Titre : L'Agronomie tropicale
Auteur : Centre de coopération internationale en recherche agronomique pour le développement (France). Département des cultures annuelles. Auteur du texte
Auteur : Institut de recherches agronomiques tropicales et des cultures vivrières (France). Auteur du texte
Éditeur : Institut de recherches agronomiques tropicales et des cultures vivières (Paris)
Date d'édition : 1975-10-01
Notice du catalogue : http://catalogue.bnf.fr/ark:/12148/cb34398560g
Type : texte texte
Type : publication en série imprimée publication en série imprimée
Langue : français
Description : 01 octobre 1975 01 octobre 1975
Description : 1975/10/01 (VOL30,N4)-1975/12/31. 1975/10/01 (VOL30,N4)-1975/12/31.
Description : Collection numérique : Numba, la bibliothèque... Collection numérique : Numba, la bibliothèque numérique du Cirad
Droits : conditions spécifiques d'utilisation (sous convention BnF-ADM-2025-035729-01)
Identifiant : ark:/12148/bpt6k11003577
Source : CIRAD, BH_PEHIST 5290
Conservation numérique : Bibliothèque nationale de France
Date de mise en ligne : 02/05/2021
Summaries
VELLY (J.). — Silica fertilizing of rice in Madagascar.
Poor yields and the bad sanitary aspect of some rice fields in
Madagascar led to study silica fertilizing. Experiments were con-
ducted on peaty and mineral hydromorphic soils, on the East-Coast,
and organic hydromorphic gley soils and colluvium on the High
Plateaux.
Silica was applied as silicate of lime or paddy hulls burnt
or not burnt.
Silica applications markedly increase yields, on the soils of the
coastal area, where deficiencies are the highest. There is a high
increase in the silica contents of rice (straw, leaves and grains)
and a decrease in nitrogen and phosphorus contents and manganese
and iron contents. Rice health is significantly improved.
The silica contained in the hulls is very rapidly used and silicate
of lime has a longer effect on the peaty hydromorphic soils. Silica
applied as hull ash is poorly efficient when applications are made
at very high temperatures (vitrification).
The content of silica in rice straw at harvest permits to have an
accurate diagnosis of deficiency. A beneficial effect of silica ap-
plications can be expected when contents are lower than 10 %.
On the peaty hydromorphic soils of the East Coast, even with an
application of 9 t/ha of silica, it was not possible to observe a
significant fall in the response curve. Yet, in case of deficiency,
an application of 3 t/ha of silica can be considered as absolutely
necessary. The amounts of silica removed by rice, principally by
annual double crops, are very high and so seem to be the drainage
losses.
Where this is possible, the systematic turning under of rice straw
and hulls would already be an important progress as regards
maintenance application.
NICOU (R.). — The problem of caking with the drying out of
sandy and clay sandy soils in the dry tropical zone.
Most sandy and clay sandy soils in the dry tropical zone form
into a mass as soon as they are dried, which makes deep tillage
difficult.
Ploughing is one of the main means to improve the soil fertility
but its introduction in the. agricultural calendar of the farm involves
a number of problems which could be solved only by reducing the
cohesion of the dried soil.
It is shown that caking depends on several factors: texture, mois-
ture, drying rate, porosity, properties of the clay cement. Never-
theless insufficient is known about the origin of the phenomenon
and further investigations are needed to determine its mechanism.
It seems that the problem concerns mainly the properties of the
clay humus complex.
Meanwhile caking can be partially modified by some management
practices. It is recommanded to plough in organic matter at least
every two years, alternatively with ploughing without turning under
whenever possible. Then dry ploughing in the less clayed soils
could be attempted. To prevent too high a degradation of the
structure created any intervention such as trampling for hand
weeding, grazing of the breaks in rotation should be avoided.
DIATTA (S.). — Evolution of the plateau soils under crops in
continental Casamance. Results of two - year experiments.
The plateau soils of Continental Casamance are an important part
of the areas to be cultivated in Senegal. They present two types
of problem.
— the problem of regenerating the completely degraded lands
which have been under crops for a long time.
— the problem of developing the recently cleared soils.
Long-term experiments were established to study the evolution of
these soils under different cropping systems in relation to the
yield of the species cultivated.
The two first years already give some information:
1) The problems related to the regeneration of the degraded soils
seem easier to solve than those of the newly open lands. While
giving satisfactory increases in yields, tillage and fertilizing alone
cannot bring a complete regeneration which first results from
organic matter.
2) Development involves problems particularly marked for the
traditional crops (groundnut, millet) and to some extent rainfed
rice. Maize adapts, itself more rapidly to the ecological changes
due to clearing. The problem seems complex and needs further
studies.
