Subsoil compaction effects on crops in Punjab, Pakistan: II. Root growth and nutrient uptake of wheat and sorghum

Crop yields can be reduced by soil compaction due to increased resistance t o root growth, and decrease in water and nutrient use efficiencies. A field experiment was conducted during 1997-1998 and 1998-1999 on a sandy clay lo am (fine-loamy, mixed, hyperthermic Typic Haplargids, USDA; Luvic Yermosol, FAG) to study subsoil compaction effects on root growth, nutrient uptake a nd chemical composition of wheat (Triticum,l aestivum L.) and sorghum (Sorg hum bicolor L. Moench). Soil compaction was artificially created once at th e start of the study. The 0.00-0.15 m soil was manually removed with a spad e. The exposed layer was compacted with a mechanical compactor from 1.65 Mg m(-3) (control plot) to a bulk density of 1.93 Mg m(-3) (compacted plot). The topsoil was then again replaced above the compacted subsoil and levelle d. Both compacted anti control plots were heed manually and levelled. Root length density, measured at flowering stage, decreased markedly with compac tion during 1997-1998 but there was little effect during 1998-1999. The red uction in nutrient uptake by wheat due to compaction of the subsoil was 12- 35% for N, 17-27% for P and up to 24% for K. The reduction in nutrient upta ke in sorghum due to subsoil compaction was 23% for N, 16% for P, and 12% f or K. Subsoil compaction increased N content in wheat grains in 1997-1998, but there was no effect on P and K contents of grains and N and P content o f wheat straw or sorghum stover During 1997-1998, K content of wheat straw was statistically higher in control treatment compared with compacted treat ment. In 1998, P-content of sorghum leaves was higher in compacted treatmen t than uncompacted control. Root length density of wheat below 0.15 m depth was significantly reduced and was significantly and negatively correlated with soil bulk density. Therefore, appropriate measures such as periodic ch iselling, controlled traffic, conservation tillage, and incorporating of cr ops with deep tap root system in rotation cycle is necessary to minimize th e risks of subsoil compaction. (C) 2001 Elsevier Science B.V. All rights re served.