During the seasons 2003/04, 2004/05 and 2005/06, a study was made of the evolution of runoff as well as soil and available P and K losses in the sediment carried away in a conventional till system-that most used at the present time-and in a no till system with added pruning remains in an olive grove of the picual variety located in Torredonjimeno (Jaén, Spain). A group of microplots for sediment collection in a randomized complete block design was established. The samples were collected in the field after each storm. In the study period, a total of 21 storms were recorded, with a precipitation of 450 mm in 2003/04, 179 mm in 2004/05 and 388 mm in 2005/06. The erosivity of the rainfall was characterized and the cover percentage in the plots throughout the time was determined. The establishment of pruning remains reduced soil loss with respect to conventional tillage (CT) in the 3 years (72%). Likewise, the available P loss greatly declined in the study (46.4%) under conservation agriculture. The reduction in available K loss (72.4%) was much greater than that of available P. The close relationship between both variables and sediment production also stands out. Runoff was the parameter on which the pruning remains had the least influence with only an 11% average reduction.

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Mediterranean olive trees traditionally grow under rainfed conditions, on poor soils with steep slopes. Rainfall is mainly concentrated during autumn and winter and is characterized by intense rain pulses, separated by dry periods. The use of electromagnetic induction (EMI) techniques in these olive orchards might be questioned since EMI surveys are generally recommended to be performed under moist soil conditions. A 6.7 ha olive orchard was surveyed for EMI-based apparent electrical conductivity (ECa), both under wet and dry soil conditions. In addition, 48 soil samples were analyzed for soil texture and for soil water content (SWC) under both soil conditions. The relationships between ECa, soil texture and SWC, under both soil conditions were evaluated. Despite the significantly larger ECa values measured during the wet survey as compared to the dry survey, a similar spatial correlation structure was found, indicating temporally stable ECa patterns. Significant correlations (r) were found between both surveys for ECa (r = 0.67) and for SWC (r = 0.63). The correlation between SWC and clay content exceeded 0.60 for both surveys, and the correlation between ECa and clay content was twice as high under wet soil conditions as compared to dry soil. In both situations, the ECa surveys revealed the same patterns of soil texture, indicating that moist soil conditions are not an absolute prerequisite for the use of EMI to map the spatial variability of these soil properties. Nonetheless, measuring the ECa under different moisture conditions can provide additional information about soil moisture dynamics

Core Ideas Water retention data from saturation to oven dryness were collected for a Vertisol. New water retention and differential water capacity models were developed. Draining of intra‐aggregate pore space triggers the dry field soil moisture state. Mode of the textural pore space controls shift to wet field soil moisture state. Vertisols are well suited for rainfed agriculture in water‐limited environments as a result of their unique water transfer and retention characteristics. Despite their importance, the agro‐hydrological behavior of these soils under seasonally dry climates is not yet fully understood. We collected water retention data for a Vertisol, measured from saturation to oven dryness on 27 undisturbed topsoil (0–0.05 m) samples from an experimental field in south‐central Spain and related this information to the occurrence of field‐observed preferential soil moisture states. A continuous function was fitted to the mean gravimetric water retention data, Θ, consisting of the sum of a double exponential model and the Groenevelt and Grant model. An inflection point at pressure head |h| = 1.1 × 105 cm, Θ = 0.12 kg kg−1, and an equivalent pore radius, δ = 14 nm, was interpreted as the boundary between the clay inter‐ and intra‐aggregate pore spaces, corresponding with the transition from the intermediate to the dry field soil moisture state. The mode of the textural pore space (|h| = 7.3 × 103 cm, Θ = 0.21 kg kg−1, and δ = 200 nm) matched the transition from the wet to the intermediate field soil moisture state. We related these characteristics of the soil water retention curve with the spatiotemporal soil moisture dynamics and patterns observed in the field, characterized by fast transitions between preferential soil moisture states. The proposed framework is suitable for comparing the effects of different soil management strategies on the agro‐hydrological performance of Vertisols.

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Plant cover modifies the physicochemical properties of the soil surface, which results in an enrichment in organic matter and a greater infiltration. So, this study was conducted to determine if its establishment in olive groves was effective, compared to conventional tillage, for the reduction in pollution by soluble phosphorus (P). Surface runoff, soluble P and Olsen P losses in sediment were analyzed in three experiment fields of ecological olive trees in the province of Córdoba (Spain), from 1 June 2003 to 1 June 2005. The cover system reduced the total losses of both variables in the three plots (between 7.6% and 36.5% the dissolved P loss and between 16.3% and 56.4% that of the runoff), with a certain parallelism being observed in the time distribution of the losses in both soil management systems, with significant Spearman coefficients of correlation, ranging between 0.60 and 0.98. Over half the losses of the runoff and dissolved P were produced in two or three events for the two management systems. The establishment of plant cover altered the relative composition in the Olsen P loss (raising the proportion of soluble P) and usually increased the dissolved P rate. Finally, and although it is a positive technique and highly recommendable in the area's olive groves, it was not completely effective in controlling water pollution in relation to the soluble P concentration, since this was over 0.11 mg l −1 in all the cases with a cover.

Understanding differences in the agro‐hydrologic performance of Vertisols under conventional tillage (CT) and direct drill (DD) requires a thorough knowledge of the soil hydraulic properties. We measured water retention on 54 undisturbed topsoil (0–0.05 m) samples collected at the CT and DD plots from a long‐term experiment. Water retention was significantly larger in DD (p < .05) for absolute pressure heads (|h|) ranging from 63 to 3.2 × 103 cm, and at 1.8 × 104 and 3.3 × 104 cm. A comparison of the equivalent pore‐size distributions showed combined effects of tillage in the CT topsoil and compaction as a result of machinery traffic and natural consolidation in the DD topsoil, increasing and decreasing the amount of the largest pores in CT and DD, respectively, in favour of a larger abundance of smaller equivalent pore‐sizes in DD than in CT. Significant differences in water retention and abundance of equivalent pore sizes near the dry end of the soil water retention curve (|h| ≈ 4 × 104 cm) appear to be associated with the larger organic matter content in DD. These results were corroborated by field‐measured soil water content data (0–0.10 and 0.25–0.35 m), showing a persistently larger soil water content in DD than the spatial average of both tillage systems. Differences in the observed trimodal soil water content probability density functions between CT and DD were related to equivalent pore‐sizes for which significantly different water retentions were measured. This work elucidates direct and indirect effects of soil management on water retention and the equivalent pore‐size distribution, with important consequences for the soil´s agro‐hydrologic performance. Highlights Water retention, pore‐size distribution and field soil water states of a vertisol under conventional tillage and direct drill are compared Direct drill yields larger water retention for 63 < |h| < 3.2 × 103 cm, and at |h| = 1.8 × 104 and 3.3 × 104 cm. Larger water retention near |h| ≈ 4 × 104 cm in direct drill is associated with larger organic matter content Field soil water states are controlled by specific SWRC and pore‐size distribution ranges in both management systems