Drought Resistance of Cover Crops and Grain Crops in Oxisols in Southern Brazil

The lower limit of available water, usually considered the permanent wilting point, can be influenced by soil attributes and by the specific ability of plants to use retained water at low soil water potentials (Ψ_m). This study evaluated the Ψ_m at which the physiological permanent wilting point (Ψ_PPWP) of different crops occurs to identify the species most resistant to water deficit. The Ψ_PPWP of three grain winter crops (wheat, barley, and rye) and three autumn cover crops (black oat, forage turnip, and vetch) were evaluated in two Oxisols, one sandy-clay and other very clayey soil. The water content in the Ψ_PPWP was measured with a dew point potentiometer. The plants wilted at Ψ_m ranging from − 35,900 to -79,540 hPa in the very clayed Oxisol, and from − 26,840 to -99,060 hPa in the sandy-clay Oxisol. The resistance of plant species to water deficit decreased in the following order barley = black oat > vetch = wheat = rye > forage turnip in the very clayey soil and barley = black oat > vetch > wheat = forage turnip > rye in the sandy-clay soil. We found a significant correlation between the root dry matter/shoot dry matter ratio and Ψ_PPWP, indicating that the roots produced by the plants exerted influence on resistance to water deficit. Barley (cash crop) and black oat and vetch (cover crops) stood out for their greater resistance to water stress.