Fallows, set-aside and their Agronomic, Economic and Environmental
Functions ; a Diagnosis
1. Fallowing: the traditional functions and research results
2. The problems linked to the reintroduction of fallowing
(set aside) in France
3. The importance of fixed or long-term fallows
To conclude
Fallowing used to be one of the main cropping practices in Europe and is
still practised in many countries. Owing to the evolution of the Common
Agricultural Policy (CAP), fallowing is once again being considered as a
means of reducing cultivated land. In order to limit the production of cereals,
oilseeds crops, and protein crops (COPs) and in the framework of the new
CAP, all farmers who wish to benefit from "direct aids" must set aside 15%
of their cumulated cultivated land, when exceeding a certain production
threshold.
Even if this method does not always efficiently limit production (Jacquet,
1993), it has many consequences and should thus be studied, specifically
in arable farming regions. In France alone, over one million hectares are
concerned, a considerable area representing roughly 10% of all "cultivable
land". Under the present EU regulations (Official Journal of the European
Communities, 1/07/1992, 6/08/1992), and if we overlook the so-called
"industrial" fallow (1), we can define
the concept as an area that produces no crop over a certain period of time,
i.e. from 15 December 1992 to 15 July 1993.
Historically, fallowing was justified by the functions it fulfilled from
an agronomic standpoint, and at the level of production units or traditional
terroirs. Results on the effects of fallowing have been obtained in
Europe (at Rothamstead and Grignon, for example), in the USA and in Third
World countries. These experiments were carried out in different climatic
and land conditions and in various socio-economic contexts, and the resulting
knowledge has enabled us to develop a theory on the "traditional" fallow
(Sebillotte, 1985). In the first part of this paper, we will recall the most
important aspects of this theory, which is still a perfectly valid argument
to justify the agronomic effects that would result from reintroducing the
fallowing system.
However, our knowledge of the "traditional" fallow can only be transferred
if we are aware of the radical difference between the earlier and the present
context: the "traditional" fallow developed as a coherent adaptation both
to former techniques and the functioning of farms; the situation is totally
different nowadays as the factors driving agricultural change (i.e. the technical
evolutions) have on the contrary led to rejecting this crop practice. We
are therefore talking about reintroducing this practice in a context where
it no longer spontaneously has its place. Thus, in the second part, we will
examine current problems arising from reintroducing fallowing on farms, in
particular problems linked to a constraining regulatory framework.
The rigidity of the present framework and the limited scope adopted in the
texts that define the fallow - known as set-aside - as a way to limit production,
both lead us to reflect on the importance of long-term or fixed fallows as
regards other objectives. Our reflection agrees with similar considerations
that are developing in several places.
[R] 1. Fallowing: the traditional functions and research results (2)
We will first examine the functions of fallowing that were explicitly sought
after, i.e. the "previous effects", effects on the environment following
the fallow period, or other functions linked to the production system.
We will then briefly take a look at the other important effects of fallowing
on the environment, as these must be considered if one is to produce a
comprehensive diagnosis of the practice.
In this context, there are two types of fallow:
- the bare and cultivated fallow,
- the grass-covered and grazed fallow, frequent in livestock farming areas.
I will not deal with forest fallow.
1.1. The bare and cultivated fallow
1.1.1. Functions
This practice consists in keeping the soil free of plants (bare) - as far
as possible - for at least one year.
Agronomic functions:
In the oceanic regions of Northern France and Europe, fields were mainly
fallowed to control weeds (3), a "direct"
control based on repeated mechanical destruction. Tilling induced the germination
of weeds, thus reducing the seed stock in the soil. The results were extremely
variable according to the tools used and the way they were used. Later, chemical
weeding (sometimes associated with surface cultivation) had similar but less
intense effects as the seed stock to was destroyed in a thinner soil
layer (4).
In drier climates, farmers are still trying to reduce the seed production
of weeds ; however the main objective is that of water storage. Fallowing
was therefore encoded in the "rules" of dry farming. However, experimenters
disagree about the value of this technique; Sebillotte (1985) explains these
contradictory results by the determining effect of the respective positions
of wet periods and fallow periods on the final water balance, amongst other
things.
