The soil water potential at field capacity varies from soil to soil, and it generally ranges from –10kPa (sandy soils) to –33kPa (clayey soils). Usually, soil attains field capacity 2 to 3 days after irrigation or rainfall. Field capacity is determined in the field by flooding water in an area of 2 to 5 m2, and allowing it to drain for 1 to 3 days after preventing surface evaporation using polythene sheets or thick straw mulches. After this time, soil samples are collected from the wetted zone, and the moisture is determined by the thermo-gravimetric method.

Not much differences in moisture percentages has been observed regardless of the potential at field capacity between soils. Therefore, in laboratory analysis, especially when using a pressure plate apparatus, the moisture percentage of soil at 30kPa pressure is commonly taken as field capacity.

We need to use soil moisture retention characteristic curve in relation to different soil textural classes as a most practical tool box to ward off any potential behavior differences out of soil textural variation.

iN THE field determination and Laboratory MATRIC POTENTIAL OF 10 kPA

The soil water potential at field capacity varies from soil to soil, and it generally ranges from –10kPa (sandy soils) to –33kPa (clayey soils). Usually, soil attains field capacity 2 to 3 days after irrigation or rainfall. Field capacity is determined in the field by flooding water in an area of 2 to 5 m2, and allowing it to drain for 1 to 3 days after preventing surface evaporation using polythene sheets or thick straw mulches. After this time, soil samples are collected from the wetted zone, and the moisture is determined by the thermo-gravimetric method.

Not much differences in moisture percentages has been observed regardless of the potential at field capacity between soils. Therefore, in laboratory analysis, especially when using a pressure plate apparatus, the moisture percentage of soil at 30kPa pressure is commonly taken as field capacity.

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