MODIFICATION OF SOIL AGGREGATION BY WATERING REGIME AND ROOTS GROWING THROUGH BEDS OF LARGE AGGREGATES

The influence of root growth and soil watering regime on aggregation was studied under controlled conditions. The study examined the influence of pea (Pisum sativum cv Greenfeast), ryegrass (Lolium rigidum cv Wimmera) and wheat (Triticum aestivum cv Kite) roots on changes in aggregation and on the properties of the aggregates. The soil was a non swelling red-brown earth which was either kept wet or was allowed to wet and dry during the experiment. Root growth increased the percentage of small sized aggregates (<18 mm diameter), organic carbon, tensile strength and stability of aggregates in comparison with a non planted soil. Changes in aggregate size distribution and properties of the aggregates were related to root length density of the species and also to the soil watering regime. Root length density was in the order ryegrass > pea > wheat. Wetting and drying of soil increased the strength and stability of aggregates. Incubating aggregates allowed some roots to decompose but did not increase the strength or stability of aggregates compared with unincubated soil. The results of this experiment are of practical significance in soil structural management, and in studies of soil aggregation dynamics. It may be possible to use plant roots to alter the size and properties of aggregates.