Soil Inherent and Extrinsic Properties Effects on Erosion: A Systematic Laboratory Study.

Soil loss and pollution in agricultural watersheds by water erosion requires understanding and evaluating the temporal and spatial impacts of the processes involved. We have studied in a systematic manner, using a laboratory rainfall simulator, the contribution of soil inherent properties and extrinsic conditions on soil erosion from numerous soils (~60) collected from the top cultivated layer. The studied soil inherent properties included: (1) predominant
clay mineralogy (kaolinitic, illitic and smectitic); (2) soil texture (4-6 typical textural class from sandy to heavy clay); and (3) organic matter content. The studied extrinsic conditions included: (1) 4-5 levels of rain kinetic energy (KE, 0-22 kJ/m3); (2) 3-4 wetting rates (WR) of dry soil by rainfall and irrigation water; (3) water quality (rain and fresh, saline, or waste irrigation water); (4) 4-8 antecedent moisture content levels (from dry to full saturation) and aging durations between two wettings; (5) type of tillage (conventional and no-ill); and (6) soil salinity, and sodicity, and use of soil amendments (polymer, gypsum, manure). Results showed that (i) soil erosion increased exponentially with the increase in rain KE and WR of soils and soil sodicity. Rain KE and water quality predominate in determining
soil loss in medium- and light-textured soils, and WR predominates in controlling soil loss in heavy-textured soils (> 40-70% clay); (ii) in the moisture range between wilting point and field capacity (pF 2.7-4.1), soils from semi-arid region, particularly clay soils, had the lowest sediment losses; (iii) in soils with <20% clay, prevention of physicochemical clay dispersion by gypsum application is preferable in controlling soil erosion, whereas in clay soils, prevention
of aggregate slaking during the wetting process of the soil could be more beneficial; the effect of WR on soil loss increased extensively with the increase in clay content; (iv) no-till caused a greater impact on increasing erosion, mostly for soils with 2:1 clay mineralogy; (v) a small application of dry granular polymer in combination with gypsum may effectively decrease sediment losses by up to 2-4 times relative to control, mostly in smectitic and illitic soils. Whereas the inherent soil properties cannot be changed, conditions prevailing in the soil such as soil WR, moisture content, impact of rain kinetic energy, etc. on soil erosion can be controlled by certain management practices (minimum till or no-till with known residue level, irrigation, amendments) to maintain adequate conditions that decrease soil susceptibility to  erosion. The results of our study help to better understand the change in potential erosion rates in arid- and humid-zone soils and could be useful for predicting soil erodibility and nutrient loss by erosion.