Other functions:
Historically, in many regions, fallowing was also practised to enable ploughing
operations to extend over a long period of time; this would have been impossible
in the lapse of time between say two autumn crops. Repeated surface cultivation
tillage was used to control weeds over a long period of time and most probably
progressively refined the structural states of the soil, thus helping to
achieve a satisfactory "seed bed" in the autumn, even though the tools used
were not highly efficient. This was especially important in areas with dry
summers and autumns.
The organisation of work throughout the year was particularly important in
agricultures based on animal traction. Indeed, since animals could not change
their work speed, one solution was to increase their numbers (two animals
per team) with the result that the fodder crop area also had to be increased.
To maintain the best balance between areas dedicated to draught animals and
directly productive areas, the rule was to spread work out over the year
(Heuzé, 1862).
It must be added that the mechanised agricultures of North Africa still resort
to the same arguments to limit their equipment and labour costs.
1.1.2. Other previous effects
Bare fallow favours the mineralisation of organic nitrogen. However, the
climate is the main factor that determines the quantity of mineral nitrogen
stored in the soil within reach of roots at the end of the fallow period.
The results obtained by Yankovitch (1956) in Tunisia have been widely confirmed:
depending on the water balance of the rain period during fallowing, the fallow
will accumulate nitrogen to be used by the plants or will be a source of
pollution due to leaching of nitrogen (and possible runoff). This contributes
to explaining the contradictory effects of fallows on the yield of future
crops in systems that do not used mineral fertilisers.
Fallowing also has an effect on soil parasites: it the host plants are destroyed,
then the inoculum contained in the soil will be reduced. However, in relatively
extensive traditional conditions (with perhaps less pressure from diseases),
this effect has little effect on future crops and is therefore not much sought
after.
If the soil is too damp when cultivators are used to destroy the weeds, the
structural state of the soil may be deteriorated due to packing effects.
1.2. The grass and grazed fallow
1.2.1. Main function
This type of fallow is generally introduced following a cereal crop. Its
objective is to feed a herd by letting it graze the stubble and weed and
cereal regrowths. In the East of France, this practice, along with that of
free grazing of local herds on the harvested village fields, justified the
triennial partition of space corresponding to the fallow-wheat-secondary
cereal rotation.
1.2.2. Previous effects
Effects on the weed seed stock
The probability of maintaining the weed seed stock in the soil is high, but
depends on the way the herd is managed, as this conditions the emergence
and maturation of the plant reproductive organs. The same problem arises
when a forage crop is sown to replace a fallow
(5).
Effects on water storage
The effects on the hydric balance vary according to the climate, the importance
of regrowth and grazing periods. In regions such as North Africa, where fallowing
is an essential and practically unique source of food for animals, tilling
is carried out late in the season so as to increase this resource, generally
after the rain period. Therefore, the possibility of storing water is extremely
limited in these dry climates (Besse and Sebillotte, 1992).
Effects on the dynamic and storage of nitrogen
The dynamic and storage of nitrogen are influenced not only by the climate
and tillage date, but also by the animal species, the stocking rate and the
weed type (legume or non-legume). In general, the presence of plants tends
to reduce the risks of nitrogen leaching. We must add that the presence of
animals leads to a transfer of mineral elements and organic matter between
the fields, linked to the choice of stabling or penning areas (excretion
areas) and according to the future use of these fields.
Effects on the soil structural states:
Fallowing can lead to the creation of favourable structural states, particularly
in the case of sufficiently dense grass swards; however, trampling by animals
often result in soil packing. However, as these swards do not remain on the
plots for a long period of time, they do not improve the soil structural
stability (Monnier, 1965), in spite of the moderate inputs of organic
matter.(6)
Therefore traditional fallowing was often the only way to face up to difficult
situations whether relating to agronomic or to other problems (feeding the
herd, work organisation). It was an adjustment practice, and is still
considered to be so in the countries where it is practised.
