Wim Cornelis

Seasonal Predictability of Daily Rainfall Characteristics in Central Northern Chile for Dry-Land Management

Abstract The seasonal predictability of daily winter rainfall characteristics relevant to dry-land management was investigated in the Coquimbo region of central northern Chile, with focus on the seasonal rainfall total, daily rainfall frequency, and mean daily rainfall intensity on wet days at the station scale. Three approaches of increasing complexity were tested. First, an index of the simultaneous El Nino–Southern Oscillation (ENSO) was regressed onto May–August (MJJA) observed precipitation; this explained 32% of station-averaged rainfall-amount variability, but performed poorly in a forecasting setting. The second approach used retrospective seasonal forecasts made with three general circulation models (GCMs) to produce downscaled seasonal rainfall statistics by means of canonical correlation analysis (CCA). In the third approach, a nonhomogeneous hidden Markov model (nHMM) driven by the GCM’s seasonal forecasts was used to model stochastic daily rainfall sequences. While the CCA is used as a downsc...

Effects on pesticide spray drift of the physicochemical properties of the spray liquid

This research was on the effect of the physicochemical properties of the spray liquid on pesticide spray drift. Ten pesticide spray liquids with various physicochemical properties were selected for study. Some of these spray liquids were also examined with the addition of a polymer drift-retardant. In the first part, laboratory tests were performed to measure surface tension, viscosity, evaporation rate and density of the spray liquids. Subsequently, drift experiments were performed in a wind tunnel. From the results it was found that the dynamic surface tension is a major drift-determining factor, and also that the addition of a polymer drift-retardant can reduce drift significantly by increasing the viscosity. Drift reduction was found to be less effective with spray liquids of emulsifiable and suspendable formulation types than with spray liquids of water-dispersible granules and powders.

The Use of the Marasha Ard Plough for Conservation Agriculture in Northern Ethiopia

Indigenous tillage systems are often undervalued in conservation agriculture (CA). In Ethiopia, since the 1970s there have been several attempts to develop and implement often major modifications to the marasha, the traditional ox-drawn ard plough, with the main aim of creating various types of surface depressions. The establishment of furrows and ridges increases soil moisture and grain yield and reduces soil loss. Dissemination of the modified tools, however, remains limited. Recent tendencies are towards testing relatively simple conservation agriculture tools. Major challenges remain, however; the need for capacity building and problems in marketing the tools. From experimental plots, often worked with exotic tools, there is a long road to real adoption by farmers. Rather than developing yet another CA tool, we investigate whether CA-based resource-conserving technologies might be achieved successfully with simple changes to the use of the marasha. On-farm observations on traditional conservation techniques were carried out throughout the northern Ethiopian highlands, and experiments were conducted involving resource-conserving technologies. Farmers traditionally use the marasha ard plough for various types of in situ soil and water conservation by creating surface depressions, either at the moment of sowing (terwah, derdero) or after crop emergence (shilshalo). Building upon this indigenous knowledge, we further developed resource-conserving technologies into a system named derdero+, whereby the traditional ard plough was found suitable for a “bed-and-furrow” system. From the socio-economic point of view, implementation of permanent beds and retention of stubble leads to decreased oxen (and straw) requirements, but also to an increased need for weeding in the first years. To overcome that problem, we introduced glyphosate herbicide into the tillage system. The decreased runoff (−51%) and soil loss (−81%) allow protection of the downslope areas from flooding, but soil nutrient build-up and soil structure improvement are slow processes, and hence the full benefit of the permanent bed system can only be expected after some years. Overall, this type of resource-conserving technology can be part of the ongoing intensification process which includes physical soil and water conservation, slope reforestation and irrigation development. It has, however, its own niche: the cropped land sensu stricto, i.e. the most important part of the land, both for the farmer and for a nation that is striving for long-term food security.

Effect of termite mound material on the physical properties of sandy soil and on the growth characteristics of tomato (solanum lycopersicum L.) in semi-arid Niger

This investigation assessed the effects of termite mound material (TMM) on the physical properties of sandy soil and on tomato (Solanum lycopersicum L.) growth characteristics and water use efficiency. TMM combined with organic manure, TMM combined with rice straw mulching and organic manure, organic manure alone (OM) and unamended (T0) were the treatments used. Results showed that soil treated with TMM had more clay sized particles and organic carbon content than T0 and OM. In TMM-treated soil, more water was being retained at both field capacity and permanent wilting point. The application of TMM did not affect the amount of plant available water. Saturated hydraulic conductivity also remained unaffected by the TMM application, but increased with the organic matter treatment. Tomatoes grown in TMM amended soils had greater plant height and more leaves, fruit and biomass. No specific rate of TMM application was better for all parameters being assessed. The amount of water used by the tomatoes was significantly correlated (P < 0.01) with fresh fruit yield (r = 0.82), leaf area index (r = 0.82) and total dry matter production (r = 0.68). While TMM did not specifically affect plant water-use efficiency, this parameter was generally improved in amended soils.

Wind tunnel study on rough and smooth surface turbulent approach flow and on inclined windscreens

Abstract The floor of a wind tunnel was provided with isolated roughness elements in the form of small wooden blocks to increase the boundary layer thickness. Since previous experiments were carried out with a smooth floor, the results of the previous research on vertical screens with smooth surface turbulent flow could be compared with the results of the current research on vertical screens with rough surface turbulent flow. It follows that windbreaks are less effective for rough than for smooth turbulent flow, although differences depend on the open area of the windbreak. Furthermore, experiments in the wind tunnel were carried out to compare the effects on wind velocity reduction of vertical and inclined screens. Windscreens were inclined at 30, 45 and 60° with the vertical, either with or against the wind. Except the 30° windward inclined screen with an open area of 49·1% (material C), all other inclined screens were less effective compared with their vertical position, purely through the smaller vertical height of the inclined screens. In general, screens inclined against the wind were more effective than screens inclined with the wind. However, the effectiveness of the windward inclination of the less permeable windbreaks (materials A and B) was more pronounced.

