Where there is an overall shortage of roughage for the dry season or winter it is preferable to harvest, dry and store as much of the crop residues as are necessary to assure the farm's roughage needs through the lean season.
Traditional ways of organizing grazing of crop residues may develop where specialized agricultural and stock-rearing communities are in the same area, such as the interaction of the Fulani herds in West Africa with several settled agricultural groups. Stubble grazing rights may be given to the herders (with or without payment) to the mutual benefit of both communities: the livestock eat the stover and also recycle fertility to the arable land; the herds are often kraaled on specified fields at night to build up their fertility. Recently, especially in drought periods, however, there has been a move towards harvesting the stover and selling it to passing herds.
In North Africa, transhumant flock-masters (who graze their herds from the desert fringe to the more northerly agricultural lands, according to season) buy stubble and fallow grazing in the crop-producing, higher rainfall areas to feed their herds through spring and summer. The shepherds are skilled in estimating the amount of grazeable forage on any given piece of land and in finding a succession of fields to see them through the season.
Crop residues in soil conservation
The great role of stubble in protecting soil against both hydraulic and aeolian erosion is well known. Stubble-mulching allied to minimum tillage is a well-established technique for protecting soil and conserving moisture in large-scale farming in cold semi-arid regions. Stover left on the field will also protect the soil, and cutting crops like maize and sorghum well above soil level can provide useful protection to the soil. In small-scale farm systems, however, straw and stover are often so greatly sought after as feed, thatch, bedding and fuel that crops are frequently cut to ground level, and maize roots may be dug out and dried as fuel.
Competing uses
Straws, stovers and chaff have many uses other than as animal feed within the farm economy, and these must be taken into account when assessing availability and profitability in livestock feeding systems. Within livestock production systems, straw is also used as litter and bedding (providing farmyard manure or compost), and chopped wheat straw is locally much in demand as poultry litter. Straw, especially rice straw, is often purchased by paper factories; straw is also widely sold for use as packing materials; straw and rice husk is widely used in semi-artisanal brick manufacture; chopped straw mixed with mud is used for plastering, both internally and (in hot, dry climates) externally; the strong stems of maize, sorghum and bulrush millet are used in traditional building, screens and grain stores; long straw is used as thatch; and straws and stovers are used as fuel in areas of scarcity, alone or chopped and mixed into dung cakes.
The proportion of straw, or stover, to grain varies from crop to crop and according to yield level (very low grain yields have a higher proportion of straw - the ratio is infinite when a crop fails through drought) but is usually slightly over half the harvestable biomass. The height of cutting will also affect how much stubble is left in the field: many combine-harvested crops are cut high; crops on small-scale farms where straw is scarce may be cut at ground level by sickle or uprooted by hand, as is common on the Loess Plateau.
Rice straw
This is one of the most important cereals in the world, and especially so in Asia. Much is grown under small-scale farm conditions, with the straw widely used as a feed for work and milch stock. Methods of harvest vary. Often, in small-scale farm systems, either the heads or the whole crop is cut by sickle; frequently the crop will be cut while still in standing water because of the weather or lack of water control. The grain is then threshed out by beating on a rack or stone, or by using a small thresher. Mechanized rice production is usual in areas where combine-harvesters can be used. Rice straw is unusual in that the stem is more digestible than the leaves, the opposite of other cereals. For livestock feeding, it is therefore advantageous to cut it as close to the ground as possible. With hand harvesting, the crop is often cut when the straw is still relatively green. This will produce a higher quality straw for feeding than from mature plants. When only the heads are harvested the straw should be cut as soon as possible after the heads are removed (if labour is available), and dried to conserve its quality as a feed.
Figure 36. Rice straw stacked by a homestead in Nepal; the tree leaves are supplementary green feed
Drying rice straw is often a problem in high-rainfall areas because double-cropping means that at least one harvest is under very wet conditions. With the pressure of work at threshing time, it is difficult to ensure adequate care in spreading out the threshed straw to dry, and so a poor, mouldy product is often the result. Wherever possible, rice straw should be dried (on bunds and dry areas) as soon as possible after threshing in order to ensure the best possible straw for livestock feed. In high rainfall and flooded areas, such as parts of Bangladesh, straw drying is almost impossible during the rainy season. Where drying is very difficult, the feasibility of using urea or ammonia treatment as a preservative, as well as a means of improving digestibility and intake, should be studied.
