Organic Soil Fertility Management of Lowland Rice Farmers in Bilar
and Dagohoy, Bohol, Philippines: A Case Study
CBDC Bohol Project, SEARICE, Philippines
Year 2001
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The project provided technical assistance to farmers converting
to organic soil fertility management. This is a part of the
project’s overall goal of promoting sustainable agriculture. The
conversion to organic farming was gradual to avoid possible
drastic loss in yields. Farmers started with small plots using
chicken manure as the organic material. Other farmers used compost
materials such as dried rice straw and dried leaves of Gliricidia
sepium and Mekania cordata. Some farmers are evaluating mixed
organic-inorganic farming. The staff documented the farmers’
evaluation on the use of organic fertilizers and its effect on
soil properties and crop performance. Farmers evaluated the
results of their experiments for one or two seasons and then
expanded the area using organic fertilizers.
The use of organic fertilizers has addressed the soil fertility
and the cost-production problems of farmers. They have observed
that the use of organic fertilizer is comparable with commercial
fertilizers in terms of production or yield of rice After three
seasons into organic soil fertility management, approximately 20
hectares of ricefields in Bilar and Dagohoy have been converted to
organic farming. Other farmers in the area have already started
converting to organic farming after observing the results of the
trials done by the organic practitioners. The project expects the
total area of organic farms to increase further as more farmers
will be using chicken manure as organic fertilizers in the coming
season.
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The CBDC – Bohol project has evolved different strategies and
methodologies in enhancing farmers’ awareness on sustainable
agriculture (SA) including ecological pest management (EPM) and
soil fertility management (SFM). It is the project’s goal to
transform the current conventional agriculture of its
partner-communities into sustainable farming. The project provides
technical assistance to farmer-partners undertaking conversion to
organic farming.
A season-long farmer’s field school (FFS) training was conducted
in three villages of Bilar and Dagohoy, where 55 farmers
participated in the weekly-field school. The FFS training promoted
sustainable farming practices among farmers, which trained them
and enhanced their awareness on ecological pest management, soil
fertility management and participatory plant breeding. The
training promoted the use of organic fertilizers which also served
as an approach to encourage farmers to go "organic." In
addition, the training aimed to encouraged farmers to reduce if
not eliminate the use of pesticides and instead rely on the
cultural control of pests.
This study is a documentation of farmers’ adoption and
experimentation on organic farming of lowland rice, especially in
Bilar and Dagohoy. The documentation includes farmers’ methods
and approaches in restoring natural soil fertility and farmers’
adoption of organic farming as measured by their indicators of
improvements in their farming systems. The case study also
documented farmers’ problems and barriers in the adoption of
sustainable farming.
The study’s results will serve as an additional contribution to
the already existing approaches and methodologies in sustainable
farming. This would be able to support, concretize and
substantiate the concepts of organic farming. The farmers’
experiments on organic fertilization would further validate the
viability of organic agriculture as a good alternative to
conventional farming. In addition, farmers’ observations and
evaluations of their on-farm experiments will further validate
scientific findings and studies conducted by agricultural
researchers and scientists. These farmers’ researches and
experiments will also emphasize their roles as researchers and
innovators in agriculture.
This case study is also intended to show how organic
farming is interpreted and practiced by farmers in Bohol and serve as a
guide to farmers who want to go into organic farming.
On-farm trials
The project assisted the farmers in designing and implementing
their on-farm experiments on organic soil fertility management.
Farmers observed their plants, their soil and their farm
ecosystem. Field observations were also done by the project staff
to monitor and document farmers’ evaluations and observations on
the results of organic materials on soil properties and plant
performance. Individual interviews were also conducted for each
farmer to document the lessons and problems they encountered in
the adoption of organic farming.
A farmer’s field day was conducted by the participating farmers
to evaluate and assess the various field trials. Other non-organic
practicing farmers also visited and observed the on-farm trials so
they would be able to see how things were being done in the
experiments. Community workshops and group discussions were then
held and synthesized the evaluation results from the project
staff, the individual farmer and the group.
