Soil compactibility as affected by soil moisture content and farmyard manure in central Iran

Soil compactibility which basically depends on soil texture, organic matter and soil water content during farm machinery traf®cking are major factors affecting soil conservation. In a ®eld experiment, cattle farmyard manure was applied to a silty clay loam soil (®ne-loamy, mixed, thermic Typic Haplargids, USDA; Calcaric Cambisols, FAO) in Isfahan, Iran. Three rates, 0, 50, 100 Mg haÿ1 (on oven dry basis) of farmyard manure, were incorporated into the topsoil. After 5 months, a two-wheel drive tractor (48.5 kW) was passed over the plots once (P1) or twice (P2) at soil moisture contents associated with the plastic limit (PL), 0.8PL, and 0.6PL. A randomized complete block design with four replicates with treatments nested (split-block) into the blocks was used. Bulk density (BD), cone index (CI) and soil sinkage were measured as indices of soil compactibility and traf®cability. Applying 50 and 100 Mg haÿ1 of manure signi®cantly counteracted the effects of load and wetness on BD and CI. There was a signi®cant difference between the effects of 50 and 100 Mg haÿ1 of manure on BD, but not on CI. Manure application also reduced the subsoil compaction. Double passes of the tractor (P2) signi®cantly increased compaction. There was a limitation for traf®cability for no-manure treatment even at 0.6PL, whereas this limit was reached at 0.8PL for the 50 Mg haÿ1 treatment. Results from this study demonstrate that manure application at a rate of 50 Mg haÿ1 reduced soil compactibility and increased soil moisture traf®cability range. Thus, increasing soil organic matter could bring about an appropriate solution for sustainable soil management in the region. # 2000 Elsevier Science B.V. All rights reserved.