J.L. Arrúe

Drip irrigation, soil characteristics and the root distribution and root activity of olive trees

A study was carried out on the root distribution and root activity of the olive tree (Olea Europaea, L., var. manzanillo) as influenced by drip irrigation and by several soil characteristics such as texture and depth. The experiments were conducted in two plots within a drip-irrigated grove of 20-year-old trees planted at 7×7 m spacing. One soil was a sandy loam, the other a clay-loam. Both cylinder and trench methods were used to determine root distribution. Labelling with 32P was used to determine root activity. Under dryland conditions the adult tree adapted its rooting system, following the installation of a drip system, by concentrating the roots within the wet soil zones near the drippers. The highest root densities occur in those zones, down to a 0.6 m depth, the most abundant being the <0.5 mm diameter roots. The most intensive root activity was also found in that zone. For a given irrigation system, wet soil bulbs are more extensive and therefore root distribution expands to a larger soil volume when the soil is more clayey and with a hard calcareous pan present at about 0.8 m depth which prevents deep drainage.

Growth, yield and water use efficiency of winter barley in response to conservation tillage in a semi-arid region of Spain

In the semi-arid areas of Aragon (NE Spain), dryland crop production is limited by low and variable precipitation. Conservation tillage has been proposed as a promising strategy to improve soil and water conservation in these areas. A long-term field research project to determine the feasibility of conservation tillage was initiated in 1989 at four locations, three on loam to silt loam soils (Xerollic Calciorthid) and one on a silty clay loam (Fluventic Ustochrept), receiving between 300 and 600 mm of average annual rainfall. This study compared, under both continuous cropping and cereal-fallow rotation, the effects of conventional tillage (mouldboard plough) and two conservation tillage systems, reduced tillage (chisel plough) and no-tillage, on winter barley (Hordeum vulgare L.) growth and yield, and water use efficiency during the first two growing seasons. Whereas a similar crop response between the conventional and reduced tillage treatments was generally found at all locations, poor performance with no-tillage was observed at the most arid sites. At these sites, lower early growth of barley with no-tillage resulted in a 53% reduction in grain yield, compared to conventional tillage. This unfavourable crop response to no-tillage was due to a lower crop water use, mainly starting with the stem elongation stage (20% lower than the tilled treatments), and a larger proportion of total water use lost as evaporation (69% compared to 50% of tilled treatments). Values of water use efficiency for grain production (0.7–17.0 kg ha−1 mm−1) and transpiration efficiency (7.4–23.8 kg ha−1 mm−1) were within the ranges reported for cereal crops in Mediterranean environments. Fallowing in the cereal-fallow rotation proved to be an inefficient practice for improving soil water storage and subsequent crop yield, under both conventional and conservation management. Based on the study, we conclude that, up to now, only reduced tillage provides an alternative to conventional tillage to maintain crop production in the dryland cereal-growing areas of Aragon.

A comparison between seasonal changes in soil water storage and penetration resistance under conventional and conservation tillage systems in Aragón

Abstract Low and extremely variable precipitations limit dryland crop production in the semi-arid areas of Aragon (NE Spain). These areas are also affected by high annual rates of topsoil losses by both wind and water erosion. A long-term experiment to determine the feasibility of conservation tillage in the main winter barley production areas of Aragon was initiated in 1989 at four locations, three on loam to silt loam soils (Xerollic Calciorthid) and one on a silty clay loam (Fluventic Ustochrept), receiving between 300 and 600 mm of average annual rainfall. In this study, we compared, under both continuous cropping and cereal-fallow rotation, the effects of conventional tillage (mouldboard plough) and two conservation tillage systems, reduced tillage (chisel plough) and no-tillage, on soil water content and penetration resistance during the first two growing seasons. Whereas reduced and conventionally tilled treatments generally had similar soil water content during the experimental period, the effects of no-tillage were inconsistent. No-tilled plots had from 26% less to 17% more stored soil water (0–80 cm) than conventional tilled plots at the beginning of the growing season. In contrast to the conventional and reduced tillage treatments, penetration resistances were between 2 and 4 MPa after sowing in most of the plough layer (0–40 cm) under no-tillage at all sites. Fallow efficiencies in moisture storage in the cereal-fallow rotation, when compared with the continuous cropping system, ranged from −8.7 to 12%. The highest efficiencies were recorded when the rainfall in the months close to primary tillage exceeded 100 mm. Since this event is very unlikely, long fallowing (9–10 months) appears to be an inefficient practice for water conservation under both conventional and conservation management. Our results suggest that, up to now, only reduced tillage could replace conventional tillage without adverse effects on soil water content and penetration resistance in the dryland cereal-growing areas of Aragon.

Tillage effects on soil surface conditions and dust emission by wind erosion in semiarid Aragón (NE Spain)

Wind erosion is one of the most serious soil degradation problems in many agricultural regions of the world. Due to particular soil and climate conditions and inappropriate agricultural practices, Central Aragon (NE Spain) is a semiarid region prone to land degradation by wind erosion. However, actual wind erosion data are not yet available. We report here results from a wind erosion study conducted during the summer 1995 within a single dryland field located in Central Aragon. Two consecutive field experiments investigated the effects of chisel ploughing (reduced tillage) and mouldboard ploughing (conventional tillage) on soil surface conditions and vertical dust flux. Micrometeorological data and suspended sediment samples were collected in the month following each tillage operation. Likewise, soil surface properties affecting wind erosion were determined immediately after tillage. Values of vertical dust flux varied from 0.52 to 5.03 μg m−2 s−1 (for a range of wind shear velocity of 0.46–0.56 m s−1) during the first experimental period (after chisel ploughing) and from 1.45 to 11.66 μg m−2 s−1 (for shear velocities between 0.37 and 0.72 m s−1) in the second experiment (mouldboard ploughing). The wind-erodible fraction of soil surface (aggregates<0.84 mm diameter) was 41% and 50% after chiseling and mouldboard ploughing, respectively. The percentage of soil cover with crop residues and clods was 15% after chiseling and only 4% after mouldboard ploughing. The frontal area of this nonerodible material and soil roughness was reduced four times after mouldboard ploughing. Although direct comparisons of tillage effects are still necessary, these first results suggest that reduced tillage, with chiseling as primary tillage, could be considered as a viable alternative for wind erosion control during the fallow period in semiarid Aragon. This study indicates, likewise, the need to consider the temporal and spatial variability of soil properties affecting wind erosion in agricultural soils.

Effects of reduced tillage on soil surface properties affecting wind erosion in semiarid fallow lands of Central Aragon

Abstract In Central Aragon (NE Spain), where strong and dry winds are frequent all year round, fallow lands are susceptible to wind erosion due to insufficient crop residues on the surface and loose, finely divided soils by multiple tillage operations. Effects of conventional tillage (CT — mouldboard ploughing followed by a compacting roller) and reduced tillage (RT — chisel ploughing) on soil surface properties affecting wind erosion were studied during three experimental campaigns in a dryland field of Central Aragon. RT provided higher soil protection than CT through a lower wind erodible fraction of soil surface (on average, 10% less) and a significantly higher percentage of soil cover with crop residues and clods (30% higher). Random roughness was also higher after RT than after CT (15 vs. 4%). These results indicate that RT can be an effective soil management practice for wind erosion prevention during the fallow period in semiarid Aragon. The study shows, likewise, that significant changes in soil aggregate size distribution associated with wind erosion processes may occur in short periods of time. Thus, temporal variability of soil surface properties, including crust and clods stability, needs to be considered in wind erosion research in agricultural soils.