Farmer-respondents
Farmer-graduates of the FFS training were selected for the case
study. The study identified farmers who had been practicing
organic farming for more than three seasons and had converted a
big area of their field into organic farms. However, the
respondents were not limited only to the identified
qualifications. Farmers with less than three seasons of organic
farming as well as farmers who are into mixed organic-inorganic
farming were included in the research.
The project interviewed 15 farmer-respondents in three villages
namely, Campagao, Cansumbol and Malitbog. The qualified
farmer-respondents have been using organic materials such as
chicken manure, dried rice straw and crop residues as organic
fertilizers. Some of the farmer-respondents have been practicing
zero farm-inputs or natural farming.
Reasons for shifting to organic farming
Conventional farming is completely dependent on chemical inputs,
which cause harm on the agricultural system: on plants, animals,
insects, soil, and on the producers and consumers of farm
products. Many farmers feel that a shift from conventional farming
to organic farming would reduce some of the adverse effects of
agricultural chemicals, and in the long term would ensure a more
stable, sustainable and profitable agricultural system.
Farmers were aware that organic farming is laborious and produces
low crop yield. Yet, almost all of them preferred organic farming
and took initiatives to experiment on it. This is because they
considered it as sustainable and they were aware of its benefits
in addressing their soil degradation, economic and ecological
problems.
Most of the practitioners considered economic reason as the major
determining factor in adopting organic farming. Farmers converted
to the technology because they observed that organic farming
requires lower production cost. They realized that the crops had
become too dependent on chemical fertilizers and pesticides and
they were getting into debt and could no longer afford to buy the
required inputs.
Motivations for shifting to organic farming practice
|
Reasons for shifting |
Number of times cited* |
|
Less production inputs |
13
|
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Restores soil fertility |
12
|
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Good crop performance |
2
|
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Retains soil nutrients/fertility |
4
|
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Prevents soil acidity |
5
|
|
Sustainable |
2
|
|
Restores waterlogged soil |
1
|
|
Trial / experiment |
3
|
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Challenged |
1
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*Out of 15 farmer-respondents
Aside from economic problems, some farmers were worried about the
depletion of soil fertility in their farms. They observed that
their soils have become dry and hard, acidic, difficult to prepare
for planting, with low water-holding capacity and barely capable
of sustaining plant life without fertilization. One farmer
commented that the natural fertility of the soil is already
destroyed because of the continuous application of chemical
fertilizers,
Some farmers also cited ecological and environmental reasons in
explaining their shift to organic method. In most farming systems
today, natural mechanisms of regulating the population of pests
and other organisms have been replaced by artificial methods such
as pesticides. Farmers felt that this was effective and essential
for rice production. They adopted spraying so quickly because
credit and pesticides were available, then.
However, farmers are now aware that using chemical pesticides
often leads to health problems, pollution and to the disturbance
of ecological balance.
Approaches and methods in organic farming
Almost all of the organic practitioners in the study had practiced
ecological methods of farming before the Green Revolution period.
They had used traditional methods such as recycling of crop wastes
and animal manure, composting, and cultural control of pests.
Hence, the concept and methods of organic farming were no longer
new to the FFS participants. Farmers formulated their individual
plans on how to undertake the conversion to organic farming and
designed their own trials in testing the new technology. They
identified the size of the area for their trials, the kind of
organic materials to use and as well as the rice varieties to
plant. Farmers implemented and managed their own field conversion
trials.
The conversion process varied among farmers. Some farmers started
with parcels of land being apportioned to organic farming while
other parcels relied on chemical inputs. According to them, this
gradual conversion was done to avoid drastic yield losses. They
started with small plots using organic fertilizers, such as
chicken manure and dried rice straw. They then evaluated the
results of their experiments for one or two seasons and then
expanded the field area using organic fertilizers.
