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.