Rice straw is regularly fed to ruminants throughout the rice-growing countries. It is often the main food of mature draught stock (cattle and buffaloes) over most of the year and they seem to work and survive on it despite its low digestibility and protein content. It is often fed ad libitum and sometimes grazed. This gives the animals the opportunity for some selection of the parts they consume. In those rice-growing countries where milk is traditionally consumed, rice straw is also fed to dairy cattle, and more especially buffaloes, but with supplements of green fodder and concentrates. Rice straw and husks have many uses other than animal feed and are traditionally used in brick-kilns, as packing material, and for paper-making.
White straws
The straws of the common temperate cereals have long been fed to livestock and are still very important in developing countries. Developments in harvesting methods may have affected straw quality in some parts of the world, and in the temperate zone especially. The traditional method was to mow the crop before it was in danger of shattering, then bind it into sheaves (originally cut by scythe or sickle and hand-bound; later mechanized by the reaper-binder), where the ripening and drying of the grain was completed before threshing, which might take place much later, with the crop stored in stacks in the interim. More modern methods, and especially the introduction of combine harvesters and grain drying, usually mean that the crop is cut at a slightly more mature stage than was the case previously, with more leaf loss and straw of lower feeding value. Modern clean-weeding by herbicides has greatly reduced the grasses and other edible herbage which, formerly, was mixed with the lower part of the straw.
Figure 37. Standard bales of barley straw grouped for field-drying and transport (Dunecht, Scotland)
Farmers' opinions differ greatly, from country to country, as to the feeding value of wheat straw. In western Europe it is considered very poor, and not fed except in emergency (oat and barley straw were the only ones recommended as feed in UK until modern straw-treatment techniques were introduced), but now it is used after ammonia treatment. In the traditional wheat-growing countries of Asia and North Africa, however, wheat straw is highly prized and great care is taken in collecting and storing it. The form of straw depends on the threshing method. Where threshing was by flail, long straw is produced, and modern threshers give the same result. Where threshing was through treading by animals or with a ridged roller, the straw is broken into pieces 5 - 10 cm long (tibn, bhusa) and this system was very widespread in North Africa and Asia. Treading has now often been replaced by threshers; those used in India and Pakistan are constructed to chaff the straw during threshing. Chaffed straw is often stored in tightly-packed stacks, mud-plastered to protect them from rain and livestock. Mud covering can also be used to seal stacks for urea treatment.
Oat straw is a good and palatable roughage, as is barley. These straws are easily collected, handled and baled in mechanized systems with ordinary haymaking equipment.
Figure 38. Straw of foxtail millet (Setaria italica) in carefully built and thatched stacks (Gansu, China)
Straw of small millets
The straw of foxtail millet (Setaria italica), which is an important crop in northwestern China, is well accepted by livestock. Finger millet (Eleusine coracana) straw is considered a good feed in India and Nepal; the heads ripen unevenly and are hand-harvested in stages; the straw is cut and dried thereafter. The straw of common millet (Panicum miliaceum) is hairy and its palatability mediocre.
The residues of maize, sorghum and millets are major forages in developing countries, and maize stover is also widely used in commercial agriculture. In small-scale farm systems, stover is usually handled and dried in the long, unchopped state, often by stooking in, or on the boundary of, the field prior to storage. In large-scale systems it may be baled, but can also be collected by forage-harvester and ensiled with or without urea treatment.
Maize Stover
Maize is the best of the cereal stovers for livestock feed. Where very abundant in relation to the livestock, it can be grazed off; otherwise, on large enterprises, it can be ensiled or collected and dried. Many small-scale farm systems collect the stover when the cobs have been harvested and either dry it in the field or at the homestead. In some places of fuel scarcity, even the roots are dug up together with the stem bases and used as fuel. Cut stover can be ensiled if chopped, moistened, well compacted and sealed.
