Concentrated flow erosion in Mediterranean cultivated areas is considered a major process of land degradation. Rills and ephemeral gullies in a 6.4 ha olive orchard catchment located in an intensive ...commercial farm, which could represent a common degradation scenario in hilly areas, were measured and compared with the sediment loads at the outlet. Four GPS survey campaigns were carried out between March 2009 and March 2014, for periods with cumulative precipitation ranging between 728 and 121 mm. Chopped pruning residues were kept on the lanes during campaigns 2–4, whereas a grass cover crop was seeded in campaign 4. Rainfall, runoff and sediment loads were measured in a flume gauge station at the catchment outlet.
The ratio of concentrated flow erosion to catchment sediment load varied between 1.0 and 35.0. Total concentrated flow erosion ranged between 25.0 and 0.1 t ha−1. Rill erosion was the dominant process on ephemeral gullies for three campaigns, with a mean contribution to the total concentrated flow erosion of 55%. Rills clearly followed tractor tracks along the most parallel lanes to the maximum slope. Therefore, a change in traffic direction would be helpful to reduce the connectivity, controlled by the spatial distribution of rows and lanes in the farm. Olive plantation distributions should prioritize hydrological criteria to adapt traffic patterns in olive farms, as long as the tractor manoeuvrability and risk of overturning are not adversely affected.
Although the farmer only kept the cover crop for one campaign, it proved to be an efficient measure for interrupting rills along the lanes, whereas pruning residues were effective for the control of interrill erosion. On‐site application of pruning residues reduced their handling and transport costs, while increasing the soil fertility and soil cover. However, guidelines for the efficient application of pruning residues are still necessary in terms of residue rates and orientation.
Rills and ephemeral gullies were compared with sediment loads at the catchment outlet for four campaigns with different conservation measures. The ratio of concentrated flow erosion to total sediment load varied between 1.0 and 35.0. The average contribution of rill erosion to total concentrated flow sediments was 55%. Olive plantation distributions should prioritize hydrological criteria to adapt traffic in farms and the application of cover crops to the control of rills. Chopped pruning residues were suitable to reduce interrill erosion.
Most field erosion studies in agricultural areas provide little information on the probable errors involved. Here, for the first time, we compare the accuracy, time and cost of conventional and new ...methodologies for gully surveying, and provide a model to estimate the effort required to achieve a specified accuracy. Using a terrestrial LiDAR survey of a 7.1‐m‐long gully reach as a benchmark data set, the accuracies of different measurement methods (a new 3D photo‐reconstruction technique, total station, laser profilemeter, and pole) are assessed for estimating gully erosion at a reach scale. Based on further field measurements performed over nine gullies (>100 m long), a simulation approach is derived to model the expected volume errors when 2D methods are used at the gully scale. All gullies considered were located near Cordoba, Spain. At the reach scale, the field measurements using 3D photo‐reconstruction and total station techniques produced cross‐sectional area error values smaller than 4%, with other 2D methods exceeding 10%. For volume estimation, photo‐reconstruction proved similar to LiDAR data, but 2D methods generated large negative volume error (EV) values (<–13% for laser profilemeter and pole). We show that the proposed error expressions derived from the model are in line with the reach‐scale field results. A measurement distance factor (MDF) is defined that represents the ratio between cross‐section distance and the gully length, and thus reflects relative survey effort. We calculate the required MDF for specified values of EV, illustrating how MDF decreases with increasing gully length and sinuosity.
•We monitored soil erosion and runoff in a olive commercial farm over 6 years.•We describe interactions between soil management decisions and rainfall variability.•In 3 out of 6 years, sediment loads ...were >10tha−1year−1, despite CAP requirements.•Benefits of soil conservation measures (grass cover and mulch) could not be proven.•Economic losses associated with water erosion were not evident in the olive yield.
