Determination of soil surface strength with a needle-type penetrometer

Soil crusting was characterized by means of direct measurement of penetration resistance with a needle type penetrometer at intervals of 0.1 mm over a depth of 15 mm in intact soil samples, treated with soil stabilizers or not, as a function of soil water content and bulk density. Relationships were established between the penetration resistance of the needle and standard cones of 60° angle and 1 cm² or 26.4 mm² base area. The effect of water content was stronger in dense than in loose soil.The effect of soil surface strength on the emergence of salsify (Scorzonera hispanica) was monitored in a field experiment on a loamy sand of which the natural crust was stabilized with soil conditioners. The penetration resistance was affected by the nature of the soil stabilizers as some created more or less hydrophobic and spongy crusts. Seedling emergence was negatively correlated with the penetration resistance and positively with the water content of the crust.