4.2. Effects of conservation tillage methods on spring maize
Compared to CT, conservation tillage methods also increased spring maize PSE, SWSp, grain yield, ET and WUE by 38.1%, 20.6%, 29.6%, 16.9% and 11.0%, respectively (P ≤ 0.05 Figure 4) which corresponds to the results obtained by Li et al. (2007) and Heet al. (2009) who stated that conservation tillage methods are effective in improving soil water storage and crop yield. Among conservation tillage methods, the highest PSE (45.7%) and SWSp (36.1%) were observed with NT (Figure 2) which confirms our 2nd hypothesis (such as the highest PSE under wheat cropping system was obtained by RT, Figure 2) that the effects of conservation tillage methods will differ among winter wheat and spring maize cropping systems, that corresponds to (Jin et al., 2007) who found that NT is the best tillage practice in fallow period for water conservation with the effective storage efficiency of rainwater (Figure 4). Similarly, highest increase in maize yield (33.1%) and WUE (19.4%) were obtained by NT and is corresponding to the results of Li et al. (2007) and He et al. (2009) who stated that conservation tillage methods are effective methods and can reduce soil compaction, improve soil structure which eventually increase yield and WUE (Pikul Jr and Aase, 1999; Pikul and Aase, 2003). Previous studies in the Loess Plateau also reported higher water content and yield with conservation tillage methods during fallow period compared to CT Liang et al. (2002) and Wang et al. (2003), which is consistent with the results found 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 (Lenssenet al., 2007), semi-arid Kenya (Gicheruet al., 2004).