Another approach was the mixed organic-inorganic farming. Rice
straw and chicken manure are incorporated during plowing and the
commercial fertilizer (ammonium phosphate or urea fertilizer) is
applied one month after transplanting. Farmers are slowly reducing
the use of chemical inputs (fertilizers and pesticides) in their
fields. According to them, since they are still in the transition
stage of conversion, changes have to be made gradually.
Eventually, they will resort to pure organic farming.
No farmer totally converted his whole rice field abruptly into
organic farming. According to the farmers, this is the most
crucial and risky method of conversion. To them, a lot of changes
and experimentation would be done first in order to reach a stable
system of farming. The farming system should be flexible in
following the approach that best enables it to cope with changes
during the conversion process.
Farmers have also developed alternative insect pest control. Out
of the 15 farmer-respondents, only four were using chemical
pesticides, but only on a case-to-case basis. They use chemical
pesticides as a desperate last resort only during intense
pest-attack to avoid yield production loss. Farmers control pest
attack through cultural methods. Repellent plants are planted on
rice dikes; a clean environment and a balanced ecosystem are
maintained or rat traps are built to control rats; and golden
snails are hand picked or trapped in bamboo slats in irrigation
canals. Farmers still believe that natural/cultural methods of
controlling pests are always better.
Varieties used
The farmers used different rice varieties for their organic
trials. These included varieties distributed by the project such
as breeding lines, segregating materials, traditional varieties (TRVs),
farmers’ selections (FS) and modern varieties (MVs). Farmers
sought to find out the kind of fertilizer (pure organic, pure
chemical or mixed organic and inorganic) most suited to their
varieties. They also wanted to determine the response of TRVs and
HYVs to these kinds of fertilizers. For them, it is very important
to obtain varieties that will perform well without pesticides and
chemical fertilizers. The key here is for the farmer to experiment
and develop his own seed variety.
The project also provided wider options of varieties to farmers to
enhance their skills and experience in evaluating and selecting
varieties and to enhance the rice diversity in the community. If
farmers have diverse rice varieties, their fields can adapt more
to changes and be more stable. For example, some varieties not
preferred by the pest can survive pest outbreaks.
The farmers considered the general characteristics of the variety
in choosing what variety to plant, i.e. yield capacity, good crop
performance, market value and eating quality. However, they
differed in varietal preferences.
Soil fertility management
Lowland rice areas are the most intensively cultivated, and in
order to produce higher yield from these areas, farmers have used
chemical fertilizers. However, crop yields and soil fertility has
declined because of the excessive use of chemical fertilizers.
According to Murakami (1991), continuous application of chemical
fertilizer, especially NH4+ based turns the
soil acidic which results to the non-availability of some
essential nutrients. The decline in soil fertility and soil
productivity is associated with the lowering of the soil organic
matter content. It is therefore necessary that the soil organic
matter must be maintained at adequately high level for a more
satisfactory crop yield (Murakami 1991).
Majority of the farmer-respondents have observed and complained
about soil problems such as low fertility, acidity (tested through
a soil test kit), waterlogging and poor soil structure. They
observed that the main reason for the soil degradation and acidity
is over-dependency on chemical fertilizers applied to the soil.
They then developed various techniques to improve or maintain soil
fertility. They have used organic matter such as recycled crop
wastes (dried rice straw, decomposed crop plants) and animal
wastes such as chicken, carabao and pig manure. They have also
used organic compost waste material.
Use of rice straw and organic compost waste material
Farmers spread rice straw evenly in the field right after
threshing. The straw is allowed to decompose and then incorporated
during plowing. Incorporating rice straw is a simple way of
increasing nitrogen (N) content of soil (SIBAT 1993). According to
Vacharotayan and Takai (cited by Dhanyadee 1993), the application
of dried rice straw increases rice yield. Capati (cited by Cosico
in 1985), also stated that this practice has been shown by
long-term experiments to generally produce higher rice yields than
burning or removal from the field. Analysis of the rice straw
composition used by farmers in Bohol showed that it contains 0.91%
N. Rice straw incorporation can indeed substitute for chemical
soil fertilization for the N requirement.
