which is less demanding than sow and piglet production. The
amount of manure transported to the fields is inadequate to meet
crop demand, partly because only some of the total amount of
manure produced was applied to fields. This was due to the
transport distances involved, the farmers have difficulties in
transporting the manure to the fields; therefore, farmers instead
have to use relative high amounts of inorganic fertilizer. This is
especially the case in the Hue province where transport distances
are long.
The surveyed data also indicate that there is a relation between
the presence of a biogas plant and the amount of land available for
the construction of the digester. One must bear in mind that the
farm buildings are situated in villages and not within the fields, and
thus on some farms there may not be room for a biogas digester
near animal houses. Still, only six of the non-biogas farmers gave
too little land for the plant as the rationale for not installing
digesters (Fig. 1).
3.2. Animal production
Diets fed to the pigs were a commercial high protein and
carbohydrate feed, a local feed or a mixture of a local and
a commercial feed. The local feed consisted of agricultural residues
such as rice bran mixed with cassava leaves, water spinach, banana
tree, water hyacinth, sweet potatoes or soybean. The local ingredients
are traditionally cooked before feeding. The mixed feed
consisted of different rations of local and commercial feeds. Biogas
is an obvious energy source for preparing the local feed, but this
was not reflected in a higher proportion of mixed feed used on
biogas farms.
For all pig categories, mixed diets are the most commonly ration
used on both biogas and non-biogas farms (Table 4).
Commercial diets are fed to sows on biogas and non-biogas
plants on an average 10% of all farms. Piglet productions on farms
in Hue are fed a mixed diet. In the Hanoi region, 28 and 34%,
respectively, of non-biogas and biogas farms use commercial feeds
for fattening pigs, whereas these numbers are, respectively, 0 and
8% in the Hue province. Pigs fed commercial diets grow faster than
pigs fed mixed and local feeds due to the higher level of easily
digestible protein and carbohydrate. However, mixed diets are
preferred by most farmers because these diets are cheaper and the
growth rate can still be acceptable. In most developing countries
mixed diets are common, for example in African countries like