Investigating the effect of wheat straw mulch on soil water retension in rainfed condition

Water deficit in arid and semi-arid regions is the major yield-limiting factor of crop plants in arid and semi-arid regions. So, prevention of water loss is the first major step to obtain proper crop yield in rainfed lands of these regions. This study was conducted to investigate the effect of mulch application on soil water retention under rainfed conditions in a semi-arid region. Toward this, five wheat straw mulch levels (0, 25%, 50%, 75%, and 100% of land surface cover) were used according to the randomized complete block designat three replications in a rainfed land with 10% steepness in Zanjan. About 6 ton straw mulch was used in 100% treatment. Fifteen plots with 2m×5m in dimensions were installed in the land and S was measured using the volumetric method in each mulched plot at 7-day interval during wheat growth period (from October 2015 to July 2016). Results indicated that SWR temporally varied during the growth period, so that the highest value of SWR in the mulched plots was observed in March, when the heavy rainfalls were occurred in the area. SWR was significantly related to straw mulch level (R2= 0.95, p< 0.001). Increasing SWR in the mulched plots was attributed with increasing soil water holding capacity. Application of straw mulch positively affected on the soil water holding capacity. The highest SWR was observed in 100% mulch (10.62%), about 11% more than that one in the contour plot. There was no significant difference between 75% mulch and 100% mulch in SWR as well as soil water holding capacity, so the application of 75% straw mulch can be considered as the optimum level for increasing soil water holding capacity as well as SWR in the rainfed lands of semi-arid regions.