Crop responses to applied soil compaction and to compaction repair treatments

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Crop responses to annual compaction treatments (applied to whole plots) and management treatments to ameliorate compacted soil were determined in a field experiment on a Vertisol. Initially, all treatments except a control were compacted with a 10 Mg axle load on wet soil (26% gravimetric water content compared with a plastic limit of 22%). Annually applied axle loads of 10 and 6 Mg on wet soil (25–32% soil water) tended to reduce seedling emergence, grain yield (wheat, sorghum and maize), soil water storage and crop water use efficiency (WUE). Annual applications of an axle load of 6 Mg on dry soil (<22% soil water) had little effect on crop performance. Mean reductions in the yield of five crops (three wheat, one sorghum and one maize) in comparison with the uncompacted control were 23% or 0.79 Mg ha −1 (10 Mg on wet soil), 13% or 0.44 Mg ha −1 (6 Mg on wet soil) and 1% or 0.03 Mg ha −1 (6 Mg on dry soil). Maize grown in the fifth year of treatment application was most affected by compaction of wet soil, its WUE being reduced from 14.3 to 9.7 kg ha −1 mm −1 in response to an axle load of 10 Mg. Reduced WUE was associated with delayed soil water extraction at depth. A 3-year pasture ley was the most successful amelioration treatment. A wheat and a maize crop grown after the ley outyielded the control by 0.33 and 0.90 Mg ha −1, respectively. So the pasture not only ameliorated the initial compaction damage, with respect to crop performance, but resulted in improvements in two subsequent crops.