Results of analysis of the different organic materials used by
farmers in organic fertilization
|
Organic material |
MACRO/MICROELEMENTS (%) |
|
N |
P |
K |
Ca |
Mg |
Fe |
Zn |
Cu |
Mn |
|
Gliricidia sepium |
3.44 |
0.24 |
2.86 |
1.01 |
0.22 |
0.03 |
0.006 |
0.001 |
0.003 |
|
Mekania cordata |
3.24 |
0.35 |
2.71 |
0.89 |
0.44 |
0.11 |
0.010 |
0.002 |
0.010 |
|
Dried rice straw |
0.91 |
0.03 |
1.28 |
0.28 |
0.15 |
0.14 |
0.002 |
0.001 |
0.030 |
|
Chicken manure |
5.63 |
1.07 |
2.94 |
0.37 |
0.5 |
0.24 |
0.060 |
0.010 |
0.050 |
|
Organic compost |
0.28 |
1.35 |
0.30 |
0.69 |
0.36 |
3.50 |
0.120 |
0.005 |
0.060 |
Farmers also experimented on the use of composted waste material.
This was collected from a garbage site in a nearby province and
decomposed for almost three years. Farmers incorporated the
organic compost in the soil and plowed this together with other
organic materials such as chicken manure.
Use of crop waste materials and leguminous crops
Farmers also fertilized their soil organically through green
manuring with some leguminous crops. Two farmers used mungbean (Vigna radiata).
They planted mungbean after harvesting rice and then plowed this
under the soil during land preparation when the mungbean were at
the peak of their vegetative growth.
Farmers used other plants such as Mekania cordata and
Gliricidia sepium as green manure. They air-dried the leaves of
these plants, allowed these to decompose and then incorporated
these in the soil during plowing.
According to studies (Cosico 1985), using young leaves of these
leguminous plants provide nitrogen and other nutrients to the
soil. Leguminous crops fix nitrogen from the atmosphere in
symbiotic balance with rhizobium. The plant tissues of these crops
contain significant amounts of nutrients which are made available
to succeeding crops when crop residues are returned and left to
the soil to decompose. Green manure is most suitable for improving
soil and can fix N at a high rate.
Use of animal manure
Another method used by farmers to improve their soil condition is
to use chicken, pig and carabao manure as organic fertilizer.
These are applied during land preparation. Direct application of
the dried animal manure was the most common method among the
farmers (Appendix Table 5). Some farmers also broadcast
chicken manure fertilizer after weeding, which is one month after
transplanting.
Animal manures are the second most abundant source of organic
fertilizer in the farm next to crop residues since farmers not
only grow rice but also raise farm animals. Manure has high
fertilizer value and is more readily decomposable (Cosico 1985).
It provides essential nutrients, especially P and K, and the N
requirement of crop.
Farmers’ observations and evaluations on the use of organic
materials
Organic materials have not been extensively used in the
Philippines, but evidences from researches and studies show much
benefit from its use. Plants respond positively to organic
materials. The foremost benefit is a longer-term productivity of
the land. These also improve and conserve soil fertility.
According to studies, organic materials contribute to the build-up
of organic matter in the soil when their residues are incorporated
unto the soil. The soil becomes more manageable and fertile. It is
only organic matter, which can provide the necessary elements
(nutrients) for growing plants and improving the chemical,
physical and biological qualities of the soil (Murakami 1991).
On crop yield
Based on different organic on-farm experiments by farmers, organic
fertilization produced comparable yields with inorganic
fertilization. In some farmers’ trials, a combination of organic
and inorganic fertilizers produced a better effect on crops than
when either was used alone. Still in some cases, the organic
materials were found inferior to inorganic fertilizers in terms of
crop yield, especially on the first season under organic
fertilization. According to farmers, however, with increasing cost
of chemical fertilizers, organic fertilizers could still be an
economical alternative.
