Abraham Joel

Influence of aspect and slope gradient on hydraulic conductivity measured by tension infiltrometer

A tension infiltrometer technique was used to characterize differences in hydraulic conductivity (K) in two rain-fed hillsides (north-facing and south-facing) in central Chile. For the north-facing locations, smaller values of K (at a range of supply water pressure heads ψ) compared with south-facing locations were found, with accentuated differences close to saturation (zero pressure head). The differences were attributed to differences in texture and organic matter contents observed for the two sites. Furthermore, K(ψ) had a tendency to increase with increasing slope gradient. This tendency was to an extent explained by the deviation from requirements of measurements on level ground. The differences found in K(ψ) between different slope gradients were explained by the differences in the vertical and lateral hydraulic conductivity and by the occurrence of surface sealing in low slope plots. Copyright

Infiltration Rate and Hydraulic Conductivity Measured with Rain Simulator and Disc Permeameter on Sloping Arid Land

The objective of the study was to examine relationships between steady infiltration rates and hydraulic conductivity obtained with drip infiltrometer and disc permeameter on moderately to strongly sloping land. The disc permeameter is generally used for measurements on horizontal or slightly sloping surfaces but is easier to handle in the field than the drip infiltrometer. At two sites on natural prairie in Central Chile, a portable drip infiltrometer was used to measure infiltration rate and simulate rain, including the impact of falling drops, using two strategies: (1) DIH starting with a high application rate and decreasing it until a minimal application rate that generated steady runoff was obtained, and, (2) DIL starting with a low rate and increasing it until steady infiltration rate that did not increase was ensured. In parallel, a disc permeameter was used to determine infiltration rate (PI) and hydraulic conductivity (K) at different supply water pressure heads ( é ). Infiltration rates obtained with the DIL strategy were on average only 46% of those of DIH. Application intensity, particularly at the start of events, was crucial in the impact on structural changes in the soil surface. The drip infiltrometer DIH was larger than or equal to the disc permeameter PI and K at é = -20 mm. The DIL corresponded with PI at é = -40 mm and - 60 mm and K at é = -30 mm. Disc permeameter was shown to be a useful tool as an alternative to drip infiltrometer to determine infiltration rates even on moderately to strongly sloping land, if measurements with the former are carried out at some predefined as é identified in this article.

Methods to Estimate Lettuce Evapotranspiration in Greenhouse Conditions in the Central Zone of Chile

This study evaluates five methods to estimate crop evapotranspiration in greenhouse conditions. It compares their performance in relation to the evapotranspiration directly determined from water balance measurements (ETlys) in an irrigated lettuce (Lactuca sativa L.) crop during 9 weeks. Daily values of the reference evapotranspiration (ETo) from Class A pan (CAP), Piche atmometers (ATM), Andersson evaporimeters (ANE), FAO-Radiation (FRE) and FAO-Penman-Monteith (PME) equations were compared. The methods showed similar temporal variations but at different ranges as follows: ANE < CAP < FRE < PME < ATM. Furthemore, ETo had a clear correlation with solar radiation. Crop coefficients (Kc = ET lys/ETo) varied somewhat amongst the methods, but trends were identified for two periods: in the first week, the overall mean Kc was 0.3 (± 0.1) and in weeks 2 to 9 on average 0.6 (± 0.3). The greenhouse values of Kc were lower than those generally adopted for lettuce in field conditions. In terms of irrigation design, crop evapotranspiration can be estimated by the methods in this study, on the condition that the appropriate crop coefficients are applied. The fact that ANE showed values closest to those of ET lys, along with cost and management convenience, makes it an advantageous alternative as compared to the other methods.

Method for in situ measurements of water, sediment and phosphorous transport in the upper soil profile

Abstract Research on transport processes involved in P losses by subsurface flow, including artificial drainage, is becoming increasingly important. An improved understanding of the processes involved in sediment detachment and P mobility in the soil profile is needed in order to develop proper management strategies for P control. The objective of this article is to present the development of a field lysimeter technique, and a complementary laboratory pinhole test on undisturbed soil samples, that can be used to assess rates and mechanisms involved in water, sediment and phosphorus transport in the upper soil profile at different rainfall intensities. The study, performed on a silty clay, consisted of three parts: (1) pre-test of a new field lysimeter approach with the aim to observe water flow patterns and difficulties related to preparation and set-up, (2) evaluation of the improved field lysimeter methodology, which consisted of a rain simulator above ground, the soil profile through which the applied water percolated, and a collection tray at 40–50 cm depth from which the drain water and sediment was sampled, (3) evaluation and development of the pinhole test for assessing soil resistance to internal erosion. The pre-tests gave promising results and the improved field lysimeter showed interesting temporal responses, at two consecutive rain simulation intensities, in outflow rates of water, bromide, lithium, total P and dissolved P. The pinhole test was run on undisturbed samples with three different water contents and at three different applied positive pressure heads and showed fast peaks in turbidity following start of each run. Combining measurements from the in situ field lysimeter and pinhole approaches presented in this article has the potential to be valuable in detecting critical parameters that control the processes leading to subsurface leaching of P to deeper soil layers.

