Testing gypsum suspension and Polysulphate to improve soil hydraulic properties

Dr. Meni Ben Hur and Dr. Uri Nachshon
Start: Jun 2016 –  End: Jun 2019

General: ICL labs developed a suspension of gypsum particles with 50 μm size. The aim of this suspension is to improve water penetration and infiltration in cultivated lands. The first step in the present research will be evaluating the efficiency of using the gypsum suspension and to compare it to the common practice of spreading solid gypsum in agricultural lands to improve soil hydraulic properties.

Theory: A common practice to improve soil hydraulic properties in cultivated lands is applying solid (crashed) gypsum at the fields. In addition, the gypsum may add Ca, which is an important nutrient for plants, to the soil solution.

The two major reasons that responsible to soil hydraulic properties deterioration in cultivated lands are:

1. Formation of a thin and dense soil crust with low hydraulic conductivity at the soil surface 1. The crust formation is caused by the kinetic energy of rain and irrigation (sprinklers) water drops that mechanically break the soil aggregates at the soil surface. In addition, the low electrolytes concentrations of the rainwater may lead to clay dispersion, and these dispersed clay particles could clog the soil pores, leading to further reduction of the hydraulic conductivity of the crust 1–3. The crust formation leads to a reduction in the infiltration rates and increasing in surface runoff and soil erosion amounts, and loss of adequate water that could be used by the crops. Soils with high exchangeable sodium percentage (ESP) are particularly susceptible to significant breakdown of their structure and to crust formation due to the low flocculation value of the clays in these soils 4. In Israel these processes are very common in the loess and gromosol alkaline soils of the north western Negev and in Izrael valley region. The common practice to cope with this problem is by spreading 5-10 Mg/ha of solid gypsum on the soil surface. The rain and irrigation water dissolves the gypsum, increasing electrolytes concentration in the soil solution and consequently decreasing clay particles dispersion and the formation of the impermeable crust 2.
2. Destruction of soil structure at the root zone mainly due to swelling and dispersion of clays in sodic soils. Increasing of soil ESP results in increasing of the negative chemo-electric.