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Closing the yield gap and enhancing efficiency in rainfed maize production systems in Ethiopia requires urgent action in increasing the productivity of degraded agricultural land. The degradation of land through continuous compaction and decline in the organic matter has resulted in a wide-spread formation of a hardpan that restricts deep percolation, prevents plant root development, and, ultimately can lead to increased erosion. Studies exploring practical low-cost solutions to break the hardpan are limited in Ethiopia. The main objective was to evaluate soil mechanical (i.e. modified plow or Berken plow) or biological intervention (i.e. intercropping with pigeon pea) effectiveness to enhance soil water management and crop yield of rainfed maize systems whilst reducing soil erosion and runoff. Five farm fields, each including four plots with different tillage treatments, were monitored during two rainy seasons in 2016 and 2017. The treatments were: (i) farmers practice under conventional (CT) tillage; plots tilled three times using an oxen driven local plow Maresha, (ii) no-till (NT), (iii) Berken tillage (BT), plots tilled three times using an oxen pulled Berken plow, and (iv) biological (CT + Bio), taprooted pigeon pea intercropped with maize on plots conventionally tilled. Results showed that mean tillage depth was significantly deeper in the BT (28 cm) treatment compared to CT and CT + Bio (18 cm) treatments. Measured soil penetration resistance significantly decreased up to 40 cm depth under BT and maize roots reached 1.5 times deeper compared to roots measured in the CT treatment. Under BT, the estimated water storage in the root zone was estimated at 556 mm, 1.86 times higher compared to CT, 3.11 times higher compared to NT and 0.89 times higher compared to CT + Bio. The positive effects on increased water storage and root development resulted in an average increase in maize grain (i.e. 15%, 0.95 t ha- 1) and residual above ground biomass (0.3%, 6.4 t ha- 1) leading to a positive net benefit of 138 USD ha- 1 for the BT treatment compared to the CT treatment. The negative net benefit obtained under CT and CT+Bio was mainly related to the high labor cost related to plowing, weeding, planting, and fertilizer application whilst in the NT this was related to the significantly lower maize yields. The positive effects in the BT treatment, and to some extent the CT+Bio treatment show great potential for smallholder rainfed maize systems where degraded soils with hardpans and high variability in rainfall prevail.

The authors regret that they have inadvertently made a mistake while typing the formula of the Eq. 1. The correct formula should be: [Formula presented] The calculations performed in the study are based on the correct formula and this error doesn't in no way affect any of the findings of the paper. The authors would like to apologise for any inconvenience caused.

Introduction Hydrologic modeling at daily or sub daily resolution requires accurate precipitation and temperature data, which is particularly important when planning land use changes and live management operations such as irrigation allocation. Weather gage data pose a variety of challenges, including the fact that they are nonexistent in many watersheds of interest. We show that by integrating global forecast products and reanalysis datasets from the atmospheric modeling community into the hydrologic models commonly used, we can circumvent some of the issues with point-of-measure weather gauges. Traditionally in hydrologic forecasting, a precipitation forecast is used from a nearby precipitation station on which the hydrologic model has been calibrated. Here we present the results of two studies. First, we compare calibrating a watershed model (SWAT) using weather forecasts from ensembles of raw gridded atmospheric models interpolated to the center of subbasins against using the closest weather gage measurements. Second, we perform a similar study using global reanalysis datasets. In addition, we look at what scales and radii using direct gridded model output may introduce equal or less error to watershed modeling projects than using the closest station. We demostrate: -There is validity to using reanalysis datasets in place of weather station data to force hydrologic modeling systems when nearby weather stations are not available or have inconsistent records -There is validity to using short term forecast archives in place of weather station data to force hydrologic modeling systems. -The distance to the where the model skill produces the same accuracy as the weather stations is closer than we thought. -Variables from the atmospheric models are physically linked, and we should likely keep them that way. Conclusion This study found that weather forecast archives and CFSR reanalysis data provide a potentially valuable alternative to “nearest weather station” data for hydrological modelers. Indeed, this study found that the CFSR data may actually be a better representation of the weather than point observations, at the scale of small watersheds (Presented Nov. 2011. Third International Forum on Water and Food (IFWF3). Tshwane, South Africa http://waterandfood.org/2012/04/22/third-international-forum-on-water-and-food/

