Subsoil compaction effects on crops in Punjab, Pakistan: I. Soil physical properties and crop yield

Traffic on agricultural land, inappropriate tillage, and poor timing of field operations cause subsoil compaction, which decreases soil productivity and crop yields. A field experiment was conducted during 1997–1998 and 1998–1999 on a sandy clay loam (fine-loamy, mixed, hyperthermic Typic Haplargids, USDA; Luvic Yermosol, FAO) to study subsoil compaction effects on soil physical properties, and yield of wheat ( Triticum aestivum L.) and sorghum ( Sorghum bicolor L. Moench). Soil compaction was artificially created once at the start of the study. The 0.15 m top soil layer was manually removed with a spade. The exposed layer was compacted with a mechanical compactor to a bulk density of 1.93 Mg m −3. The topsoil was then again replaced above the compacted subsoil and levelled. Both compacted and control plots were hoed manually and levelled. This soil compaction treatment resulted in a 38% decrease in grain yield of wheat during 1997–1998 and 8% during 1998–1999. In contrast, straw yield decreased by up to 12% in 1997–1998 and was not affected in 1998–1999. The number of fertile tillers was significantly lower during 1997–1998 in the compacted treatment than in control. However, plant height and 1000-grain weight were unaffected by compaction. In accord with bulk density, penetration resistance increased and total porosity and air-filled porosity decreased significantly due to subsoil compaction. Subsoil compaction reduced both the water and nutrient use efficiencies of wheat by about 38% in the first year and 9% in the second year. Soil compaction also reduced fodder yield, and water and nutrient use efficiencies of sorghum by 22% in 1998 and 14% in 1999. After three crops, soil bulk density and penetration resistance decreased in the compacted zone, indicating the ameliorating effect of cropping on soil physical properties. The subsoil compaction effects on soil properties and yield, however, persisted for 2 years. Results showed that subsoil compaction adversely affected soil physical properties, which decreased yields as well as water and nutrient use efficiencies by crops. Therefore, appropriate measures such as periodic deep ploughing, controlled traffic, conservation tillage, and incorporating of crops with deep tap root system in rotation cycle is necessary to minimize the risks of subsoil compaction.