Besides, whether in the case of bare or grazed fallows, agronomists know
that changes in soil states depend on the way the fallow is cultivated and
on climatic events. They consider that there are several types of fallow:
to understand the variation in the real effects of fallowing and the
contradictions observed in the literature, one needs to simultaneously take
into account the unfolding of a climatic and a cultural history.
[R] 2. The problems linked to the reintroduction of fallowing (set aside) in France
Farmers may benefit from support measures until 1996. A majority of farmers
may therefore reasonably be expected to adopt set-aside for general economic
reasons (Jacquet, 1993). Given the regulatory requirements, farmers are faced
with several questions: which fields should we set aside? How will we technically
manage these fields during the fallow period? Should we sow a plant cover?
These questions should be dealt with at two levels:
- that of fields, to examine the current validity of previously acquired
knowledge.
- that of farms, to examine all the repercussions of this practice - as defined
in the new CAP - on the farm functioning and viability.
2.1. The agronomic problems at the field level
We will deal only with the case of rotational set-aside , as it is the only
type of fallow allowed under the CAP. Rotational set-aside works on a yearly
basis and may bear a plant cover (sown or not) or remain "bare" (at least
in 1993).
There are two main differences with the "traditional" fallow:
- on the one hand, it is now introduced in an intensive farming system, based
on strict control of crop pests (Meynard and Girardin, 1992).
- on the other hand, this type of fallow is subject to strict environmental
requirements, just like all other crops.
This leads us to examine the question of set-aside management, in particular
as regards these two problems.
2.1.1. Set-aside management
Fighting crop pests
These "new" fallows should be managed in such a way as to curtail the
multiplication of weed reproductive organs and thus the increase of soil
seed stocks, and the dissemination of crop enemies to neighbouring fields,
as fallow plants (weeds and crop regrowths) are potential hosts for parasites
and insects with relatively well-known effects. It is essential to control
the evolution of weed seed stocks, not only as regards the yield objectives
of the following crops, but also as regards the quality requirements for
crop cleanliness - for one because it economises on cleaning the grain. It
is also indispensable to protect fields against intrusion of outside
pollen…
Knowledge acquired on the "traditional" fallow shows that successful control
is difficult to achieve, as confirmed by all the farmers who have introduced
this practice over the past two years (Bizot and Le Quiniou, 1992).
In the case of bare fallows, one method is to keep the soil free of
weeds (at least free from the species most dangerous for the following crops)
and crop regrowths, during the whole set-aside period with the help of herbicides
and/or repeated passages of cultivators. However, the list of authorised
active matters is limited, and in both cases, there is a major risk of being
unable to sufficiently control the production of reproductive organs: indeed,
just a few weeds are enough to maintain the seed stock in the soil (Debaeke,
1987). At all events, these practices will be a source of expenses.
Depending on the way it is managed, set-aside can have a positive or a negative
role in fighting weeds. Treating the fallow like a pseudo-seedplot could
be extremely useful to control crop regrowths, with surface tilling to encourage
seed germination, then destruction before maturing and seed shedding. This
could, for example, avoid excessive use of herbicides to control rape regrowths
in sugar beet crops.
In grass covered fallows, the sward will strongly compete against
weeds and finally "choke" them (Fisher and Davies, 1991; Hébrard et
al., 1992). But here again, there is still the risk of maintaining the
seed stocks in the soil.
Moreover, the success of sowing a plant cover is not at all guaranteed: it
depends on the demands of the selected species, on the climate at the time
of sowing and therefore on the harvest date of the previous crop. Experience
shows that in trying to reduce sowing costs, farmers often achieve fairly
rough seedbeds, with detrimental effects on germination and growth regularity
and thus on the sward evenness.
Finally, the destruction of the plant cover and what becomes of its residues
remain problematic.
Environmental conservation
As regards the control of nitrate and pesticide pollution, the assets
of grass-covered fallows are obvious, as the plant cover reduces risks of
nitrate leaching and pollution of surface waters due to erosion (nitrates
and pesticides). The new CAP authorises (at least in 1992-93) bare fallow
methods, which is rather surprising given it declared concern for environmental
protection; however, this seems to be due to late publication of the texts.