EGOUMENIDES (C.), PICHOT (J.). — Effect of the method of
application of phosphorus on the evolution of the element in a
soil with a high fixation capacity.
In many tropical soils phosphorus deficiency limits yields but
sometimes, despite the good contents of total and available phos-
phorus, it is the high fixation capacity of the soils for phosphorus
which is the limiting factor.
Experiments were carried out in pots on a humic hydromorphic
gley soil from Tananarive area which has such a fixation capacity
and to which phosphorus was applied in a liquid and solid form.
They seem to show that the correct phosphorus supply of the
plant can be obtained with located fertilizers or fertilizers of low
solubility.
VELLY (J.). — Silica fertilizing of rice in Madagascar.
Poor yields and the bad sanitary aspect of some rice fields in
Madagascar led to study silica fertilizing. Experiments were con-
ducted on peaty and mineral hydromorphic soils, on the East-Coast,
and organic hydromorphic gley soils and colluvium on the High
Plateaux.
Silica was applied as silicate of lime or paddy hulls burnt
or not burnt.
Silica applications markedly increase yields, on the soils of the
coastal area, where deficiencies are the highest. There is a high
increase in the silica contents of rice (straw, leaves and grains)
and a decrease in nitrogen and phosphorus contents and manganese
and iron contents. Rice health is significantly improved.
The silica contained in the hulls is very rapidly used and silicate
of lime has a longer effect on the peaty hydromorphic soils. Silica
applied as hull ash is poorly efficient when applications are made
at very high temperatures (vitrification).
The content of silica in rice straw at harvest permits to have an
accurate diagnosis of deficiency. A beneficial effect of silica ap-
plications can be expected when contents are lower than 10 %.
On the peaty hydromorphic soils of the East Coast, even with an
application of 9 t/ha of silica, it was not possible to observe a
significant fall in the response curve. Yet, in case of deficiency,
an application of 3 t/ha of silica can be considered as absolutely
necessary. The amounts of silica removed by rice, principally by
annual double crops, are very high and so seem to be the drainage
losses.
Where this is possible, the systematic turning under of rice straw
and hulls would already be an important progress as regards
maintenance application.
NICOU (R.). — The problem of caking with the drying out of
sandy and clay sandy soils in the dry tropical zone.
Most sandy and clay sandy soils in the dry tropical zone form
into a mass as soon as they are dried, which makes deep tillage
difficult.
Ploughing is one of the main means to improve the soil fertility
but its introduction in the. agricultural calendar of the farm involves
a number of problems which could be solved only by reducing the
cohesion of the dried soil.
It is shown that caking depends on several factors: texture, mois-
ture, drying rate, porosity, properties of the clay cement. Never-
theless insufficient is known about the origin of the phenomenon
and further investigations are needed to determine its mechanism.
It seems that the problem concerns mainly the properties of the
clay humus complex.
Meanwhile caking can be partially modified by some management
practices. It is recommanded to plough in organic matter at least
every two years, alternatively with ploughing without turning under
whenever possible. Then dry ploughing in the less clayed soils
could be attempted. To prevent too high a degradation of the
structure created any intervention such as trampling for hand
weeding, grazing of the breaks in rotation should be avoided.
DIATTA (S.). — Evolution of the plateau soils under crops in
continental Casamance. Results of two - year experiments.
The plateau soils of Continental Casamance are an important part
of the areas to be cultivated in Senegal. They present two types
of problem.
— the problem of regenerating the completely degraded lands
which have been under crops for a long time.
— the problem of developing the recently cleared soils.
Long-term experiments were established to study the evolution of
these soils under different cropping systems in relation to the
yield of the species cultivated.
The two first years already give some information:
1) The problems related to the regeneration of the degraded soils
seem easier to solve than those of the newly open lands. While
giving satisfactory increases in yields, tillage and fertilizing alone
cannot bring a complete regeneration which first results from
organic matter.
2) Development involves problems particularly marked for the
traditional crops (groundnut, millet) and to some extent rainfed
rice. Maize adapts, itself more rapidly to the ecological changes
due to clearing. The problem seems complex and needs further
studies.
EGOUMENIDES (C.), PICHOT (J.). — Effect of the method of
application of phosphorus on the evolution of the element in a
soil with a high fixation capacity.
In many tropical soils phosphorus deficiency limits yields but
sometimes, despite the good contents of total and available phos-
phorus, it is the high fixation capacity of the soils for phosphorus
which is the limiting factor.
Experiments were carried out in pots on a humic hydromorphic
gley soil from Tananarive area which has such a fixation capacity
and to which phosphorus was applied in a liquid and solid form.
They seem to show that the correct phosphorus supply of the
plant can be obtained with located fertilizers or fertilizers of low
solubility.
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