Influence of higher rain intensities on phosphorus movements in the upper half meter of macroporous clay soil

In climate change scenarios, the frequency of high-intensity rain events in Sweden is assumed to increase. In a plot experiment at Ultuna, Uppsala, the influence of rain intensities on phosphorus (P) transport in the uppermost 0.5 m of a clay soil was studied at 16 locations. A rain simulator, 0.5 × 0.5 m and mounted 1 m above the soil surface, was used to simulate 85–500 min rain sequences causing small (4–9 mm h−1) and large (22–28 mm h−1 and one extreme at 37 mm h−1) steady water fluxes (intensity) in the underlying soil profile. Water percolated to a zero-tension collector tray at 0.5 m depth where drain water and its sediment load was sampled at discrete time intervals. The total P (TP) mass flux ranged, at low intensity, between 12–92 μg m−2 min−1 (average 28.1 μg m−2 min−1) and, at high intensity, between 83–375 μg m−2 min−1 (average 168.5 μg m−2 min−1) and 648 μg m−2 min−1 at the extreme intensity. The soluble reactive (inorganic) P (SRP) mass flux ranged, at low intensity, between 1–65 μg m−2 min−1 (average 10.0 μg m−2 min−1) and, at high intensity, between 6–205 μg m−2 min−1 (average 47.9 μg m−2 min−1) and 495 μg m−2 min−1 at the extreme intensity. Thus, in the intensity range 4–28 mm h−1, TP and SRP increased, on average, by approximately 12% (μg m−2 min−1) per unit increase in intensity (mm h−1). The results of this study demonstrate increased sediment and P loss/mobility for clay soil under increased precipitation intensity predicted under climate change.

Maize root development and grain production as affected by soil and water management on a sandy soil in a semi-arid region of southern Mozambique

ABSTRACT Average yield of maize (Zea mays L.) in Mozambique is low, mainly due to low use of inputs in agriculture, high seasonal rainfall variability and inadequate soil preparation. A study conducted in two summer crop seasons (November–March 2012/2013 and 2013/2014) examined the impact of three tillage methods (hand hoeing, strip tillage and conventional tillage), two fertiliser levels (0 and 40% N) and two water supply regimes (rainfed and irrigated) on maize root development and grain yield on a sandy soil in a semi-arid region of Mozambique. Tillage had a major effect on soil penetration resistance, but little effect on root growth and limited effect on yield. Thus, there appears to be little need for loosening on this soil. There was also no interaction between tillage and the other experimental factors, meaning that tillage system can be chosen irrespective of fertiliser and water supply. Irrigation had the largest impact on root and shoot growth and crop yield, increasing yield in season 2 from 670 to 4780 kg ha–1.There was a very strong interaction between fertiliser and water supply, with no yield increase for fertiliser in the rainfed treatment, while combined with irrigation it increased yield by 1590 kg ha–1 in season 1 and 1840 kg ha–1 in season 2. Thus, for the conditions studied here, it was rational to add fertiliser only in combination with irrigation and not in a rainfed system.

Effects of tile drainage repair on nutrient leaching from a field under ordinary cultivation in Sweden

