4.4. Correlations of wheat and maize grain yield, ET and WUE to SWSp
The RR of wheat and maize grain yield increased linearly with increase of the RR of SWSp for conservation tillage practices (Figure 6). An increase of 24.1% in wheat and 29.6% in maize yields can be explained by the increase of the RR of SWSp for conservation tillage practices. The RR of ET to SWSp under conservation tillage methods was significant for wheat but remained non-significant for maize. Similarly, the RR of wheat and maize WUE was also related to with that of SWSp, which can be attributed to 12.1% increase in wheat and 11.0% increase in maize WUE under conservation tillage methods (Figure 6).
Conclusion
The meta-analysis results showed that conservation tillage methods overall increased soil water storage, grain yield and crop water use in both winter wheat and spring maize cropping systems compared to conventional tillage. Although overall conservation tillage methods increased PSE, SWSp, grain yield, ET and WUE in both of the cropping systems but the intensity was greater in spring maize as compared to winter wheat. Soil texture and precipitation pattern played a significant role in determining the results. High precipitation increased PSE, SWSp and wheat grain yield and the effect was opposite in case of maize. Fine-textured soil increased PSE, SWSp and ET in both of the cropping systems while medium-textured soil showed increased grain yield and water use in both cropping systems. Even though different conservation tillage methods had variable effects on soil water conservation under different edaphic and climatic conditions, however, overall conservation tillage methods can improve soil physical health and enhance crop productivity to obtain food security under climate change scenario.