To measure the erosive processes taking place under conditions close to those experienced by farmers and land managers; analyses on spatial units adapted to the size of the farm must be carried out; in a non-isolated way in the case of conventional plots. The objective of this study was to describe and understand the current state – in terms of high soil losses and degradation risk – of a commercial olive farm following the CAP agro-environmental requirements as well as the interaction between soil management decisions and rainfall variability. In this work, rainfall and runoff soil loss for 6.4 hydrological years (2005–2011) were monitored in the outlet of an olive orchard microcatchment of 6.7ha. The equipment used was a flume with an ultrasonic sensor to measure flow height, a rainfall gauge and a sediment sampler. Management systems and olive yields were described for the study period. Different management operations (no-tillage, conventional tillage, no herbicides with tillage and mulch) were applied in the field as a result of the farmer adapting to yearly conditions and to recommendations on good agricultural practice.
Our results indicate that the interaction between the factors of annual climatological features and management determined the hydrology, soil loss and olive yield. On the annual scale, cumulative rainfall and rainfall erosivity varied between 600 and 1000mm and 600 and 1500MJMmha−1h−1, respectively. The average annual runoff coefficient was equal to 15±10%, while total sediment loss ranged from <1tha−1year−1 to >20tha−1year−1. Olive yield ranged between 5000kgha−1year−1 and 10,000kgha−1year−1. Above average annual rainfall values were associated with both high yields and soil losses >10tha−1year−1.
For the study period, frequent events with a low return period resulted in soil losses >10tha−1, despite the use of different soil management techniques and the compliance of CAP agro environmental regulations. The high risk of soil degradation evaluated might mean that the criterion based on slopes >10% is not suitable for the application of agro-environmental requirements of CAP. On the other hand, further research on conservation technologies such as a more efficient use of cover crops, mulches and plant barriers, controlled traffic farming and/or changes in land use is needed.
A study was undertaken into the environmental and economic impacts of different soil management strategies, spontaneous grass cover with and without gully control (SC/SCGC) or conventional tillage ...with and without gully control (T/TGC), based on the experimental results obtained in an 6.1ha olive crop microcatchment. Initially, 2years of rainfall–runoff–sediment load data series, (34 events) recorded under the current management (SCGC), was used for the calibration of the AnnAGNPS model at event and monthly scales providing suitable adjustments of runoff, peak flow and sediment loads (E>70, r>0.85).
Ephemeral gullies were also identified using aerial orthophotography and field work. The module of the AnnAGNPS model for simulating ephemeral gully generation and the tillage operations based on a bibliographical review were used to compare different scenarios and to perform a 10year-analysis. The results showed mean runoff coefficients of 10.0% for SC/SCGC and of 3.2% for T/TGC while the average sediment loads were 2.0t∗ha−1∗year−1 (SCGC), 3.5t∗ha−1∗year−1 (SC), 3.3t∗ha−1∗year−1 (TGC) and 4t∗ha−1∗year−1 (T). Significant differences in sediment sources (rill/inter-rill erosion and ephemeral gullies) were evaluated between SC (46% of gully contribution) and T (19% of gully contribution), in order to optimize the environmental and economic effort required in each case. Finally, the annual costs associated with soil losses were estimated (<1€∗ha−1∗year−1). SC was the most profitable alternative for soil management. Despite the additional reduction in soil losses of the SCGC approach, the higher cost of its implementation and the minor effect on yield losses in the medium term suggest that without additional support (such as subsidies for gully control measures), farmers would have not an obvious incentive to use it.
► We calibrated AnnAGNPS model in an olive orchard catchment. ► We model the environmental and economic impact of different soil managements. ► Significant differences in sediment losses and gully contribution were found. ► No obvious incentives to apply soil protection measures due to higher costs.