Maize stover has a higher nutrient content than most straws, with about 6% CP. In North America, it is frequently fed to dry, pregnant cattle as basis of their ration; either grazed or chopped, and fed with or without being ensiled. It is often stored by stacking or baling after field drying.
Sweet-corn cobs, now a widely-grown commercial vegetable for fresh use, canning and freezing, are harvested while the plant is still green, and thus provide a large yield of high-quality roughage as a by-product. Sweet-corn stover benefits from being left growing a few days after harvest of the cobs. Maize is often harvested as roasting cobs, for sale in urban areas; as it is at a more mature stage than sweet-corn, the stover from such plants is a superior feed (or if dried, hay) compared to that from a fully-mature crop.
Figure 39. Roof-top storage of straw and stover - it also helps keep the animals warm (Gilgit, Pakistan)
Sorghum stover
This is a valued feed, especially if cut and dried immediately after the heads have been harvested for grain. Frequently, the heads are hand-harvested as they ripen and the stover harvested separately, preferably by cutting as green as possible after seed harvest and field drying in the same way as sorghum hay. Grazing in situ is done in some countries, but it is potentially dangerous because of the likelihood of cyanogenic substances in any re-growth, and also wasteful, as is always the case with grazing of stover. The stems of tall, robust varieties are used for fencing, building grain cribs and other light construction work.
Bulrush millet
A coarse, poor feed, usually reputed to be of low palatability; it is nevertheless popular in parts of India. Under small-scale farm conditions, the heads are hand-harvested and the stover cut once grain harvest is complete.
Residues of pulse crops
Many of these have a higher feeding value than cereal straws, but are much more difficult to recover; in humid climates the leaves tend to discolour or drop at or before harvest, and in dry conditions they shatter. Where the final drying of the crop takes place at the homestead, it is easier to recover the leaves and stems. The leaves and stems of other commonly grown pulses, but not described below, are many of them also useful feeds, such as the various Phaseolus spp., green and black grams, and the leafy parts of pigeonpea. Fava beans, however, have coarse, woody stems, while the straw of chick-pea (Cicer arietinum) has a very high oxalic acid content, is unpalatable, and reputed to be toxic.
Groundnut tops as "hay"
In areas where good drying weather occurs at harvest time, very useful hay can be produced from groundnut haulm. Groundnuts should be dug when the leaves begin to change colour to a yellowish shade and the haulms begin to dry. Sever the tap root and dig up the nuts then windrow and dry the foliage. The partly dried haulms may be stacked in small heaps. In the drier parts of Asia, groundnut tops are carefully harvested and then dried at the homestead, on house roofs and other sunny places protected from livestock. They may also be stacked on stakes, dried for 3 to 6 weeks and then threshed: the straw from this method is useful, despite its appearance.
Pea haulms
Green vines from canning, fresh and freezing crops are a valuable by-product and are best conserved as silage. The frozen pea crop is a large one, mainly grown in developed countries. Pease straw, from fully mature plants for dried pea production, is a useful roughage.
Soybean haulms
The haulms from hand harvested crops when properly cured are a useful feed. Successful harvesting is, however, very dependent on suitable weather and often the leaves are diseased or senescent by harvest time.
Cowpea haulms
These are an excellent fodder and are carefully stored in countries where the climate at harvest time is suited to drying. They are traditionally used in sheep-fattening in the Sahelian zone.
Storage systems have evolved with the many crops and livestock production systems associated with crop residues. Often they are similar to those used for hay and described in Chapter III. The methods of storing white straws depends on the threshing system (i.e., whether long straw or chaffed). Long straw is often stacked and thatched, or small quantities are stored on house-roofs, in lofts and outbuildings. Tree storage is also used, to keep it above the reach of livestock. Stacking should be on dry foundations of stone or brushwood. Chaffed straw is mainly produced in semi-arid areas; tightly packed stacks or heaps protected with mud plaster are a common system for storing large quantities. These may be in a corner of the field, on waste land or near the eventual point of use. In dry areas, such stacks are made directly on the soil.
