Soil structural changes caused by agricultural machinery

Authors: Guber, Andrey; Pachepsky, Yakov

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 10/23/2007
Publication Date: 11/19/2007
Citation: Guber, A.K., Pachepsky, Y.A. 2007. Soil structural changes caused by agricultural machinery. In: Proceedings of the IX Internationl Symposium and IV National Congress of Sustainable Agriculture, November 19-21, 2007, Port Veracruz, Mexico. p.43-55.

Interpretive Summary: Soil structure greatly influences soil physical status, soil quality, and soil fertility including the sustainable support of agricultural production. Soil structure is affected by soil management practices. Soil compaction has various unfavorable consequences, therefore diagnosis, forecasting, and mitigation of soil compaction presents an important challenge for soil scientists and agronomists. The objective of this work was to evaluate the sensitivity of parameters of soil fragmentation into aggregates and changes in soil structure caused by compaction due to heavy tractor passes. The increase in the number of tractor passes increased the depth to which soil structure was affected and changed values of soil porosity. Soil structure worsened more when soil was wet. The relationship between mass and size of dry aggregates was more sensitive to compaction than the bulk structure measures such as aggregate size distribution and bulk density. The change in mass-size relationship of dry aggregates combined with the swelling rate of dry aggregates shows definite promise as a means for early diagnosis of soil compaction.

Technical Abstract: Effects of tractor traffic with high axle load on the aggregate size distribution, the total soil porosity, and the aggregate porosity were studied in a field experiment on a silty clay loam Greyzem soil. One and three tractors passes were made at pre-irrigated and non-irrigated 10x10 m plots. The value of mass fractal dimension was derived from density-size relationships in air-dry aggregates. Tractor passes compacted soil at both plots to the depth of 40 cm. At the pre-irrigated plot, one and three tractor passes increased the percentage of the largest aggregate fraction '7 to 10 cm' in 0-5 cm and 0-15 cm soil layers, respectively. On the contrary, at the non-irrigated plot, compaction did not affect the aggregate size distribution. The increase in the number of passes caused the progressive compaction resulting in decrease of the total soil porosity to the depth of 40 cm. The porosity decrease was more pronounced in the 0-15 cm layer at the pre-irrigated plot. Dependencies of the specific pore volume of aggregates on the gravimetric water content (aggregate swelling) and the aggregate mass-size scaling showed that the compaction altered the aggregate porosity. This implies that these characteristics show promise for soil compaction diagnostics.