Introduction Hydrologic modeling at daily or sub daily resolution requires accurate precipitation data, which is particularly important when assessing flood risk in small runoff dominated watersheds. Precipitation gage data pose a variety of challenges, including the fact that they are located outside of many watersheds of interest and thus, may not accurately represent the actual rainfall in the watershed. We show that by integrating global forecast products from the atmospheric modeling community into the hydrologic models commonly used that we can circumvent some of the issues with point-of-measure rain gauges. Traditionally in hydrologic forecasting, a precipitation forecast is used from a nearby precipitation station on which the hydrologic model has been calibrated. In this study, we compare and contrast calibrating a watershed model (SWAT) using derived statistical representations of precipitation forecasts from "poorman's" ensembles of raw gridded atmospheric models interpolated to the center of subbasins vs using the closest precipitation gage measurement and NWS forecasts for that gage location. In addition, we look at what scales and radii using direct gridded model output may introduce equal or less error to watershed modeling projects than using the closest station. Discussion -It appears there is validity to using short term forecast archives in place of weather station data to force watershed models. -The distance to the where the model skill produces the same accuracy as the weather stations is closer than we thought. -We need to further investigate the watershed calibrations independent for individual forcing data sets. -We need to be careful when applying this method, and should use statistical summaries of the ensembles sparingly. -Variables from the atmospheric models are physically linked, and we should likely keep them that way. Presented NOAA NWS Eastern Region Flash Flood Conference, 2-4 June 2010, Wilkes-Barre, PA.

[2] To explain the dynamic behavior of the matric potential at the wetting front of gravity driven fingers, we take into account the pressure across the interface that is not continuous and depends on the radius of the meniscus, which is a function of pore size and the dynamic contact angle θd. θd depends on a number of factors including velocity of the water and can be found by the Hoffman-Jiang equation that was modified for gravity effects. By assuming that water at the wetting front imbibes one pore at a time, realistic velocities are obtained that can explain the capillary pressures observed in unstable flow experiments in wettable and water repellent sands.

An approximate analytical solution of the Hairsine-Rose model of erosion is obtained by interpolation of asymptotic expressions for large times and great distances. The solution, when erosion is initiated by rainfall impact, is both simple and accurate. The results are illustrated by comparison with a numerical solution.

To understand colloid facilitated pollutant transport in vadose zone, the dynamics of wetting front needs to be understood. Wetting front dynamics is dependent on the contact angle between air-water interface and the soil grain. In this presentation we solve the Navier-Stokes Equations with COMSOL Multiphysics in a pore to develop a relationship between contact angle and the imposed pressure gradient and velocity of the wetting front. The results agree with 1975 experimental results of Hoffman.

Governing mechanisms in immobilization and mobilization of colloids in the unsaturated zone are not well understood. Recent findings show that colloids attach to the air-water-solid (AWS) interface. The interaction of the various forces and the flow field on colloids near the AWS interface is complex. In this presentation, we will determine the interaction force conditions for attachment of colloids to the AWS for flow fields consisting of flow around solid grains in the presence of and air-water system of fluids. The flow field is determined using COMSOL-MP to numerically solve the Navier-Stokes equations. The viscous drag force for the moving fluid on the colloids is then quantified from this numerical solution and the balance of this force with other field forces resulting from interfaces (solid-liquid and liquidair) is computed to determine the potential for attachment of colloids to the AWS interface. For the present study spherical solid grains are considered, while in future studies we will consider solids grains of more realistic shape.

COMSOL Multiphysics was used to simulate the transport of inert colloidal particles at the pore scale within an unsaturated micromodel consisting of sand grains and air bubbles. The unsaturated soil pore was modeled as four adjoining grains with an air bubble trapped at the center. Colloids were assumed to behave passively in the flow field since mass effects, size effects, and interfacial forces were not considered in the present analysis. A significant fraction of colloids were found to be retained within the porous media, but this occurred because those colloids were caught in stagnation zones of the flow field. Based on our result we conclude that COMSOL MP3.2 will be a valuable tool for numerically simulating colloid behavior at the micrometer scale.

