Soil physical properties, water depletion and crop development under traditional and conservation tillage in southern Spain

Tillage methods affect soil physical properties and, thus, have a direct influence on the replenishment and depletion of soil water storage and crop performance. This study was conducted to determine the effects of traditional and conservation tillage on soil physical properties, soil water replenishment and depletion, and crop development and yield under southern Spanish conditions. The experiments were carried out from 1992 to 1995 in a sandy clay loam soil (Xerofluvent). The traditional tillage (TT) method consisted mainly of the use of mouldboard ploughing, and the conservation tillage (CT) was characterized by not using mouldboard ploughing, by reduction of the number of tillage operations and leaving the crop residues on the surface as mulch. In both tillage treatments a wheat (Triticum aestivum, L.)-sunflower (Helianthus annuus, L.) crop rotation was established. In each treatment, systematic measurements of bulk density, resistance to penetration, infiltration rate and hydraulic conductivity (using tension disc infiltrometers) in the soil top layer were carried out. Changes in water profiles through the experimental period were also followed using a neutron probe. Crop development and yield were determined. The soil hulk density in the 0 to 20 cm layer was significantly higher in the CT than in the TT treatment, mainly after tillage operations (between 10% and 24% higher in CT than in TT). After 3 years of continuous tillage treatments, the soil bulk density did not increase. The resistance to penetration at any time was higher in the CT than in the TT treatment, but not always significantly different. Infiltration rates were significantly higher in the TT than in the CT treatment (about 35% higher in TT than in CT). After 3 years of the tillage treatments the hydraulic conductivity of the soil surface layer, at a pressure head of 0 mm, was significantly higher in the CT (124 mm h-1) than in the TT (66 mm h-1). This is related to the existence of preferential paths created by an increase of the earthworm population in the CT treatment. Soil water profiles showed higher replenishment of soil water storage in the CT than in the TT treatment, particularly from October 1994 to June 1995 when the lowest precipitation of the experimental period was recorded. Plant height, leaf area index (LAI) and root length density (RLD) of the first sunflower crop were significantly higher in the TT than in the CT treatment. Nevertheless, the seed yield was slightly higher in the CT than in the TT treatment. In the second sunflower crop, plant height, LAI, RLD were significantly higher in the CT than in the TT treatment except early in the season, and yield was significantly (and extremely) higher in the CT (1521 kg ha-1) than in the TT (473 kg ha-1) treatment. During the wheat crop season, plant height and RLD were higher in the TT than in the CT treatment, but groin yield was again slightly higher in the CT than in the TT treatment. The conservation tillage applied seems to be highly effective in enhancing soil water recharge and water conservation, particularly in years with much lower than average precipitation.

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