Comparisons and observations made by farmers on
organic and inorganic methods of farming*
|
INORGANIC FARMING |
ORGANIC FARMING |
|
Expensive inputs |
less production inputs |
|
not laborious (easy to apply) |
Laborious |
|
soil becomes dry and hard |
soil becomes soft and black |
|
Continuous application of commercial fertilizer makes the soil
acidic |
restores waterlogged areas/ water-holding capacity |
|
plants become used to commercial fertilizers |
restores/retains soil fertility |
|
Fertilizer gives immediate effect to the plants with greener
color of leaves (but not throughout the growing stage of the
plant) |
gradual/slow growth of plants (leaves are yellowish during
early stage but will recover its greener color effect throughout
the growth stage of the crop) |
|
will lead to poor crop performance with continuous application
of commercial fertilizers |
crop performance is comparable with plants grown under
inorganic fertilization |
|
plants appear sickly (less number of tillers) if overdosed with
commercial fertilizers |
high tillering ability of plants/ panicles appear shiny and
without black spots |
|
needs more commercial fertilizer to produce high yield |
produces less yield during 1st season of organic
fertilization (but stabilizes after 3-4 seasons ) |
|
yield decreases with continuous use of commercial fertilizers |
produces almost the same yield with inorganic fertilization |
|
plants are easily attacked/infested by pests and diseases |
less or equal number of insect pests present/ same kind of
insects/pests present with those of the commercial farming |
|
no problem on the availability of source and supply of
fertilizers |
source and supply of local organic material is a problem |
|
not sustainable |
presence of weeds after harvesting |
|
not safe for consumption |
environmentally-safe |
* as cited by 15 farmer-respondents
On crop growth performance
Rice grown under organic fertilization differs from the growth
performance of rice applied with chemical fertilizers. Farmers
observed that there is a gradual release of nitrogen (N) in
organic fertilizer as seen in the leaves of the plant, which are
yellowish at vegetative stage. In contrast, rice plants with
inorganic N application have dark green leaves and appear healthy
at the early growth stage of the crop.
According to Ponnamperuma (cited in SIBAT, 1993), organic
fertilizers unlike chemical fertilizers) release nutrients at a
slower phase, which is in time with the peak demand of the crop.
In the case of rice, N absorption is greatest during the
vegetative and flowering stages. Organic N of rice straw is
released 2-3 weeks after incorporation into the soil. It was
during this vegetative stage of rice when farmers observed that
the leaves turned greener which lasted until harvest time.
On crop varieties
Farmers observed that the different varieties (TRVs, MVs, FS and
breeding/segregating materials) have comparable crop performance
under organic fertilizer. Some of the farmer-respondents reported
good performance of HYVs under organic inputs compared to those
grown under commercial fertilization. One farmer observed that any
variety, which are over-dependent on chemical fertilizers
performed better under organic fertilization. Another respondent
observed that low-input variety had better crop performance under
organic fertilization. Farmers concluded that generally, any
variety would have a better growth effect when grown under organic
fertilization.
On soil properties
All the farmer-respondents in the study looked at all aspects of
the soil, including texture and structure and not just nutrient
fertility. Their perception of a good soil is rather black, soft,
and rich in organisms, such as earthworms. According to Murakami
(1991), in technical terms, a good soil is well structured, with
optimal moisture, rich in nutrients and high in biological
activity such as microorganisms. Soft soil, which is good enough
for plant roots to be able to penetrate, is due to the high
organic matter content of the soil, which was built-up through
nutrient cycling and with incorporation, and utilization of
organic materials.
After using animal manure and crop wastes as organic fertilizer
for three consecutive seasons (see Appendix Table 5 for rate of CD
application), farmers observed that their soil became soft and
black. Previously, their soil was hard, dry, acidic and reddish.
