[Effect of soil bulk density on maize growth under different water regimes]

Split-root experiments were conducted with maize under both low (-0.86 MPa) and high (-0.17 MPa) soil matrix potential conditions, in which, maize roots were divided equally between two compartments in partitioned galvanized steel containers containing Lou soil. Four treatments were installed, i.e., low bulk density (both compartments packed to 1.2 g.cm-3), medium density (both compartments packed to 1.33 g.cm-3), high density (both compartments packed to 1.45 g.cm-3), and mixed density (one compartment packed to 1.2, the other to 1.45 g.cm-3). The results showed that high soil bulk density and low matrix potential had a significant effect on root and shoot growth, but the effect of low matrix potential was more profound. There was a significant decrease in root dry matter and shoot dry weight, but the shoot growth was reduced more significantly than root growth, when the plants were grown on compacted soils or the soil matrix potential reached -0.86 MPa from -0.17 MPa. Both leaf expansion rate and plant size reductions occurred under high soil mechanical resistance caused by increased bulk density or lowered soil water content. The smaller size of plants in compacted treatments was due to the reduced leaf expansion rates and the smaller maximum size of individual mature leaf. In contrast, when plants were grown in soil with mixed bulk density, there was an enhanced growth of root in low-density soil to compensate or even overcompensate the reduced growth in high-density soil, and hence, the plant growth was comparable with that in low bulk density soil.