Leaching losses of nitrogen (N), phosphorus (P) and potassium (K) from arable land can be high, with N and P contributing significantly to the eutrophication of lakes and coastal waters. This study examined whether agriculture management and drain repair changed the chemical properties of shallow groundwater and affected nutrient leaching in the field. The hydrology of a subsurface-drained agricultural observation field included in the Swedish water quality monitoring programme was simulated for the period 1976–2006 using the process-based, field-scale model DRAINMOD. On the assumption that the drainage system operated similarly before and after repair, 54% more water was assigned to low-moderate flow events. Measured concentrations of sulphate-sulphur (SO4-S), sodium (Na), chloride (Cl) and potassium (K) were significantly lower in shallow groundwater in the period before drainage system repair (1980–1998) than afterwards (1998–2010). The concentrations were also significantly correlated with the corresponding concentrations in near-simultaneously sampled drain water. A similar connection was not observed for Na and Cl in the period before drain repair. Elevated concentrations of nitrate-nitrogen (NO3-N) were recorded both in shallow groundwater and in drainage water from 1998 to 2010, especially after incorporation of chicken manure into the soil in 1998. Based on simulated discharge (assuming a functioning measuring station throughout), estimated flow-weighted mean NO3-N concentration in drainage water increased from 5.6 mg L−1 (1977–1998) to 15.7 mg L−1 in the period 1998–2000. Simultaneously, mean NO3-N concentration in shallow groundwater increased from 0.2 to 4.0 mg L−1, and then to 4.8 mg L−1 in the period 2000–2012. It was estimated that after drain repair, a greater proportion of infiltrated NO3-N entered the receiving stream directly via the outlet of the tile drainage system close to the fields monitoring station than was the case before repair.

Pathogens in crop production systems irrigated with low-quality water in Bolivia

In dry areas, the need for irrigation to ensure agricultural production determines the use of all available water sources. However, the water sources used for irrigation are often contaminated by untreated or minimally treated wastewater. Microbial risks from reusing wastewater for vegetable irrigation can be addressed by installing environmental barriers that pathogens must cross to reach humans in the reuse system. Knowledge of pathogen flows inside the system and pathogen removal potential is the first step towards devising a risk management strategy. This study assessed microbe prevalence in farming systems in the Bolivian highlands that use wastewater-polluted sources for irrigation of lettuce. Samples of soil, lettuce and different water sources used in the farming systems were taken during one crop season and concentrations of coliphages, Escherichia coli and helminth eggs were measured. The results showed high spread of these microorganisms throughout the whole system. There was a significant correlation between microbial quality of water and of the harvested produce for several microorganisms. The microbial prevalence in protected shallow wells was found to be significantly lower than in other water sources. These findings can help formulate feasible risk management strategies in contexts where conventional technologies for microbial removal are not possible.

Status assessment of agricultural drainage ditches

Abstract. Poor maintenance, environmental concerns, land use changes, and adaptation to climate change are creating a growing need for better agricultural drainage. The objectives of this study were to identify ditch properties that can be evaluated visually on-site and related soil erosion processes, and to define parameters requiring more intensive study and estimate these using simplified methods. The study included surveys of ditches in various soils using MADRAS (Minnesota Agricultural Ditch Research Assessment for Stability) to classify the status of these ditches. To explain why some ditch sections were in poor condition, additional field and laboratory studies were carried out. Soil samples were taken for analysis of particle size distribution, near saturation shear strength (VJ Tech), and cohesion strength. The data model HEC-RAS was used for simulation of hydraulic forces acting at different flow rates. Digital maps of land use in the catchment area in different years were used to estimate changes in runoff conditions over time. MADRAS proved to be a suitable tool for rapid assessment of stability problems in ditches. HEC-RAS simulations were a good complement to MADRAS in assessing how changes in land use affected the hydraulic load and in highlighting bottlenecks in systems. However, the hydraulic load did not adequately explain the degradation degree in some ditch sections. Measurements of soil shear strength were a good aid to understanding existing degradation. Thus assessment of sensitivity to erosion and bank failure are essential in anticipating the risks of future erosion processes in ditches.

In Situ Method for Measuring Water Fluxes, Sediment, and Phosphorus at High Drip Infiltrometer Intensities in the Upper Half Meter of a Tilled Clay Soil

The first step in evaluating phosphorus (P) loss risks should be to investigate the topsoil, which is generally considered a source of P transport via macropore flow. A procedure is presented for in situ measurement of hydraulic response times, critical water outflow rates, as well as turbidity (T), sediment (SC), and total phosphorus (Ptot) concentrations in outflowing soil water solution from the upper half meter of a clay soil. The method applies to a range of controlled experimental rainfall intensities from a drip infiltrometer, and a zero-tension collection tray located at 0.5 m depth through which percolating water/sediment solution is sampled. Reasonable positive relationships were observed between T, SC, and Ptot versus steady output flow rates (qs). Dependencies were strong between Ptot and each of qs and T, and weaker between Ptot and SC. The methods require further validation and will be further developed in upcoming studies.