In the experiment with subsoiling, the effects of the pressures applied on the sowing furrow on the increase of RP were more evident (Figure 2A); in the experiment without subsoiling, the effects of pressure on RP were similar (Figure 2B), possibly for being under greater compaction compared with the soil under subsoiling, which caused it to resist to the pressure exerted on the sowing furrow.
Considering the layer of 0-0.20 m, in which most rice roots are concentrated (Stone & Pereira, 1994), RP showed maximum values around 2,200 and 3,200 kPa, respectively for the experiments with and without subsoiling. These values probably did not damage the crop, because the RP values that restrict root growth or crop yield are close to 3,000 kPa (Reichert et al., 2007).
Subsoiling positively affected rice yield in the presence of higher compaction pressures on the sowing furrow.
The PUE at moderate level of N was highest while lowest efficiency was found at low level of N (Table 6) indicating that subsoiling combined with application of 150 kg hm-2 N was optimum.
Table 3: Effects of subsoiling and nitrogen fertilizer on soil water storage in the 0-300 cm depth at different growth stages of dry-land wheat
Table 4: Effect of subsoiling and nitrogen fertilizer on yield and its component of dry-land wheat
This result showed that the interval with no-tillage and subsoiling could effectively retain soil water from rainfall during July-September.
This was because the interval with no-tillage and subsoiling would have decreased soil bulk density (Qin et al.
No-tillage coupled with subsoiling could make full use of summer rainfall, retain water in deep soil, and meet the needs of summer and autumn crop growth in dry years or normal years (Qin et al.
In that study, all treatments received in-row subsoiling, and corn grain yields were not significantly different between conventional disked or non-disked surface tillage treatments.
In the absence of subsoiling, the importance of partially ameliorating plant rooting problems with the higher organic matter and nitrogen contents of no-till is shown.
Over that period, the mean yield for the treatments with no surface tillage and in-row subsoiling was 5.23 Mg [ha.sup.-1] with a range of 1.06 to 8.02 Mg ha-l; similarly, the mean for treatments receiving both surface tilled and in-row subsoiled was 5.30 Mg [ha.sup.-1] with a range of 1.29 to 7.48 Mg [ha.sup.-1]