Given the knowledge acquired on the "traditional" fallow, research should
now turn to the effects of the bare fallow system on the soil organic matter
(content and composition) compared to fallows with grass. The nitrogen
mineralisation dynamics may be disrupted, especially if "minimum" soil tilling
is practised during the bare fallow stage, as suggested by some
agronomists.
Indeed, although simplified tilling limits mineralisation, and sometimes
reduces leaching (Goss, 1990), would not deep-tilling be necessary each time
the fallow is introduced following a crop that has deteriorated the structural
state of the soil? What effect would this have on the environment? What pollution
risks would such alternating soil cultivation practices entail? Moreover,
minimum tilling also raises the question of what becomes of crop residues
and their role in soil inocula evolution.
Studies on pollution risks due to pesticides are also needed, in particular
in the case of bare fallows with herbicide applications.
Last, as regards control of soil erosion, I will simply recall that
a sward, planted for a year or more, can contribute to slightly improving
the soil structural state and to reducing risks of run off erosion; on the
contrary, bare fallow maintained by cultivation of the soil increases risks
of packing and erosion.
This demonstrates that fallow management must imperatively be considered
in relation to the cropping system, as we will see hereafter.
2.1.2. The place of fallows in the crop systems
The agronomic point of view on fallows results from a comprehensive approach
to the crop system. The studies to be undertaken must also adopt this approach.
Fallows play an essential role in crop systems: for instance, a fallow may
perhaps not be best placed after a cereal crop. As affirmed by some agronomists,
one needs to examine the previous effects, the crop response to soil states
and the technical means at the disposal of farms in the light of the economic
context.
On a wider scale, the presence of fallows may call into question the
"conventional" intensification of other crops. For instance, from both an
agronomic and an economic standpoint, it may be preferable not to suppress
all the weeds in each crop. Weed control still implies the total eradication
of all undesirable plants, including during the fallow stage, but should
preferably be considered as a dynamic balance to be maintained throughout
the crop succession, given the above-mentioned risks. On the contrary advantage
could be taken of the fallow to significantly reduce the seed stocks in the
soil, so as to adopt less intensive weed control methods in the future.
Studies should also be carried out on the long-term management of weed covers
and crop regrowths in fields, in relation to the place of fallows in the
crop succession. In the framework of these studies new tools to vigorously
"cut back" the vegetation without destroying it - based on the principle
of the "landaises" used in tropical plantations - could be designed and tested
for spontaneous plant covers, that are less more economical than planted
covers.
It would also be interesting to use the grid developed by Sebillotte and
Meynard (1990) to analyse risks of nitrate pollution. The grid combines the
effects of crop systems with environmental characteristics. For instance,
in the case of or well planned fertiliser applications on the deep soils
of the Parisian Basin fields, what are the risks of nitrogen pollution after
harvesting crops with low residual nitrogen (sugar beet, maize) in the
autumn?
Finally the studies to be carried out should answer two objectives:
- that of increasing the flexibility of fallow management, which should be
modifiable at all times since fallows are subjected to economic
constraints;
- that of limiting the failure risks of agricultural techniques applied to
fallows, risks linked to the fact that their effects depend not only on the
place of fallows in the crop succession, but also on the climate, whether
regarding effects on parasites, weeds or "leaking" nitrates.
2.2. The role of fallows in farm functioning
For most farmers who will adopt the set-aside system and not be in a position
to set up "industrial" fallows, economising on operational or structural
costs will continue to be a necessity.
2.2.1. Operational costs and work schedules
Reduction of operational costs will need to be addressed in the framework
of the agronomic options discussed earlier in this paper
(7) Extensive-type approaches could offer valuable
perspectives if appropriate technical management itineraries could be designed
for the other crops (Meynard and Limaux, 1990). These new technical itineraries
would, however, require even greater technical savoir-faire on the farmers'
part.
Work schedules will need adjusting to the management modalities of crop systems
including a fallow stage. We may reasonably expect a lessening of work peaks
in the autumn (these are the reason for the high-capacity machinery observed
in arable farming areas), and at a lesser level, in the spring, as the work
tasks will be spread out over other periods. The probable variability of
technical choices made by the farmers will probably induce a diversity of
nuances.
