The experiment had four treatments: (i) deep ploughing with no plastic mulching (CK); (ii) deep ploughing with plastic film mulching (PM); (iii) buried straw layer at a depth of 40 cm with no mulching (SL), and (iv) buried straw layer at a depth of 40 cm plus plastic film mulching (PM + SL). The treatments were arranged into a randomised complete block design with three replications. Each plot measured 4 m2 (2 m _ 2 m), and was insulated by double-plastic sheets buried to a 100 cm depth relative to the soil surface to minimise the effects of lateral water and salt movement between plots. Each plot was surrounded by a concrete panel 40 cm wide and 60 cm high, and the exposed part of panel (approximately 20 cm) was hardened with cement. The upper 40 cm of soil in the SL and PM + SL plots was removed at intervals of 20 cm depth and placed in different positions before uniformly placing the (air- dried) chopped maize straw to a thickness of about 5 cm (equal to 12 t ha_1). The dug soil was refilled layer-by-layer and then flattened with a harrow to a bulk density consistent with the initial value. Plots were flood-irrigated in late October at approximately 0.6 m3 per plot. To leach soluble salts for sunflower (Helianthus annuus L.) germination in each growing season, a second irrigation (0.6 m3 plot_1) was applied approximately 10 d before sowing. The straw layer burying operation was done once at the beginning of the experiment.