Monday, November 13, 2006

Response of Early Corn (Zea mays L.) Growth to Soil Aggregates.

Bandula Premalal and Bill Deen. University of Guelph, 50 Stone road, Guelph, ON N1G2W1, Canada


Corn (Zea mays L.), a major grain crop in Ontario, Canada, is grown using varied crop rotations and tillage systems. Corn yields vary across these systems and it is hypothesized that yield differences are in part due to direct effects of soil aggregate size distribution observed in these production systems, and/or indirectly due to their dependents such as availability of nutrients, water, oxygen, and soil temperature differences.  A growth room experiment was conducted to examine early season corn shoot and root growth response to different aggregate sizes. To eliminate confounding effects of moisture, oxygen and temperature, the experiment was conducted using a novel hydroponics system. Treatments consisted of no-mechanical stress (pure nutrient mixture), coarse aggregates (turface, 2-7 mm diameter) + nutrient mixture and fine aggregates (turface, <0.2mm diameter) + nutrient mixture. Pots were aerated continuously and nutrient mixture was circulated in such a way as to ensure uniformity and minimal interruption to growing roots. Effect of mechanical stress caused by aggregate size was observed at early stages of corn growth. Higher root dry weights were observed under no-mechanical stress (78%) and corn in fine aggregates (32%) when compared to coarse aggregates at 5-leaf-tip stage. Root characteristics were also different among treatments. Higher total root lengths were observed under no mechanical stress treatments (116%) followed by the fine aggregate treatment (44%) when compared to corn in coarse aggregates. However, these differences were less severe at 7-leaf tip stage and disappeared when corn seedlings reached 10-leaf tips. Results demonstrate the direct effects of mechanical stress imposed by aggregates when other factors are at non-limiting levels.