treatments. They attributed the reduction of rice yield to a low
depth of puddling and high sinkage resistance that reduced root
growth. The maximum penetration resistance in the plough layer
was 1200 kPa under DT and 2200 kPa under ST. Crop root growth
may be reduced by 20% to 75% when penetration resistance
increases to 1500 kPa (Bengough, 1997), but the limit of penetration resistance varies with crop type (Bengough et al., 2011).
Although the difference in rice yield between C1 and C2 (Fig. 1) can
be attributed to the difference of nutrient inputs from rice straw,
the lower root weight and the longer root length in C1 than in
C2 particularly in the deeper depth of the plough layer under ST
suggested that the root growth may have been impeded by the
increased sinkage and penetration resistances.