Rice straw is always long (and almost impossible to chaff). The care taken in its storage and conservation varies greatly from place to place. Usually it is roughly heaped, either on field edges or where livestock are kept or gathered at night. Often, the stock are allowed direct access to the stack and eat selectively. It should preferably be fed in addition to other feed. Where there is an overall scarcity of roughage, however, rice straw is stored with more care and may be put in the crotches of trees, or in stacks protected from stock. Cattle shelters with the straw stacked on the flat roof are used in some areas.
Stovers are still grazed in some countries, especially in parts of Africa; this is wasteful but does save a lot on labour and returns some dung to the fields. Where dried roughage is highly valued and there is a dry season after harvest, stovers are usually dried in sheaves, and in dry areas are often stored by stacking the sheaves together with the stems more or less vertical.
Production of more and better conserved straw for livestock feed could be attained in several ways. Dual-purpose varieties of cereals - where straw quantity and quality are taken into account in addition to simple grain yield- are one approach, but their extension will depend very much on the economics of straw and livestock vis à vis grain, as well as the grain quality of such varieties when grown for subsistence. The general trend in cereal variety development has been towards shorter growing cultivars with less straw; the "stay green" quality of some maize cultivars, however, not only helps increase their grain yield but also provides a better stover for animal feed.
Improvements can be made to straw yield (or recovery) and quality, without changing cultivars, by attention to agronomic details at the time of harvest and immediately afterwards. Where the whole crop is cut at harvest, the straw should be dried as quickly and thoroughly as possible, and stored with care. Where heads or cobs are hand-gathered, the cutting and drying of the stover or straw should be done immediately grain harvest is completed, with the fields protected from grazing livestock in the period between grain harvest and straw collection. Stooking of maize and sorghum allows final ripening of the grain after the plant is cut; this provides stover of better feeding value than if the crop is allowed to mature standing. Topps and Oliver (1993) give some analyses from Zimbabwe (Table 7). As with hay, careful carting and storage (with or without baling) are very important.
Table 7. Effect of stooking maize on stover composition
|
Stage of cutting |
TDN (%) |
Protein (%) |
Digestible protein (%) |
|
Stooked |
45 |
4.0 |
1.0 |
|
Late-cut |
40 |
3.0 |
2.0 |
Field handling and baling
The mechanized handling of the straw of small cereals is similar to that of hay, as described in Chapter II. Since straw is from the mature and relatively dry plant, and much less leafy, it is much easier to cure than green herbage. Windrowing followed by pick-up baling can often be done soon after the combine-harvester has passed. Straw to be transported off the farm is often made into high-density bales - over 200 kg/m3.
In small-scale farm systems, the crop is usually taken to a central point for threshing (which may or may not be on the field). The straw will therefore have to be taken from the threshing area for final drying, if not already dry enough (especially likely in the case of rice). With some crops and harvesting systems, most of the straw may be left in the field after the heads are harvested; e.g., rice in some systems, and finger millet: such straw should be harvested and dried as quickly as circumstances allow. Small-scale farms usually store straw un-baled, long or chaffed according to the crop and threshing system.
Straw treatment improves both quality and conservation. When straw is treated with an alkali, the ester linkages between lignin and the cell-wall cellulose, polysaccharides and hemicelluloses are hydrolysed, thus causing the carbohydrates to become more available to the micro-organisms in the rumen. Sodium hydroxide was used but has problems of cost and handling. Anhydrous ammonia or a solution of ammonia in water is now used. Gaseous ammonia is best suited to large operations and can only be used where the distribution system for ammonia (tankers, cylinders) is available. It has the great advantage that the straw can be treated in the bale when baled material is being treated. Ammonia acts as a fungicide (the process also creates anaerobic conditions) while also increasing crude protein content. Treatment requires airtight conditions.
For small-scale farms, it is generally more convenient to generate ammonia from urea, a widely-available fertilizer which is familiar to most farmers, by the "wet ensiling process". Ammonia is produced from urea, which is broken down by the action of urease (NH2-CO-NH2 + H2O ® 2NH3 + CO2), through bacterial action, when it is mixed with moist straw; the process is rapid at high temperatures and so is suited to subtropical and tropical conditions rather than to temperate climates or subtropical winters.
