Soil Organic Matter Management: The Roles of Residue Quality in C Sequestration and N Supply - Sustainable Management of Soil Organic Matter - page 194

The intrinsic sustainable fertility of traditional rice farming systems,
maintained by biochemical processes, will normally provide a low level
of yields, of the order of 2 t ha −1 (Giller and Wilson, 1991). Rice farming
systems in Bangladesh still rely substantially on returns of organic matter
and biological N fixation from blue-green algae to maintain their inherently
high level of fertility. PROSHIKA, a non-governmental organization, and
others promote 'ecological farming'. Their goal is to 'promote an ecological
agricultural system which is productive, equitable and cost effective'.
Farmers are taught that using no-tillage, mulches, compost and green
manures improves soil fertility. In principle, no chemical fertilizers or pesti-
cides are to be used. PROSHIKA provides motivation and formal training
to farmers, who then are encouraged to adopt ecological agricultural prac-
tices and pass on information to others.
Due to the shortage of fuel, farmers have to burn crop residues and
up to 80% of their cowdung (Parikh, 1988), whereas the landless will burn
all that their cow produces rather than using this manure to improve or
maintain soil fertility. Thus, in our experience, farmers rarely convert all
their fields to ecological management.
During field visits, farmers working with PROSHIKA suggested that
fields which they converted to ecological management practices were
more fertile. During discussions, they cited improvement in soil physical
properties, described as ease of ploughing and increased biological activity,
as indicators of these changes. This chapter seeks to see whether these
observations can be confirmed using established quantitative methods to
compare conventional farming systems that include chemicals with the
ecological farming system.
Materials and Methods
Four different village sites were located in the following thanas (smallest
administrative unit): Dhamrai, Daulatpur, Gabtali and Shibganj; the thana
name was used to identify the field sites. The field sites were chosen on
the basis of different flooding regimes and were located in two districts of
Bangladesh, Dhaka and Bogra. Dhamrai and Daulatpur represent lowland
areas (Dhaka district), which are subjected to flooding from the local rivers
during the monsoon season; flood depths range up to 2 m and both are
south of the Jamuna River. Gabtali and Shibganj represent medium high
land flooding conditions with flooding depths up to 1 m, mostly due to
rainwater flooding at the same time (June-September).
Ten fields were selected at random from an immediate village area for
each of the two farming systems, although the selection process depended
upon farmers following the necessary management system and being
willing to participate in the experiment. At Dhamrai, fields had been under