A b s t r a c t. This greenhouse research was carried out to study the effects of water and tillage erosion on agricultural productivity and soil quality in soil samples from a semiarid region of Iran. A factorial experiment of complete randomized block design was used to compare the effects of soil erosion (eroded and non-eroded soils), slope position, water stress and fertilizer (N-P-K) on yield and yield components of wheat as soil productivity index. The results showed that erosion ie water and tillage erosion has a significant effect (p<0.01) in decreasing soil productivity due to its negative impact on soil organic matter, nutrients (N and K) and hydraulic conductivity. Complete N-P-K fertilization and water stress had significant effects on increasing and decreasing of wheat yield, respectively. The effect of water stress in particular was so high that it could eclipse the erosion impact on yield reduction. Wheat dry matter and grain mass on foot and mid slopes were significantly higher than that on upslope positions where total N and available K were the lowest and equivalent calcium carbonate the highest. Saturated hydraulic conductivity and total nitrogen were found to be the most important soil properties as far as their correlations to wheat yield are concerned.K e y w o r d s: slope position, greenhouse experiment, wheat, fertilizer, water stress INTRODUCTIONMore than 60% of Iran farm lands are under dryland farming of wheat, barley and other cereal crops. The area under dryland farming of wheat alone is around 4 to 5 mln ha (Agricultural Statistics of Iran, 1998). A large fraction of Iran cultivated lands (dryland and irrigated) is devoted to wheat and barley which are the main sources of staple food and protein for the average Iranian. Wheat alone covers about one third and fruit tree plantations cover nearly one fifth of the total irrigated lands of Iran. Cereal crops ie wheat, barley, and rice) cover almost 70% of the cultivated land, while wheat alone covers nearly 52%. In Iran, it is a well established fact that the average yield of different crops is much higher under irrigated system than under dryland farming. For example, the average yield of irrigated wheat is about 3 200 kg ha -1 while under dryland farming this figure is below 1 000 kg ha -1 (Siadat, 1998).Erosion is very severe in the semiarid and drylands regions of Iran due to high erodibility of the soil and poor vegetation cover. The increasing population and the need for more food and fibre have pushed farmers to use lands which are not suitable for farming, especially on steep slopes (Ahmadi-Iikhchi et al., 2003). Many grasslands have also been destroyed due to high stocking rate and over-grazing, resulting in severe soil degradation (Asadi et al., 2012).Soil erosion, in the form of mass downslope transport, is also intense under the conventional tillage systems which employs the mouldboard plough (Alvarez et al., 1995), still the most common form of tillage in Iran. On-site impact of accelerated soil erosion includes short-time ...