Abstract The effect of straw mulch, annually applied at rates of 0, 1, 2, 4 and 8 t/ha, was studied in 1967–1978 during three complete cycles of a 4-course rotation “summer fallow—3 times spring wheat”. Under the semi-arid steppe conditions of Northern Kazakhstan, mulching of the calcareous silty clay loam southern chernozem soil resulted in greater accumulation and conservation of plant-available moisture and reduced soil temperatures. After 12 years the organic matter content in the 0–10 cm layer increased by 0.17 and 0.58% for straw mulch rates of 2 and 4 t/h, respectively. The 9-year average grain yields of spring wheat were 1.41, 1.52, 1.54 and 1.61 t/ha for straw mulch rates of 0, 1, 2 and 4 t/ha, respectively. During cold and wet weather in the growing period of 1972 straw mulching had a negative effect on wheat yield.