Penetration resistance of gypsiferous horizons

Summary To assess the importance and the possible causes of penetration resistance of horizons with gypsum, 20horizons in seven irrigated profiles were studied. Gypsum contents ranged from 0 to 900 g kg –1 .Penetrometer tests were performed on undisturbed soil cores by means of a needle penetrometer atdifferent matric potentials. The increase of penetration resistance on drying was caused by changes inthe effective stress of the soils, calculated from their soil water characteristic curves. Multiple regressiontests showed that besides water content and bulk density, gypsum content was positively correlated withpenetration resistance. It seems that in the soils studied the increase of penetration resistance caused bygypsum is due to the growth of gypsum crystals in pre-existing pores, which reduces the volume ofregular and continuous voids necessary for root growth. Introduction mainly along cracks or horizontally at the top of the horizon(Poch, 1992).Soils with gypsum are found in several countries, especiallyThe objectives of this research were to identify factorsin Northern Africa, the Near and the Middle East and otheraffecting the penetration resistance of soils containing gypsumarid and semiarid areas where a sustainable agriculture isand to assess the importance of the penetration resistance ofneeded (FAO, 1990). Although they have been the object ofthese soils for root development.many investigations, mainly in relation to soil survey, soilgenesis and irrigation, little attention has been given to thecharacteristics affecting plant development, and even less to