2.2.2. Structural costs
Work needs will be probably be lessened if 15% of all COPs are replaced by
fallows. Setting land aside will reinforce the farmers' objectives of cutting
down their structural costs. However, as support measures may not be continued
after 1996, the courses that farmers will take to reduce their salaried
labour force and equipment costs (the only cases examined in this article)
will chiefly depend on their individual situations.
Each time gains can still be made under these headings, farmers will seize
the opportunity to reduce salaried labour; i.e. on the occasion of
the transfer of the farm to a successor, the creation of an association or
with the departure of an employee. The introduction of set-aside is not expected
to slow down the move of farmers living in the major French arable regions
towards forms of work in common. This will probably even accelerate it owing
to changes in their agricultural machinery.
Farm equipment
Indeed, faced with uncertainty about the measures that will be adopted after
1996 and given the lifespan of their machinery, farmers will probably do
their best to make the present equipment last as long as possible; the question
of what to choose will arise chiefly in the case of imperative machinery
replacement.
The price of machinery and their present size on the farms lead to several
options.
Certain expensive machines (such as combine harvesters) with oversized capacities
may risk becoming unprofitable. In the case where these need replacing, set-aside
can either contribute to changes in the modes of machinery appropriation
(shift to collective ownership (8), resort
to mutual aid) with equipment that is more efficient, or lead to purchasing
less performing machinery if the farmer remains the sole owner. Large but
less expensive machinery, such as sprayers, will probably be replaced
identically.
For machinery with more accurately calculated work capacities, such as tilling
or sowing equipment, replacement will probably be dictated by the difference
between the area that can be worked with the present machinery and the threshold
area beyond which machinery size will need to be increased.
- If the workable area is close to the threshold-area, the introduction of
set-aside will probably result in more comfort at work peak times, by better
performing the work or keeping to the times scheduled for interventions on
the remaining fields. This will entail a degree of intensification, and may
lead to replacement with identical machinery.
- If the workable area is significantly lower than the threshold-area, the
introduction of set-aside areas will make currently-sized machinery non
profitable, and will therefore lead to a similar evolution as that described
for combine harvesters.
Besides, new machinery may be needed to work the fallows, which also raises
the issue of their profitability (9).
Will farmers use this argument to resort to outside help? Will they be tempted
to question their technical choices and "take the plunge" for all their other
crops, for example regarding simplified tilling or mechanical weed control?
It must be added that if the increasingly frequent reintroduction of mechanical
hoeing in beetroot crops and suppression of weeding are both indicative of
the need to invent more economical methods, return to these "traditional"
techniques has been made possible by the continuous improvement of hoeing
equipment.
Finally, the problem of flexibility mentioned above will also play a role
in the choice of machinery. Thus although rotational fallows are still the
rule, farmers will choose to apply less basal fertilisation to the rotation
head crop, as they cannot always decide in advance about the place of the
fallow in the rotation; they will therefore need to keep significant spreading
capacities so as to adapt.
The reinstatement of fallows as "CAP fallows" will have many consequences
on the functioning of farms and on their structural costs; but contrary to
"traditional" fallows and given the uncertainty about the Community measures
that will apply after 1996, will these consequences be globally positive
on the long-term?
[R] 3. The importance of fixed or long-term fallows
In the current regulatory texts, fallows are necessarily rotational. This
point of view is much debated. It is indeed to be regretted that the modalities
of fallow management are defined on the basis of one objective only, that
of limiting production. If set-aside was applied to one field for several
years or permanently allocated to one particular site or field, or if it
could be returned more or less often to the same field, this could:
- on the one hand, contribute to improving work productivity, a major demand
of farmers.
- and on the other hand, contribute to better conservation of the environment,
as set-aside could become a means of land management; this leads us to consider
a regional-level approach
3.1. Improving work productivity
The first way to improve work productivity is to take advantage of the positive
effects of the sowing swards (grasses, alfalfa) lasting more than two years.
