Influence of a compacted loam subsoil layer on growth and yield of irrigated cotton in Southern Spain

Subsoil compaction, which may occur naturally or be a consequence of machinery traffic, causes reductions in crop yields. The aim of this work was to characterize the effects of subsoil compaction on growth and yield of cotton (Gossypium hirsutum L.) under held conditions, Two field experiments were carried out in Cordoba, Spain, on an Eutric Fluvisol With loam texture. A treatment with a compacted layer (bulk density of 1.6-1.7 Mg m(-3)) at 0.2-0.4 m depth was compared with a control treatment with maximum bulk density of about 1.4 Mg m(-3). Soil resistance to penetration was related to soil bulk density and water content. The compaction provoked reductions in root length (40% in 1996 and 33% in 1997), leaf area index (26% in 1996 and 12% in 1997), evapotranspiration (12% in 1996 and 7% in 1997) and seed cotton yield (28% in 1996 and 10% in 1997). Average resistance to penetration in the compacted layer was above 3 MPa (a threshold for cotton root growth according to the literature) but root growth was observed below this layer. It was speculated that spatial variation of soil bulk density and resistance and temporal variation of soil water content allowed the roots to find weaker path-ways to cross the compacted layer. The effect of the subsoil compaction on the soil characteristics and the root growth remained during the second experimental year but it was less pronounced on the above ground plant growth, development and yield. It was concluded that subsoil compaction influences significantly growth and yield of cotton, but successive cropping may alleviate the effects of the compaction. (C) 2000 Elsevier Science B.V. All rights reserved.