Fig. 3
In cold areas (MAT < 3 ℃), yield under NT was significantly lower than CT as well as ST (P < 0.05), with yield reductions of 3.7% compared to CT (Fig. 3a). Under warmer temperature regimes (MAT > 6 ℃), crop yield under NT was increased by 13.1%, which was significantly higher than NT in colder areas (MAT < 6 ℃) (P < 0.05). RT showed a similar trend to NT as MAT increased, but yield effect under RT was above 0 all the time, which indicated a trend for better yields under RT compared to NT under cooler temperatures (Fig. 3a).
NT had a negative effect on yield (P < 0.05) when MAP was 500 - 600 mm, with crop yield reduced by 1.4% compared to CT (Fig. 3b). However, when MAP was either < 500 mm or > 600mm, NT had a positive impact on yield (P < 0.05). Under a rotational cropping pattern, crop yield decreased by 0.5% under NT and increased 1.9% under RT compared to CT, but both of them were significantly lower than that under ST (P < 0.05), which increased 16.7% compared to CT (Fig. 3c). Under a continuous cropping pattern, all the conservation tillage measures improved yield relative to CT, but the difference among them was not significant (Fig. 3c). As the period of experiment duration increased, the yield effect with conservation practices also tended to increase, although this was only significant for ST. When duration > 8 yrs, the difference between NT and other tillage practices was not significant (Fig. 3d).
3.2. Effects of Conservation Tillage Practices on SOC Concentration