3.2.1. Tillage effect on maize PSE and SWSp
We gathered 76 paired observations for PSE, and 139 paired observations SWSp (Figures 4a and 4b). As perceived by high Qt values of 73 and 133 for PSE and SWSp, the data showed strong heterogeneities. Compared to CT, conservation tillage methods generally enhanced PSE by 38.1% (P ≤ 0.05) (Figure 2a). The highest increase in PSE was perceived with NT (45.7%) followed by ST (14.9%) (P ≤ 0.05). PSE increased by 28% in medium-textured soils and 17% in both fine and coarse-textured soils under conservation tillage methods compared to conventional tillage. Compared to CT, the RR of conservation tillage on PSE was greater in the regions having MAP <400 mm. Conservation tillage also increased PSE in the regions where MAT was 8-15 ℃ (Figure 5a).
Overall SWSp was enhanced by 20.6% in comparison to CT (P ≤ 0.05, Figure 4b). However, the beneficial impact on SWSp differed according to the tillage techniques. In comparison to CT, SWSp increased by 36.1% under NT, 3.8% under RT and 4.9% under ST (P ≤ 0.05). In all soil textures, the RR of SWSp under conservation tillage methods to CT was favorable (Figure 5b). SWSp increased by 26.4% in fine-textured soils, while PSE increased by 22.2% and 17.1% in medium and coarse-textured soils, respectively. When MAP was 400-600 mm, the RR of conservation tillage on SWSp was higher compared to CT. Additionally, conservation tillage raised SWSp in areas where MAT was between 8 and 15 ℃.
3.2.2. Tillage effect on maize grain yield, ET and WUE
Overall, 158 observations were measured for grain yield, 97 for ET and 58 for WUE. Data was heterogeneous for yield (Qt = 154), ET (Qt = 89) and WUE (Qt = 52) (Figures 4c, 4d, and 4e). Conservation tillage methods increased grain yield by 29.6% compared to CT (P ≤ 0.05 , Figure 4c). The categorical meta-analysis showed that NT, RT and ST increased grain yield by 33.1%, 23.8 and 21.2%, respectively. The RR of yield under conservation tillage methods was positive in all soil textures (Figure 5c). Coarse-textured soils increased yield by 25.5%, while fine and medium soils increased grain yield by 11.1% and 16.2%, respectively. Compared to CT, the RR of conservation tillage on grain yield was greater when MAP was <400 mm. Conservation tillage increased grain yield when MAT was >15 ℃ (Figure 5c).
There was a significant effect of overall conservation tillage methods on crop ET. The NT, RT and ST increased spring maize ET by 10.1% and 14.7% and 16.8%, respectively (P ≤ 0.05 , Figure 4d). Medium-textured soils increased ET by 18% while fine and coarse textured-soils enhanced ET by 12.0% and 9.7%, respectively. Compared to CT, the RR of conservation tillage on ET was greater when MAP was <400 mm. Conservation tillage also increased ET in the regions where MAT was <8 ℃ than >15 ℃ and 8-15 ℃ (Figure 5c).
Maize WUE increased by 11.0% with overall conservation tillage practices (P ≤ 0.05 , Figure 4e). The NT, RT and ST increased WUE by 19.4%, 3.1% and 10.7 %, respectively. Maize WUE increased with conservation tillage during fallow period in all soils, but the effect of conservation tillage methods was more prominent in medium-textured soils with an increase of 21.3% (Figure 5e). Compared to CT, the RR of conservation tillage on WUE was greater when MAP was <400 mm. Conservation tillage methods also increased WUE when MAT was >15 ℃ (Figure 5c).
Discussion