The following description of straw treatment with urea is from the FAO (1993) publication Tropical Feeds:
"Of the chemical treatments available, urea treatment has the most relevance to small farmers. Urea is added to the straw at the rate of 5% w/w (air-dry basis). The quantity of water may range from 0.3-1 l/kg of air-dry straw, with a minimum being applied in areas with water scarcity. If the straw is wet with rain or with freshly harvested straw containing much green material, urea can be applied without prior dissolution.
"Straw can be kept in various ways during treatment. Airtight conditions produce the best results. The conventional method is to use plastic sheet. A concrete silo, above ground and lined with plastic, will invariably produce good results, but concrete and bricks can be costly and difficult to obtain in some circumstances. A construction of earth bricks (clay mixed with straw), as used for making houses or storing rain in parts of Africa, is also suitable. Oil-drums or plastic bags can be used for very small-scale (single animal) quantities. Alternatives can be worked out locally: in dry areas, they can be below-ground pits lined with straw, banana leaves, or bamboo leaves or mats; in wetter areas, they can be stacks against a wall or fine-mesh wire (chicken wire) containers. When straw is stacked against firm structures (walls, pits, meshed wire), trampling can be done to compact the material and wet straw will not allow air to enter. Even if 100% airtight conditions are not achieved, good results can still be obtained and the outer (untreated) parts can be fed to animals with lower requirements, such as draught bullocks or dry cows, while the inner part is fed to growing and lactating animals.
"Treatment time may vary from 1 - 4 weeks. In intensive work undertaken in Bangladesh and Sri-Lanka in the early 1980s, 7 - 10 days was normal, with no benefits in animal performance obtained by longer treatment. However, temperature and treatment time are inversely correlated and more time is required in winter or in colder climates. In well-compacted straw, the temperature rises over 10°C after one week."
Figure 40. Urea-treated straw being taken from a mud-cased heap. Note the berseem behind (Punjab, Pakistan)
A detailed description of small-scale farm processing of straw with urea is given by Dolberg in FAO's Better Farming Series (FAO, 1995c), and gives the differences between treated and untreated straw shown in Table 8.
Table 8. Expected effect of straw treatments
|
Untreated straw |
Treated Straw |
|
Poor-quality feed |
Reasonable-quality feed |
|
Unpalatable, so animals eat little |
Palatable, so animals eat more |
|
Animals lose weight |
Animals gain weight |
The signs of successful treatment are given as:
- The straw has changed colour to dark yellow or brown.
- The straw has a strong ammonia smell.
- The straw is softer than untreated straw.
- The animals, after a period of adapting, eat one-third more than untreated straw.
The equipment needed for simple, small-scale treatment is a means of weighing straw (usually several standard bundles or baskets would be weighed and volume measures used thereafter); a volume measure for the standard quantity of urea used; a ten-litre bucket and a large water reservoir; the concentration used is 5%, or ½ a kilogram in 5 litres of water for every 10 kg of straw treated. Whereas straws need not be chopped before treatment, stovers must be, unless they can be very well compacted.
Urea treatment should be timed to fit in with crop-harvesting operations and wherever possible done before the straw or stover has already been stored or stacked, to avoid double handling and extra labour. This will also help ensure that the straw is in good condition; dirty, mouldy or rotten straw must never be treated as the result would make a poor and potentially dangerous feed.
Straw in standard and big bales is suitable for ammonia treatment as the ammonia gas can diffuse through the straw without pre-mixing or opening of bales. Many farms now use anhydrous ammonia as fertilizer. Some of the ammonia reacts with the straw to provide some nitrogen available to the rumen microflora. Anhydrous ammonia or a 35% aqueous solution are used. The straw must be completely sealed - usually under plastic sheet. Standard bales are stacked 50 ´ 4 or 5 bales wide, in stacks of about 30 t on a plastic sheet; the top is slightly ridged to shed water; the whole is covered with another plastic sheet which is sealed by weighting. The sheet may be roped or netted as protection against wind. Ammonia is injected through holes in the sheet, which are immediately sealed with a special seal. Big bales can be stacked, but care is necessary; they are usually put in plastic sleeves, singly or in groups, and injected. The site for storing treated big bales must be carefully chosen to ensure drainage, and access at the time when they are to be used.
