Responses of a root system structure to soil compaction stress among maize (Zea mays L.) hybrids

Effects of soil compaction stress were investigated in maize hybrids subjected to low (L-1.10), medium (M-1.30) and high (H-1.60 g/cm(3)) soil compaction. The hybrids selected for the study differed in their susceptibility to growth under soil compaction stress conditions. We used appropriate methods of non-destructive cleaning and analysis of all intact compartments of the root system. Petrolatum-wax test, proved as an effective screening technique for selecting resistant and sensitive maize hybrids, was also employed. The seedlings were grown in custom-made 'root-box' and 'root-basket' containers. The penetration resistance (PR) strength of 0.52 and 1.07 MPa was satisfactory for estimating root penetration index (RPA) among maize hybrids. The soil compaction stress affected root system structure (RSS) in maize hybrids. The resistant hybrids showed a lower decrease in root dry matter (DM) in M and H treatments at 0.0-15 cm soil depth, and an increase in the number of roots growing at an angle of 0 degrees-30 degrees in relation to the main growth axis, comparing to sensitive hybrids. The soil compaction stress lowered root number (R-N) and length (R-L), shoot and root DM, and increased shoot to root ratio (S/R). The changes were greater in sensitive than in resistant hybrids. In addition, a regression coefficient (R-2) between stress susceptibility index (SSI) and relative trace change (RTC) marked for changes in dry matter of shoot (S), roots (R), shoot to root (S/R) ratio and root length (R-L) and number R-N was statistically significant. Seedlings of maize single-cross hybrids demonstrated differences in their responses to soil compaction stress, which caused changes in shoot and root dry matter and the distribution of roots in the soil profile.