They observed that soil nutrient adsorption remained longer in the
soil after using organic fertilizer. This was observed when the
soil was not fertilized with any organic or inorganic materials
for one season but still produced a good harvest. Farmers
associated this with the longer-time fertility and productivity of
the soil, resulting from organic fertilizers.
After three seasons of using chicken manure, one farmer-respondent
observed that the soil in his field, which previously was sandy
with low water-holding capacity, has improved. Crops showed better
growth performance and produced good yield. Perlas (1994) stated
that a good soil has a good water holding capacity (WHC). Water
may enter the soil but it is not stored. However, if the soil has
a good WHC, then greater amounts of water will be available for
the use of plants. The soil must have the right looseness or
porosity. A porous soil allows water and air to enter, which is
needed for the proper development of plant roots.
However, farmers also observed that different kinds of weeds grew
abundantly in their fields, especially right after harvest, when
they converted to organic farming According to the farmers, this
is an indicator that soil fertility has been restored. Some even
observed that these weeds were not present in their rice fields
before. Unfortunately, the kinds of weeds were not identified.
Weeds are good indicators of soil fertility (Murakami 1991) and
each weed has its own characteristics. Some grow in fertile soil
while some grow in poor soil. Weeds are good compost as well as
mulch materials. By recycling the weeds, soil becomes fertile.
On pests
Almost all of the farmer-respondents encountered pest problems
during the dry and wet seasons. Nine out of 15 respondents
encountered pest problems only when they were into commercial
farming and encountered fewer pests under organic fertilization.
The other farmers had observed an equal number and the same kinds
of pests under both organic and commercial farming.
Farmers also observed that while pesticides protect crops from
destructive insects, these also kill friendly insects and natural
predators of these pests. In addition, they observed that
continual application of pesticides even causes resurgence of
pests. They also observed that chemical fertilizers make the crop
more attractive to pests and diseases.
Organic agriculturists have long maintained that pests and
diseases are indicative of soil fertility problems. There are
already existing experiential evidences to support the convention
that organic fertilizers are less conducive to pests than are
conventional fertilizers.
Problems encountered by farmers in sustainable organic farming
Farmers have taken initiatives towards the practice of sustainable
organic farming but the reality of the farming situation is giving
them problems in their practice. Field-level implementation or the
adoption of the organic practice has been slow for a number of
reasons. These included lack of know-how and encouragement on the
alternative farming practice, lack of raw materials (organic
materials) for the required inputs, laboriousness of the
technology, organic marketing problems, non-ownership of the land
and most especially, farmers’ wait and see-attitude.
Most farmer-respondents in the study are farmer-tenants. They own
some land but the areas are too small. Their land properties have
been mostly converted to organic farming. However, the tenanted
lands are only applied with organic fertilizer if the landowner
also believed in organic farming. Nevertheless, some
farmer-tenants were able to convert the land they tilled, provided
the landowner got his equal share in the produce, whether
production was high or low.
Farmers find the alternative practice laborious, and they have to
source out the required inputs such as the locally-grown organic
materials and the chicken manure. The source of chicken manure was
not easy for them since it had to be imported outside their place.
Farmers already converting to organic farming expressed concern
over the long-term supply of chicken dung. According to them,
chicken manure brought about the same outcome as chemical
fertilizers. They were confident that this was the
"right" organic fertilizer and lost their initiative to
try other local organic materials. They were even very concerned
on the quality of the chicken manure used. They once experienced
using inferior manure that was not properly dried with many
trash/impurities inside the chicken manure sack.
Marketing of organic produced was also an issue raised by organic
producers. Farmers were concerned about the pricing, certification
and consumer awareness of organic products. Would farmers still go
"organic" even if their products are not certified as
organic and sold in the market with the same price as the
commercially produce rice produced?