The advantages would be: weed control (mainly annual species), improvement
of soil structural states and organic matter content (Sebillotte, 1980),
etc. This would induce greater input efficiency and lessen crop susceptibility
to climatic variation. In certain conditions, farmers can also use this method
to "restore" fields when planning to change their crop system.
The second way is to improve the field shape to facilitate fieldwork. The
field margins and headlands could be permanently sown with grass and treated
like a lawn. Of course, it weeds would need to be controlled, but don't road
verges pose the same problems?
Finally, it seems regrettable to exclude, a priori, grazing from fallows:
in some cases viable extensive livestock systems could be achieved by having
several farms group their fallows together.
3.2. Improving conservation of the environment
The fixed fallow offers a means of fighting runoff erosion in some regions
(Papy and Boiffin, 1989): this can be done by growing a grass cover on the
cultivated parts of the erosion-susceptible watershed thalwegs. Of course,
the upkeep of these areas will pose some problems, the main difficulty being
the selection of an appropriate plant cover. It must be added that this method
has been successfully experimented, for instance in the pineapple plantations
of the Ivory Coast.
Control of nitrate pollution can benefit from sowing perennial swards on
riversides, or in low-lying hydromorphic areas (they have been shown to lay
a considerable role in denitrification, Merot and Curmi, pers. com.); these
practices are well developed in Germany, for example. However, since permanent
grassland areas are not taken into account in the calculation of EU support,
they are often ploughed up, with a resulting twofold increase in nitrate
pollution (from mineralisation of organic matter and reduction of denitrification
- although this last point can also be positive in terms of "global
change").
A third way is to permanently eliminate lower quality plots and those that
entail risks for the environment. We will of course need to think about the
sward to be planted, the effects on the landscape and on the dynamics of
crop enemies. But is that a good enough reason for rejecting a method that
can also have a positive influence on other features (game, for example)?
"Traditional" fallowing was above all a means of technically adapting to
the constraints of the ecological environment in given socio-economic contexts.
The aim of the new CAP is allegedly to contribute to solving economic problems
by reintroducing this agricultural practice, but with particularly rigid
specifications: a fixed return length and interval on the same field, obligatory
rotations, and prohibition of many herbicides, of grazing… As a
counterpoint, the main feature of our analysis is the great diversity of
functions that fallows could fulfil and the great variety of concrete management
modalities that could be adapted according to the farm or ecological environment.
It is obviously impossible to make precise economic predictions on the value
of introducing set-aside. There have apparently been major misunderstandings
and the reactions of farmers who plough up their permanent grasslands underscore
some of the deep incoherences between the different regulations of the new
CAP.
Immediate economic calculations will encourage the adoption of set-aside
until 1996. Even though there may be some doubts as to whether these measures
will be maintained beyond this date, fallows will not disappear entirely.
Research must therefore work on the flexibility aspects of this agricultural
practice. The modelling of crop systems is certainly one means to be considered
in priority, but it is not far advanced and lacks data on the dynamic of
spontaneous weed and crop regrowths, or on effects on the environment.
Like all new agricultural practices, we will only be able to judge the value
of set-aside after several years. Learning how to handle it adequately will
take time (10) This reinforces the need
for valid agronomic reasoning on how to manage crop systems as a whole. Intensive
and extensive crop management will probably coexist on farms.
However, the reflection that has been initiated, which takes into account
field observations should provide the means for exerting some leverage on
the evolution of regulations. The questions to be debated concern the
introduction of fixed fallows where this is justifiable, the modification
of the return interval on the same field, etc. The objective is for this
agricultural practice to be considered from an agronomic, economic and
environmental point of view, so as to introduce it judiciously, as one of
the relevant means of adapting agriculture to the many requirements that
it must now meet.
This article is taken from the "Courrier de l'environnement
de l'INRA, n°20", by M. Sébillotte, S. Allain, T. Doré
and J.-M. Meynard.
Translated from French by Nicole Scott.
