Crop by-products: the best of the rest
For more than ten years the Department of Agriculture at the University of Reading in the UK, and ILRI in collaboration with KARI in Kenya, have been working on the principle of 'excess feeding' of crop by-products to livestock. By offering animals more than they can eat it has been shown that the nutritional value of stover increases. Dr Emyr Owen, a ruminant nutritionist working on crop-residues, explains that this is because of the selective feeding behaviour of ruminants (particularly small ruminants e.g. sheep and goats). "By offering the animals an excess of straw the sheep and goats are able to pick out the parts they prefer, namely the leaf and leaf sheath, which is the most nutritious part of the crop by-product."
Different livestock species have also shown distinct preferences in
the length of straw that is offered to them as feed: sheep and goats
prefer their straw chopped whereas research from Ethiopia on cattle
demonstrated that they preferred sorghum stover left as long stalks.
Cattle lack the prehensile upper lip of smaller ruminants and so are
unable to pick out the leaves as easily as sheep and goats.
The
ability of livestock to select against less nutritious or palatable
parts of a crop plant means that even the residues of bird-resistant,
and therefore in parts bitter, varieties (e.g. pigmented sorghums) can
be offered. The animals simply select those parts of the plant residue
that they find acceptable.
Further research in Kenya has shown that the stem, as the woodiest part of the plant, is most likely to be rejected. This is best treated with urea and then composted prior to being incorporated back into the fields. In fragile environments, such as in Niger, West Africa it could be argued that the crop stover should be ploughed back into the land immediately after harvest and not removed to be used as feed. The advantage with feeding the crop residues to livestock is that the rejected composted material, and the manure from the animals, can still be returned to the land to increase the organic and nitrogen levels of the soil.
'Feed your animal - feed your soil' is also a concept adopted by Indonesians, particularly in Java where agriculture is very intensive. Cattle are kept in pens and fed on fodder cut from the roadside. The 'cut and carry' method of feeding is labour intensive but the rich manure that is produced is essential to maintain soil fertility in farmers' fields. Livestock are given large quantities of fodder for selective feeding and the 'waste' then falls through the wooden slats of the livestock pens to be composted with the manure from the cattle. The manure/compost can then be taken out, treated and stored before being applied onto the fields at an appropriate time. Additional treatments to the manure-compost may include fire ash, kitchen waste and, in Nepal, farmers add leaves from particular tree species to enrich their compost further (See Agroforestry and local knowledge - New Agriculturist 98-3). In fact the leaves may be given direct to livestock to chew, trample and urinate on in order to 'process' the leaves to release essential nutrients necessary for improving soil fertility. After the necessary treatments, the compost-manure is then stored, ('cooked') under banana leaves for a period of time to allow aerobic and anaerobic bacteria to partially decompose the material and to make nutrients more readily available for applying to the fields.
Where agriculture is not as intensive, farmers may choose to stall-feed livestock for a short time of the year only. For instance, in Gambia, women bring the cattle into pens for a few weeks and feed them on groundnut hay, millet stover and bran produced from the kitchen. The manure is then collected, managed and applied to their kitchen gardens to improve horticultural yields. The high value produce obtained is then sold at Banjul or Dhaka markets to provide valuable income. As Jon Tanner of ILRI points out, "Livestock are important to turn the nutrient 'crank' that powers the 'engine' of soil fertility."
