Aggregate stability of a silt loam soil as affected by roots of corn, soybeans and wheat

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Abstract
A greenhouse experiment was conducted to investigate the effect of root growth and exudation of 3 crop species on soil aggregation. Two plant populations for each of 3 crops (corn, soybeans, and wheat) were grown in a Fincastle silt loam for 5 time periods (7, 14, 21, 28, and 41 days) and compared with fallow controls. Aggregate stability was estimated by the wet‐sieve method on both initially moist and air‐dry samples. Soil water content of initially moist soil samples varied widely among replicates, crops, and sampling dates. Wet‐sieving using initially moist soil showed that samples with higher initial soil water content had greater aggregate stability. Wet‐sieving performed on initially air‐dry soil samples was used for subsequent interpretation because the water content variable was removed. The presence of any crop and its roots in the planted soils versus the fallow controls was associated with increases in aggregate stability. No differences in aggregate stability were found among the different crops or over the established range of root length densities. Aggregate stability decreased from the original level during the first 14 to 21 days of the experiment, possibly due to daily watering. After 21 days, as root growth continued to increase, restabilization occurred until the original aggregate stability of the soil was exceeded for all crops. The observed increase in aggregate stability may be due in part to the physical entanglement of aggregates by roots and to the increased production of root exudates resulting from increased root growth.