4.1. Effects of conservation tillage methods on winter wheat
Averaged across all locations, conservation tillage methods overall increased winter wheat PSE, SWSp, grain yield, ET and WUE by 22.6%, 17.8%, 24.1%, 6.5% and 12.1%, respectively (P ≤ 0.05 Figure 2) which corresponds to a recent meta-analysis by Adil et al. (2022) that described the positive effects of conservation tillage methods and fallow mulching in dry lad cropping systems, and also to the results obtained by Li et al., (2007) who described that conservation tillage methods are effective in increasing soil water storage and crop yield. The positive effect of conservation tillage methods on soil water storage compared to conventional tillage clearly confirmed our 1st hypothesis that conservation tillage methods will improve soil water storage during fallow period which is probably due to the reduced soil disturbance, reduced soil bulk density and improved aggregate stability by NT (Oyedeleet al., 1999; Zhang et al., 2007). Similarly, conservation tillage methods are effective conservation tillage methods (Li et al., 2007; He et al., 2009) that reduced the soil compaction, improved soil structure which eventually increased yield and WUE (Pikul Jr and Aase, 1999; Pikul and Aase, 2003). Moreover, previous studies in Chinese Loess Plateau also reported higher water content and yield with conservation tillage methods during fallow period compared to CT (Liang et al., 2002; Wang et al., 2003) and is consistent with the results of current meta-analysis that also corresponds to the previous studies conducted in other areas including Victoria (Australia), Nebraska (USA) (Lyon et al., 1998; Cantero-Martinez et al., 1999), and Texas (USA) (Baumhardt and Jones, 2002), Great Plains of the Northern USA (Lenssen et al., 2007), semi-arid Kenya (Gicheru et al., 2004).
In our study, RT increased wheat PSE by 25.1% compared to CT and this effect was slightly more than that of ST (23.9% increase compared to CT) (Figure 2). ST had good results than CT may be due to the deep loosening of the soil which resulted in better infiltration and the breaching up of the permanency of flow paths in the soil (Hillel, 1998). Although, NT increased PSE by 10.9% compared to CT (Figure 2), which is in accordance with (Halvorson et al., 2000) who described the effect of NT and CT under dry conditions. In our study, 24.1% increase IN wheat yield was obtained with NT compared to CT and the similar results were obtained by Jin et al. ( 2007) who described that after 6 years of experiment, NT showed highest yield by improving soil physical and chemical properties and stabilizing the bulk density of soil after 5 years of NT practice (Fabrizziet al., 2005).