Despite the fact that the microcatchment scale allows us to evaluate the real complexity of soil protection in fields, few studies have been carried out in olive groves. This paper explores, on ...annual and event scales, the hydrological and erosive patterns observed in an olive microcatchment of about 6ha under non-tillage with spontaneous grass cover, where data series of runoff and sediment load have been measured in a contrasting hydrological period of over 5years. Firstly, the features of the data series acquired in the study station and its temporal context were explored through statistical analysis (statistics, histograms and correlation test), the intensity–duration–frequency relationships and the annual values of MOPREDAS dataset (1946–2005). In addition, annual and seasonal patterns were checked through Principal Components Analysis (PCA) to characterize the impact of rainfall variability and management techniques. Events with return periods of under 3years caused sediment loads between 7.2 and 17.0Mg., which implies that very high soil losses can be expected from frequent events. Although the contribution of a few events to the annual runoff and sediment load is substantial, a different distribution characterized by prolonged rainfall periods and very high soil losses was observed for a “rainy year” 2009–2010 (with an accumulated frequency of annual rainfall close to 79%). The PCA illustrated a seasonal pattern of events where low values of soil losses and sediment concentration were observed in spring. This is probably associated to lower soil moisture and to sediment being trapped by the grass cover. Finally, the minimal cost of the spontaneous cover for soil protection encourages its use, despite the fact that could be inefficient when inter-rill erosion is either not the main source of sediment in the catchment or it is not well-established.
•Hydrological-erosive patterns are explored in an olive grove catchment with a grass cover.•Despite the cover, high soil losses are expected from events of a larger 5-year-return period.•Although few events mostly determined annual balances, different patterns were described.•The dense cover and the low soil moisture determined low sediment discharges in spring.
Olive orchards located in mountainous or hilly landscapes in Southern Spain have been identified as one of the major sources of sediments for streams in the region. This paper presents a modeling ...study of the magnitude and spatial distribution of sources of sediment within a small 6.1
ha olive orchard forming a microcatchment in a mountainous area. The model used was SEDD, which was calibrated using rainfall, runoff and soil erosion patterns monitored over a 3-year period. Although the data series are incomplete, 46 events were observed. SEDD permitted an analysis of the erosive behavior and the sediment delivery ratio (
SDR) in the catchment on an event scale. High variability in catchment responses was observed, due to differences in the characteristics of storms and the seasonal ground cover. A small group of two or three erosive events, occurring mainly in autumn, were responsible for most annual runoff and sediment loads, while the impact of spontaneous grass cover was apparent in events occurring in spring, where, despite high runoff depth, the sediment loss was low. This bimodal tendency justified the calibration of the SEDD model through the medians of
β-values in both the periods September–January and February–June. The results of the calibration (
E
=
0.97 and
RMSE
=
0.03
t
ha
−
1
) confirmed the applicability of SEDD to predict soil loss in the microcatchment and to allow us to complete the data series. Although the annual mean of
SDR in the catchment for the study period was 3.8%, high spatial variability was found in the geomorphological units identified, with
SDR values between 0.3% and 21.7%. On the event scale, probabilities of 50% for surpassing an SDR value of 10% were calculated for only 6% of the catchment area. The location of these most significant sources of sediment will permit the design of more efficient management plans in order to reduce sediment discharge into streams.
► We apply SEDD model to explain erosion spatial pattern in an olive tree catchment. ► We explore the impact of the model factors C-USLE, erosivity and β -parameter. ► We identified a bimodal β-distribution allowing to obtain a fine calibration. ► Rainfall seasonal pattern and cover protection justified the model adjusting. ► Empirical studies should explore the heavy deposition calculated in the catchment.
Water balance models on the monthly scale are commonly used for planning purposes due to the relative simplicity of their parameterization and because monthly data are more readily available than ...daily data. The aim of this study was to evaluate the performance of three hydrological models, suitable as hydrological planning tools in rural engineering projects: one multiple linear regression (MLR) and two water balance models (one with daily and the other with a monthly time step, named DWBR and SIMPA, respectively). Runoff in both models are based on the Curve Number approach. The evaluation was conducted on a large olive orchard catchment of 308 km
2
using a daily rainfall-runoff dataset of 9 years.
