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Clay, Calcium Carbonate, and Sodium Polymetaphosphate Interactions in Soil Seal Formation

* Corresponding author.

ABSTRACT

The objective of this study was to investigate the interactive effects of sodium polymetaphosphate (NaPMP), CaCO₃, and clay contents on seal formation and runoff. The NaPMP was applied in concentrations ranging from 0 to 300 kg ha^–1 on calcareous and noncalcareous soils with clay content from 4 to 60%. Infiltration rates (IR) of these soils were measured by a rainfall simulator. Seal formation and amount of runoff increased with increased dispersant to an optimal value, above which more dispersant was not effective. Interaction between clay content and NaPMP was found; however, none was found between CaCO₃ and NaPMP. In soils with approximately 20% clay content the NaPMP had no effect on seal properties, but did have an effect on the rate of seal formation. In soils with < 20% but > 7% clay content, the effect of NaPMP on the seal properties and its rate of formation increased as the clay percentage decreased. The lower the clay content in the soil, the more dispersant was needed. Conversely, the amount of NaPMP needed to form a seal in soils with > 20% clay increased with the amount of clay. In these soils since aggregate stability increases with clay content, the amount of NaPMP needed for dispersal correspondingly increased. In sandy soils, the amount of clay was not sufficient for seal formation and high infiltration rate (IR) was maintained. The NaPMP application in these soils increased the clay dispersion, which allowed clay particle migration through the sandy soil (0.2-m layer).

Contribution from the Agricultural Research Organization (ARO), The Volcani Center, Bet Dagan, Israel. No. 2308-E, 1988 series. Inst. of Soil and Water, ARO, The Volcani Center, Bet Dagan, Israel.

Received for publication March 17, 1988.