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Soil compaction has increased during recent years due to the traffic with increasingly heavier machinery. We evaluated the effect of soil compaction on soil penetration resistance, rooting depth, light interception, radiation-use efficiency (RUE) and yield of three different cultivars of winter wheat (Triticum aestivum L.). On loamy sand two compaction treatments (PAC-1 and PAC-2) and a no compaction reference treatment (REF) were applied. PAC-1 was intended to affect primarily the subsoil whereas PAC-2 was intended to affect primarily the topsoil. PAC-2 showed the highest and REF the lowest penetration resistance in the topsoil, respectively. In the subsoil both compaction treatments showed higher penetration resistances than REF. In comparison with REF, the compaction treatments decreased the estimated effective rooting depth by ca. 10, 20 and 50 cm in the three winter wheat cultivars tested, equivalent to decreases in the available soil water in the root zone of up to ca. 90 mm. These differences indicate some genetic variation in the ability of cultivars to penetrate compacted soil, although the interaction between compaction treatment and cultivar was not significant. Due to almost sufficient precipitation, the impairment of root penetration resulted in a minor yield decrease of ca. 9% of grain yield in PAC-2 and ca. 8% of total dry matter (DM) in both compaction treatments. The latter was attributed to decreases in interception of light and to efficiency of light energy conversion into biomass. The RUE was positively correlated with an estimated effective rooting depth across cultivars, while DM yield was not. This correlation probably was a result of restrictions on stomatal opening mediated by drought stress and abscisic acid produced in the root system in response to occasional soil drying. Root-sourced signals, triggered in a direct response to soil compaction, may have contributed. Soil compaction has increased during recent years due to the traffic with increasingly heavier machinery. We evaluated the effect of soil compaction on soil penetration resistance, rooting depth, light interception, radiation-use efficiency (RUE) and yield of three different cultivars of winter wheat (Triticum aestivum L.). On loamy sand two compaction treatments (PAC-1 and PAC-2) and a no compaction reference treatment (REF) were applied. PAC-1 was intended to affect primarily the subsoil whereas PAC-2 was intended to affect primarily the topsoil. PAC-2 showed the highest and REF the lowest penetration resistance in the topsoil, respectively. In the subsoil both compaction treatments showed higher penetration resistances than REF. In comparison with REF, the compaction treatments decreased the estimated effective rooting depth by ca. 10, 20 and 50 cm in the three winter wheat cultivars tested, equivalent to decreases in the available soil water in the root zone of up to ca. 90 mm. These differences indicate some genetic variation in the ability of cultivars to penetrate compacted soil, although the interaction between compaction treatment and cultivar was not significant. Due to almost sufficient precipitation, the impairment of root penetration resulted in a minor yield decrease of ca. 9% of grain yield in PAC-2 and ca. 8% of total dry matter (DM) in both compaction treatments. The latter was attributed to decreases in interception of light and to efficiency of light energy conversion into biomass. The RUE was positively correlated with an estimated effective rooting depth across cultivars, while DM yield was not. This correlation probably was a result of restrictions on stomatal opening mediated by drought stress and abscisic acid produced in the root system in response to occasional soil drying. Root-sourced signals, triggered in a direct response to soil compaction, may have contributed.

The concentrations of the more‐or‐less strongly retained trace elements present in the root zone of some northern Nigerian soils were determined. The soils were chosen to represent some of the more extensively distributed soil orders under cultivation in the Nigerian savanna zone. Extraction by concentrated HNO3 was used to determine the so‐called “total”; amount of retained Cu, Zn, Pb, Ni, Cd, and B in the soils. Aqueous solutions of the chelating agents, EDTA and DTPA, were used to extract the more weakly retained Cu, Zn, Pb, Ni, and Cd; whereas, hot water was used to extract the weakly retained B. The “total”; and the more‐weakly‐retained contents of these trace elements were significantly correlated with the amount of clay, silt, and the oxalate‐extractable oxyhydroxides present in the soils; whereas, only the weakly retained elements were significantly correlated with the content of organic matter in the soil. Both the “total”; concentrations and weakly‐retained Cu, Zn, and B were so low tha...