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).