[R]
(1) We will not refer to "industrial fallows"
that correspond to crops grown under a contract guaranteeing their industrial
use. At first glance, there is no difference with other crops. However, these
crops (rape, beetroot...) are liable to become too numerous in the crop
successions and may induce phytosanitary problems. Moreover, their presence
is likely to have a consequence on the farm functioning and especially on
equipment decisions: acquiring high-performance machinery to deal with
intensified work peaks, or replacing machinery still considered useful, rather
than resorting to outside help. Finally, we should recall that under the
current regulations the grazing of animals on fallow land is prohibited during
the fallow periods and even beyond that period (but this point is still under
discussion).[VU]
(2) Many references can be found in Sebillotte (1966, 1985),
but have not been mentioned here.[VU]
(3) Sigaut (1975). Fallowing was introduced in the "Broadbalk"
tests (Rothamstead, 1924) to control weeds at the rate of one year out of
five.[VU]
(4) That of cultivating the soil, which brings seeds to the
surface.[VU]
(5) This is the case in the Australian "annual legumes
(Medicago)-wheat" system. Introduced in North Africa, on livestock farms
with herd management methods that could not guarantee the control of plant
covers to avoid the proliferation of weeds and their germination; this resulted
in a high degree of weed infestation.[VU]
(6) We will not deal with long-or short-term temporary
grasslands, grown in the place of fallows to feed a herd and achieve a range
of agronomic effects. These are mentioned in Sebillotte
(1980).[VU]
(7) We should add that supplying companies (or their
agents who may do so on their own authority) push farmers to increase their
inputs consummation, by arguing that the quotas to be attributed would be
higher in the case of high reference
yields.[VU]
(8) CUMA (Coopérative d'Utilisation de Matériel
Agricole") or joint-ownership.[VU]
(9) Farmers who have livestock consider themselves to be
privileged as they are already equipped with machinery to harvest the forage
crops and can use this machinery on the grazed
fallows.[VU]
(10) One sign is the difficulty in having measures to
curtail nitrate pollution adopted (Schellenberger and Soulard,
1993).[VU]
[R]
Besse T., Sebillotte M., 1991. Ann. INRAT, Tunis, n°
spéc., 64, 240, (167-188).
Bizot E., Le Quiniou V., 1992. Doc. mult., FDGEDA de Seine et Marne, 14 p.
Debaecke Ph., 1987. Thèse Doct. Ing. INA PG, Paris, 342 pp.+ annexes.
Fischer N.M., Davies D.H.K., 1991. Br. Crop Protection Conf. Weeds,
387-394.
Goss M.J., 1990. In R. Calvet : Coll. "Nitrates, agriculture, eau", COMETT,
INRA Editions, Paris, 576 pp., (389-394).
Hébrard J.P., Barthélémy P., Bodet J.M., Orlando D.,
Massé J., Mathieu J., Viaux Ph., 1992. Persp. Agric., 173,
39-70.
Heuze G., 1862. Les assolements et les systèmes de culture. Hachette,
Paris, 534 pp.
Jacquet F., 1993. Démeter 93, Economie et stratégies
agricoles. A. Colin, Paris, 243 pp., (15-73).
JOCE, 1992. Réglement Conseil n° 1765/92.
JOCE, 1992. Réglement Commission n° 2293/92.
Meynard J.M., Girardin P., 1991. Cour. Cell. Envir. INRA, 15, 1-19.
Meynard J.M., Limaux F., 1992. Aménagement et Nature, 105,
16-19.
Monnier G., 1965. Thèse Doct. Ing., Univers. de Paris. INRA, Paris,
140 pp.
Papy F., Boiffin J., 1989. Soil Technology Series 1, Catena-Verlag,
D-3302 Cremlingen-Destedt, 29-38.
Sebillotte M., 1966. Rev. Agric. de France, 52, 169-184.
Sebillotte M., 1985. A travers champs. Agronomes et géographes.
ORSTOM, Paris, 297, 175-229.
Sebillotte., 1980. Fourrages, Paris, 83, 79-124.
Sebillotte M., Meynard J.M., 1990. In R. Calvet : Coll. "Nitrates,
agriculture, eau",COMETT, INRA Editions, Paris, 576 pp. (289-312).
Sigaut F., 1975. Et. Rur., 57, 89-105.
Yankovitch L., 1956. Ann. du SBAT, Tunis, 29,
1-223.
[R]
