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EFFECT OF REDUCTION OF SOIL COMPACTION THROUGH ORGANIC MATTER INCORPORATION ON CROP YIELD

J.O. OHU, G.S.V. RAGHAVAN and E. McKYES

McGill University, Macdonald College, Department of Agricultural Engineering, 21 111Lakeshore Road, Ste. Anne de Bellevue, P.Q. H9X ICO (Canada)

It has been known for a long time that excessive soil compaction can reduce crop yields. Among the available means of reducing this effect is the alteration of the soil composition to reduce mechanical strength of compacted soils. Although relatively high yields in highly compacted soils are often attributed to high organic matter content, the quantitative effect of adding organic matter to soils as a means of soil compaction reduction has been given little attention. To study this process, peatmoss was added to three soil textures to provide 3-, i0- and 17-% (w/w) organic matter levels for each soil. The soils were compacted in the laboratory using 5, 15 and 25 blows of a standard Proctor compaction hammer. The physical properties of the soils were measured and the interaction of the compaction and organic matter effects on the production of bush bean (Phaseolus vulgaris) was studied in a controlled environment. Test results showed a decrease in bulk density and penetration rsistance, along with improved water availability and hydraulic conductivity, due to increases in organic matter content of the compacted soils. Bush bean yields were better at both 10- and 17-% (w/w) organic matter levels than at the 3-% (w/w) organic matter level, irrespective of the compaction energy applied to the soils. However, the benefits due to organic matter incorporation were more noticeable with an increase in organic matter from 3 to 10% (w/w) than from i0 to 17% (w/w). Therefore, before general practical recommendations can be made, more work will be needed to determine the level of organic matter that best suits different soll textures for the production of different crops. From all the observations and analyses, it is evident that there is a great potential for using organic matter to alleviate the problem of soil compaction in soll management practices for crop production.

A MODEL TO PREDICT SOIL COMPACTION DUE TO FIELD TRAFFIC

A.L.M. VAN WIJK and J.J.H. VAN DE AKKER

Institute for Land and Water Management Research (ICW), P.O. Box 35, 6700 AAWagenlngen (The Netherlands)

In the Netherlands, during the last 10-15 years, soil compaction has tended to occur over an increasing area and to a greater depth in the soil. In the same period, crop rotation was intensified by replacing cereals by root crops and silage maize. At present, more than 60% of the arable land is used for growing potatoes (2~%), sugar beet (18%) and silage maize (22%). These crops produce 50-60 t ha-- of fresh bulk mass, which has to be harvested in autumn under predominantly wet soil conditions. This development was attended by continuing mechanization with increasing wheel loads. Since a couple of years, the consequences of these developments for physical soil conditions as well as crop growth are studied in the field. In addition to these field studies there is a need for tools that enable the study of soll compaction under a wide variety of traffic patterns and soll conditions. A soil compaction simulation model may be such an expedient. A first version of a soil compaction model and some results are presented. The model is based on the