Water scarcity is increasingly viewed as the principal constraint limiting agricultural production and human livelihood improvement in the rural areas of many developing countries. Policies that encourage more efficient and equitable water use - including the introduction of incentive-based water pricing systems - are an important challenge. This paper reports the results of a mathematical programming model which was constructed for the El Angel watershed in northern Ecuador with the goal of exploring the effects of several water pricing alternatives. The model incorporates farmers' crop and pasture planting and resource allocation decisions, based on maximizing regional gross margin subject to land, water, labor, seasonal, food security and other constraints. Four water pricing scenarios are examined. The results show that adequate water resources currently exist to permit a reallocation of water within the watershed, which would generate higher regional production and incomes. Several water pricing alternatives are explored which would discipline water use in those parts of the watershed where water is currently overused and unregulated. Incomes could be significantly increased in currently waterscarce parts of the watershed while generating only small reductions in production and incomes in water-abundant zones. While tradeoffs exist among economic, environmental and employment goals, significant net gains are achievable. If a differentiated system of water prices is considered to be unrealistic, a system of single seasonal prices would likely generate reduced, though significant, benefits. Introducing a system of comprehensive water charges would likely create similar benefits in other developing country watersheds facing similar resource constraints.

Water scarcity is increasingly viewed as the principal constraint limiting agricultural production and human livelihood improvement in the rural areas of many developing countries. Policies that encourage more efficient and equitable water use - including the introduction of incentive-based water pricing systems - are an important challenge. This paper reports the results of a mathematical programming model which was constructed for the El Angel watershed in northern Ecuador with the goal of exploring the effects of several water pricing alternatives. The model incorporates farmers' crop and pasture planting and resource allocation decisions, based on maximizing regional gross margin subject to land, water, labor, seasonal, food security and other constraints. Four water pricing scenarios are examined. The results show that adequate water resources currently exist to permit a reallocation of water within the watershed, which would generate higher regional production and incomes. Several water pricing alternatives are explored which would discipline water use in those parts of the watershed where water is currently overused and unregulated. Incomes could be significantly increased in currently waterscarce parts of the watershed while generating only small reductions in production and incomes in water-abundant zones. While tradeoffs exist among economic, environmental and employment goals, significant net gains are achievable. If a differentiated system of water prices is considered to be unrealistic, a system of single seasonal prices would likely generate reduced, though significant, benefits. Introducing a system of comprehensive water charges would likely create similar benefits in other developing country watersheds facing similar resource constraints.

The report examines the relationships between agricultural policies in the North China Plain, the approaches to water management that evolved from them, the quantity of water that was actually used, and the consequent groundwater depletion beneath Luancheng County, Hebei Province, from 1949 to 2000. To systematically address these relationships, we use a comprehensive water-balance approach. Our results indicate that a single, longstanding policy-that of using groundwater to meet the crop-water requirements not supplied by precipitation-is responsible for the steady rate of groundwater decline.

We explore selected aspects of J.-Y. Parlange’s contributions to hydrological transport of solutes and sediments, including both the laboratory and field scales. At the laboratory scale, he provided numerous approximations for solute transport accounting for effects of boundary conditions, linear and nonlinear reactions, and means to determine relevant parameters. Theory was extended to the field scale with, on the one hand, the effect of varying surface boundary conditions and, on the other, effects of soil structure heterogeneity. Soil erosion modeling, focusing on the Hairsine-Rose model, was considered in several papers. His main results, which provide highly usable approximations for grain-size class dependent sediment transport and deposition, are described. The connection between solute in the soil and that in overland flow was also investigated by Parlange. His theory on exchange of solutes between these two compartments, and subsequent movement, is presented. Both deterministic and stochastic approaches were considered, with application to microbial transport. Beyond contaminant transport, Parlange’s fundamental contributions to the movement of solutes in hypersaline natural environments provided accurate predictions of vapor and liquid movement in desert, agricultural, and anthropogenic fresh-saline interfaces in porous media, providing the foundation for this area of research.

We estimate the willingness-to-pay (WTP) for reliable access to irrigation water for a sample of farmers in a watershed of the Ethiopian highlands who do not have prior experience with irrigation. To address the lack of previous irrigation experience, we account for underlying expectations of future irrigation productivity using an Integrated Choice and Latent Variable (ICLV) econometric model. We then compare the ICLV estimates with alternative models that do not account for expectations regarding productivity increases with irrigation. Our results indicate that both the ICLV and alternative provide similar conclusions with respect to the mean WTP for reliable irrigation water access. However, ignoring farmers’ perceptions would understate the uncertainty of the mean or aggregate WTP. Refereed/Peer-reviewed