Fig. 8
There was a significant quadratic relationship between MAT and maize yield under NT (R2 = 0.408, P < 0.001, Fig. 8a) and RT (R2 = 0.576, P < 0.001, Fig. 8a), with yield peaking at ~6.5 °C in both treatments before declining. In contrast, a negative linear relationship was observed for ST treatments (R2 = 0.335, P = 0.001, Fig. 8a). There was also a significant positive linear relationship between maize yield and MAP under NT (R2 = 0.089, P=0.035), and a quadratic relationship under ST (R2=0.51, P<0.001), although no significant relationship between maize yield and MAP was observed for RT (Fig. 8b). However, under high MAP condition (~700 mm) little difference was observed among the three conservation tillage measures (Fig. 8b).
No significant relationships were observed between soybean yield and MAT or MAP. However, there was a trend for a negative linear relationship between yield and MAT under NT and RT, and a positive linear relationship under ST (Fig. 8c). There was also a trend towards a positive linear relationship were between soybean yield and MAP for all tillage treatments (Fig. 8d).
The SOC concentration at 0-20 cm under NT (R2 = 0.758, P < 0.001), RT (R2 = 0.932, P < 0.001) and ST (R2 = 0.655, P = 0.027) decreased with increasing MAT (Fig. 9a). But the change in SOC as MAT increased above 7°C was minimal. A quadratic relationship was observed between SOC and MAP for NT (R2 = 0.293, P = 0.003) and ST (R2 = 0.886, P = 0.013) treatments, with SOC peaking at ~ 600 and 500 mm in NT and ST treatments, respectively, before declining (Fig. 9b). A significant positive linear relationship was observed between SOC and MAP for RT treatments (R2 = 0.762, P < 0.001), although only limited datapoints (MAP range from ~500 to ~550 mm) were available, and further data is needed to confirm this relationship.