SIMPA and DWBR performed better than the MLR model. The SIMPA results were heavily dependent on the parameter soil water storage capacity, as determined from Monte Carlo analysis, although they showed the best adjustments (with a mean Nash-Sutcliffe Efficiency = 0.78 and 0.66 for calibration and validation, respectively). In addition, inconsistent parameterization could be obtained in both SIMPA and DWBR when the aquifer recharge coefficient was included in the set of parameters to be calibrated. The advantage of DWBR against SIMPA is that the daily temporal scale is more physically meaningful than the monthly scale. Extreme runoff values were responsible for most simulated-measured runoff deviations for the three models. Despite the good performance and conceptual advantages of SIMPA and DWBR, they should not be applied without previous calibration.
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•108 scenarios were built with AnnAGNPS to model SOC in an olive grove catchment.•The main variables for SOC modeling were identified with a sensitivity analysis.•Sediment OC had a ...maximum with the combination NT-Clo whereas SOC pool with C-SC-F3.•CN, soil and fertilization type were the most significant features for calibration.•Annual OC exported and SOC pool simulations were also compared with field studies.
Soil organic carbon (SOC) stock changes are crucial in identifying risk of desertification in fragile areas In this work, 108 scenarios were prepared with the model AnnAGNPS in a small catchment of extensive olive groves by considering 6 different soil types (with textures sandy, S; sandy loam, Slo; loam, L; clay loam, Clo; silty loam clay, SiLoC; clay, C), 3 different managements (no till, NT; conventional tillage, CT, and cover crop, SC), 3 types of fertilization (two organic at rates of 40 and 80 kg.ha−1, F2 and F3, and another inorganic F1 with 100 kg.ha−1), and 2 contrasting reach organic carbon half-life time (0.1 day–730 days). The consistency of simulated annual OC attached to sediment and variations in ground SOC (h = 200 mm) were evaluated and compared in the context of the region of Andalusia, Spain. In addition, the most significant parameters to consider in the subsequent calibration process were also identified.
There were significant differences in annual exported OC for the scenarios of soil and management, ranging between 0.0 kg.ha−1 and 368.9 kg.ha−1. In addition, S and SC showed the lowest variability intervals, while Clo and NT had the highest OC values and variation ranges. For the SOC pools, the effects of soil and fertilization were more evident than that of management. The combination C-SC-F3 presented the maximum increase of SOC (0.150 mg OC.g-1soil.y-1) as a result of the maximum OC inputs while Slo-NT-F1 presented the minimum (0.080 mg OC.g-1soil.y-1). Finally, the most significant parameters derived from the sensitivity analysis were soil texture, saturated hydraulic conductivity and Curve Numbers for annual exported OC and ground OC, fertilization parameters and rate of decomposition of residues. Model parameterization based on a sensitivity analysis and the abundance of previous experimental studies supports the AnnAGNPS applications for simulating the OC loss in agricultural catchments.
•A lab method for estimating soil water diffusivity was extended for field use.•Effective soil water diffusivity can be estimated spatially using a sensor network.•Soil water content under olive tree ...canopy is lower than in the open in dry periods.
Despite the well-accepted value of soil hydraulic properties for describing and modeling matter and energy fluxes in the unsaturated zone, their accurate measurement across scales is still a daunting task. The increasing availability of continuous soil water content measurements at discrete points in space, as provided by sensor networks, offers still unexplored possibilities for evaluating soil physical properties across landscapes. In this study, we propose a new method, based on the Bruce and Klute equation, to estimate effective soil water diffusivity from soil water profile data observed during continuous desiccation periods. An analytical expression is proposed for the diffusion-soil water relationship, assuming an exponential relationship between soil water content and the Boltzmann variable. The method has been evaluated using soil water profile data observed at inter-row and under canopy locations across a rainfed olive orchard in SW Spain. The spatial variability of the effective soil water diffusivity across the orchard was estimated. Different soil conditions under the tree canopies as compared to inter-row areas resulted in significantly different effective diffusivity relationships, reflecting the effect of trees on soil physical properties and water dynamics across olive orchards. The proposed method offers a suitable alternative to traditional laboratory methods and can be easily extended to estimate soil hydraulic conductivity and water retention curves.
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