ABSTRACT
The urban agriculture holds an important place to insure the
urban food security. On the Malagasy highlands, the lands traditionally
conducive to the culture of the rice or the market gardening are saturated. The
soil on the hills called locally «tanety» are widely
available for the agriculture. However, the main soil on these lands, the
ferralsol present biophysics and chemical constraints. The main objective of
this work was to study the culture of this kind of soil; in this context, the
major hypothesis is that the organic matter as amendment or fertilizer is
necessary. The specific objectives were to identify the traditionally practices
of organic fertilization in urban and peri-urban agriculture, to estimate the
perception or the quality of organic matters that farmers used and their
agronomic value in these cropping systems by analytical technics, and finally,
to determine the effect of the quality of organic matters to the ecosystem
services of soil.
The methodological approach was based on survey in the suburbs
of Antananarivo, laboratory and fields experiments. 149 farmers were randomly
enquired into 9 sites in urban and peri-urban zone to assess the soil fertility
management. Organic products used in the different cropping systems or
potentially recoverable in agriculture were analyzed to determine their soil
fertility value. Then, 10 farmers were enquired according to the base of their
cropping systems for the studies of fertilization driving. For the laboratory
experiments, mixtures of soil and organic matter was incubated with three types
of organic matters with increasing dose during 60 days in 28°C in the
darkness. The organic products tested in the laboratory were the
«terreau d'Andralanitra», natural compost from wastes
landfill, a compost made from sawdust and waste of slaughterhouses and the
manure used conventionally by the farmers. The various tested doses are 0; 5;
10; 15 and 29 g carbon.kg-1 soil. The same organic products were
tested in fields where two factors were tested, chemical fertilizer input or
not and the organic inputs. for the former, the «terreau»
and the compost inputs at 3 levels of supply on soil were compared to the
manure input and a control without input.
In the urban and peri-urban agriculture, the organic resources
and its quality showed a large variability. The farmers attribute generally a
value of an organic product by its granulometry form. The solid materials have
an improvement value of soil properties, while ashes or powder were considered
to have a fertilizers value. Substitution of conventional manure by terreau of
landfill or burnt waste was observed in some case. The carbon mineralization of
the organic product manure was more important than the C mineralization
observed with the «terreau» or with the compost. According
to the supply levels of organic inputs the rates of mineralization in after 60
days of incubation decreased from 28 % to 18 % of organic carbon (CO) of manure
and from 24% to 7% of CO of terreau and compost. Only the compost
released significant mineral nitrogen amount. The manure inputs showed a
slightly net N mineralization in spite of a high mineralization of the organic
carbon. The N immobilization by microbial biomass might be hugh. After three
years of the maize crops on a ferralsol with the different tested organic
inputs, the crops grain and biomass yields were higher on organic inputs
comparatively to the control without inputs.. The association of an organic
supply and a chemical fertilizer accentuated this effect. Without NPK, the
accumulated yield over 3 years of culture varies according to the quantities of
organic products brought from 3 to 7.7 t.ha-1 with contribution of
compost, the yield are on average, of 2 in 2.7 t.ha-1 with
«terreau», while they affect 3.5 t.ha-1 with manure for a
conventional dose, and 1,1 t.ha-1 for the control. With NPK, the
accumulated yields obtained over 3 years vary 7-11 t.ha-1 with
compost inputs and, 4.6-7.6 t.ha-1 with terreau inputs while the
yields with manure and NPK was 6.5 t.ha-1, and 3,8 t.ha-1
for the control. After 3 years crops, the soil of the organic and mineral
supply treatment showed a slightly increase of the total nitrogen, but no
effect was highlighted on the total carbon of soil. The available
phosphorus in soil increased after three years with mineral and organic supply
but for the highest doses of organic inputs.
Key words : Organic matter, ferralsols, urban waste,
amendante value, fertilizer value, Antananarivo
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