Organic farming represents an approach to sustainable farming
which creates integrated, humane, environmentally friendly, and
economically sustainable system.
The biological, economical and environmental benefits that can be
derived from practicing organic agriculture point out that organic
agriculture is a viable alternative to conventional farming.
The farmers in Bohol have different adoption levels for organic
farming. Their success indicates that this alternative farming
system is viable for many other farmers. However, some farmers are
reluctant to try it out because of their negative presumptions
about it. Hence, they a need proper orientation, knowledge and
skills build-up. But farmers should not be forced to adopt the
whole integrated system. Rather, they should be introduced to the
system gradually, to be familiarized and oriented with its methods
and allowed to think and try-out their own methods.
Farms have their inherent biophysical characteristics which need
to be considered. The present fertility level of the soil should
be considered in designing the proper organic fertilization
technique. Farming practices and methods should be suited to the
specific needs, limitations, resource bases and economic
conditions of the different farms. Therefore, different approaches
on organic farming would depend on farmers’ field conditions.
The documentation indicates that organic farming systems can and
do work and that they have a place in our drive for sustainable
agriculture. These different on-farm trials would only provide
insights and ideas for other farmers in developing their farm
similar to the organic farmers. This research was done primarily
to trigger their imagination and make them aware that sustainable
organic integrated system is possible and very profitable.
Basilio C S et al (1997) "Assessing the Viability of
LEISA Systems in Irrigated and Rainfed Lowland
Areas." Paper presented to the National Workshop on the
Development of Sustainable Agriculture Indicators: Case Study
Presentation and Analysis held at SEARCA Headquarters, College,
Laguna on December 16-17, 1997.
Cosico W C (1985) Organic Fertilizers: their nature, properties
and use, A publication of Farming Systems and Soil Resources
Institute, UPLB, Laguna. pp 6-15; 61-73; 91-98.
Dhanyadee P, Wassanan P, and Sombatpanit (n.d.) Fertility
status and recommendations for improving soil productivity in Thailand. (IN)
Cook H F and Lee H C (eds.) 1993, Soil Management in Sustainable
Agriculture. Proceedings of the Third International Conference on
Sustainable Agriculture held in Wye College, University of London
on 31 August to 4 September 1993, pp. 133-139.
Development Cooperation (1993) Sustainable Land Use, Sectoral
policy document no. 2, Ministry of Foreign Affairs, The
Netherlands.
Murakami S (1991) Lessons From Nature, A guide to
ecological agriculture in the tropics, PROSHIKA, Bangladesh.
Nartea R N (1990) Basic Soil Fertility, UP Printery Diliman,
Quezon City, pp. 139-182.
Pacturan et al. (n.d.) Sustainable upland farming
in Cagayan de Oro, Misamis Oriental ANGOC
Resource Book I : Community Initiative on Alternative Agriculture
Systems.
Patriquin D G, Baines D, and Abboud A (n. d.) Soil
Fertility Effects on Pests and Diseases (IN) Cook
H F and Lee H C (eds.) 1993, Soil Management in Sustainable
Agriculture. Proceedings of the Third International Conference on
Sustainable Agriculture held in Wye College, University of London
on 31 August to 4 September 1993, pp. 161-171.
Perlas J N III (1994) Bio-dynamic Vegetable
Farming, A training Manual, Quezon City, Philippines, pp. 10-19;
34-62
Reijntjes C, Haverkort B and Waters-Bayer A (1992) Farming
for the Future, An Introduction to Low-External-Input and Sustainable Agriculture, The
MacMillan Press Ltd., London.
SIBAT (1993) Sustainable Agriculture as practiced by farmers in
the Philippines (Case Studies), SIBAT National Secretariat, Quezon
City,133 p.
United States Department of Agriculture (1980)
Report
and Recommendations on Organic Farming.
Viado M F P (1997) Routing Sustainable Agriculture
Volume 1, Institute of Philippine Culture, Ateneo De Manila
University, Quezon City.
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