Sugar cane
The tops of sugar cane, the terminal leaves, the bundle sheath and one or more nodes are a valuable feed. The point of cutting depends on the millers' requirements, but is usually at the highest fully-formed node. Quantities vary with cultivar, management practice and growing conditions, but is of the order of 18% of the aerial biomass and a reasonable crop can, therefore, provide 5 t/ha of dry matter. Where cane cutting is seasonal, livestock often depend on cane tops during the winter harvesting season when other feed is scarce. For example, in the sugar growing areas of the Indo-Gangetic plain, canes are often a welcome source of roughage at the end of winter. The tops are readily accepted by livestock, but are low in protein and require supplementation. Where animals can graze them selectively or if the dry leaves are removed, their feeding value is improved. Cane tops can be conserved as silage. Sugar cane can be grown as a fodder and is unusual in grasses in that it has its highest energy content at maturity. It can be chaffed and fed direct, or ensiled; cane can also be fractionated using simple crushers, so that the juice is used for monogastrics and the residue for ruminant feed.
The wastes from processing - bagasse and molasses - are also useful feed sources, especially the latter, which is high in readily available energy, but these are agro-industrial by-products. Bagasse is also used as fuel and in the manufacture of particle-board. The residues of artisanal cane-crushers has much more sugar left in it than factory bagasse and is a much more useful feed in consequence.
Sunflower heads
The threshed heads of sunflower, provided that they have been dried before threshing (this depends on the climate), are a valuable feed. In the Trans-Nzoia area of Kenya, where sunflower is grown for bird-seed, the crop is harvested by cutting the stem at waist height with a sloping cut when the seeds are fully formed, cutting off the seed-head and spiking it, seed-side down, on the cut stem to dry and avoid bird damage. The heads are further sun dried before threshing. The threshed heads, which may contain some seed, are then put through a coarse hammer mill before being added to ruminant feeds. The crude protein content of the heads is 7 - 9%. Once dried, they can be stored for long periods. With the tall, grey-striped cultivar in a reasonable crop (2 t/ha), the ratio of seed-head to seed was around 1.2. The stems are poor feed and are usually either ploughed in or used as fuel. In Zimbabwe, heads are sometimes dried once the seed has formed and then ground, without threshing, as feed. Topps and Oliver (1993) give the crude protein content of the resulting meal as 14% and the crude fibre as 25%.
Cotton sticks
The leaves, twigs and unripe bolls of cotton are eagerly browsed by small ruminants after harvest and are a good feed, but only if the insecticide regime of the crop has been a suitable one! Sticks can be dried for winter feed, with the thicker stems used as fuel.
Miscellaneous moist residues
Not all crop residues suitable for livestock are dry. Many fresh residues are locally important as feed sources. Sugar beet tops are a good feed, but are conserved by ensiling, not drying (the pulp - a very valuable feed - is an agro-industrial by-product). Horticultural crops produce large quantities of herbage which, while not consumed by humans, is nevertheless useful animal feed and used opportunistically. The unsaleable parts of brassicas (and a hectare of cauliflower can yield a lot) are usually only suitable for feeding fresh. Sweet potato tops are an excellent feed, equivalent to good legumes. Yam peelings are traditionally fed to backyard sheep and goats in the yam belt of West Africa. Banana pseudo-stems are useful roughage, widely used as cattle feed - they are not suitable for drying, but can be ensiled. Some tree prunings are useful feed, especially for small ruminants, but they are usually available only sporadically and browsed on the spot, and often the bark is eaten as well as the leaves (e.g., mulberry poles in the Himalayan region).
Where tree prunings are available on a large scale, the leaves may be conserved for local use. The olive, which is cultivated on large areas in the Mediterranean zone of Europe and North Africa, and now also grown commercially in the Americas, provides large quantities of twigs and leaves at pruning. These are highly palatable to livestock. It is preferable to feed the leaves green, but they may be dried for later use or stripped off the branches and ensiled. Undergrade fruit and some wastes from fruit and vegetable processing (citrus marc, pineapple waste, pea haulms) are conserved as silage.
