2.1 Soil-related constraints. Crop yields are affected by the following soil-re
lated factors:
i) Soil degradation: due to water logging in the backswamp areas; sali
nization in estuary zones or in dammed areas, acidificatlon and irre
versible changes in physical properties (physical degradation) as in
the case of drying acid-sulfate or peat soils, etc.
ii) Decrease in soilfertility: due to decrease in soil organic matter c
ontent, soil nutrient status, changes in soil fauna (earthworms, mic
robes), etc.
iii) Nutrient imbalance in the monoculture soils: too much nitrogen (N)
while deficient in phosphorus (P) and/or potassium (K); or deficient
in sulfur (S), zinc (Zn), iron (Fe), etc.
2.2 Water-related constraints.
i) Quality: irrigation water becomes more and more saline due to seawat
er in-trusion as a result of excessive upstream abstraction; brackis
h water Is used for irrigation due to less and less availability of
good water.
ii) Quantity: irrigatlon water for agriculture will be less due to comp
eting de-mands for water from industry, domestic service, etc. in th
e urban areas; lowerlng of ground water table due to over pumping; e
tc.
iii) Management: drainage problem; Inefficient on-farm water use; etc.
2.3 Build-up of biotic stress'es: because a large number of farmers applying to
o many kinds of pesticides at the wrong time and wrong doses, they uncon-sc
lously killed friendly insects and instead created favorable conditlons for:
i) Resurgence of pests and diseases
ii) Minor pests, including weeds, becoming major pests.
2.4 Variety degeneration: crop varieties, specially rice, after years of uses w
ithout technical care in purification, may become mixed with off-types. The
resulting seeds became unsuitable due to:
i) Low seed quality and inapproprlate handling;
ii) Breakdown of varietal resistance/tolerance to a pest due to evolutio
n of new biotypes.