Pedotransfer functions to predict water retention for soils of the humid tropics: a review

SUMMARY Over the past three decades, pedotransfer functions (PTFs) have been widelyused by soil scientists to estimate soils properties in temperate regions in responseto the lack of soil data for these regions. Several authors indicated that littleeffort has been dedicated to the prediction of soil properties in the humid tropics,where the need for soil property information is of even greater priority. The aimof this paper is to provide an up-to-date repository of past and recently publishedarticles as well as papers from proceedings of events dealing with water-retentionPTFs for soils of the humid tropics. Of the 35 publications found in the literatureon PTFs for prediction of water retention of soils of the humid tropics, 91 % of thePTFs are based on an empirical approach, and only 9 % are based on a semi-physical approach. Of the empirical PTFs, 97 % are continuous, and 3 % (one) is acla ss PTF; of the empirical PTFs, 97 % are based on multiple linear and polynomialregression of n

Effect of Root Density on Erosion and Erodibility of a Loamy Soil Under Simulated Rain

Abstract Although both aboveground and belowground components of vegetation act together in reducing soil erosion, mainly the aboveground component has received attention in past research. The aim of this study was to evaluate the contribution of roots in soil erosion control and the effect of root density in soil erodibility and soil physical properties. Perennial ryegrass (Lolium perenne L. Hugo) was grown in soil pans, and laboratory rainfall simulation experiments were conducted after 4, 8, 12 weeks of their growth with seeding density of 50 kg ha−1, after 4 weeks for seeding density of 100 kg ha−1, and on a control. The experiments with ryegrass were done in the presence of complete plants and after clipping off the shoots. Roots of ryegrass grew rapidly, attaining densities of 0.614 kg m−2 and 2.280 kg m−2 in 4 and 12 weeks, respectively. With increasing root density, splash and wash decreased exponentially. There was positive correlation between soil shear strength and root density, but no influence of roots on bulk density and saturated hydraulic conductivity was observed.

Compost Amendment to Sandy Soil Affects Soil Properties and Greenhouse Tomato Productivity

Sandy soils, with low productivity, could be improved by compost application to sustain crop production. This study aimed to examine the effect of three compost types (vegetable, fruit and yard waste compost, garden waste compost, and spent mushroom compost) on basic properties of a loamy sand and greenhouse tomato productivity. Disturbed and intact soil samples were taken from a decade-long compost field experiment on loamy sand with three compost types at application rate of 30 m3 ha−1 yr−1 (7.5 ton ha−1 yr−1). The soils were characterized for chemical and physical properties. Tomato was planted in a greenhouse using soil samples from the field and vegetative and yield parameters (plant height, stem diameter, leaf number, and fruit yield), water productivity, and harvest index were evaluated. All compost types significantly increased soil total carbon, total nitrogen, pH, electrical conductivity and significantly decreased bulk density, with no effect on plant available water compared to the control. Fresh and dry fruit weights were significantly increased after compost addition. Plant height, leaf number, stem diameter, and total biomass did not significantly improve after compost addition. Spent mushroom compost had greater effect in improving tomato productivity. A decade-long application of composts on loamy sand improved basic chemical and physical properties which were reflected in increased fruit yield in tomato. Since no negative effect of compost was observed, we suggest that sandy soils may serve as a safe end use option for these composts and potentially support crop growth.

Methodological perspectives on the application of compound-specific stable isotope fingerprinting for sediment source apportionment

PurposeCompound-specific stable isotope (CSSI) fingerprinting of sediment sources is a recently introduced tool to overcome some limitations of conventional approaches for sediment source apportionment. The technique uses the 13C CSSI signature of plant-derived fatty acids (δ13C-fatty acids) associated with soil minerals as a tracer. This paper provides methodological perspectives to advance the use of CSSI fingerprinting in combination with stable isotope mixing models (SIMMs) to apportion the relative contributions of different sediment sources (i.e. land uses) to sediments.Results and discussionCSSI fingerprinting allows quantitative estimation of the relative contribution of sediment sources within a catchment at a spatio-temporal resolution, taking into account the following approaches. First, application of CSSI fingerprinting techniques to complex catchments presents particular challenges and calls for well-designed sampling strategies and data handling. Hereby, it is essential to balance the effort required for representative sample collection and analyses against the need to accurately quantify the variability within the system. Second, robustness of the CSSI approach depends on the specificity and conservativeness of the δ13C-FA fingerprint. Therefore, saturated long-chain (>20 carbon atoms) FAs, which are biosynthesised exclusively by higher plants and are more stable than the more commonly used short-chain FAs, should be used. Third, given that FA concentrations can vary largely between sources, concentration-dependent SIMMs that are also able to incorporate δ13C-FA variability should be standard operation procedures to correctly assess the contribution of sediment sources via SIMMs.ConclusionsThis paper reflects on the use of δ13C-FAs in erosion studies and provides recommendations for its application. We strongly advise the use of saturated long-chain (>20 carbon atoms) FAs as tracers and concentration-dependent Bayesian SIMMs. We anticipate progress in CSSI sediment fingerprinting from two current developments: (i) development of hierarchical Bayesian SIMMs to better address catchment complexity and (ii) incorporation of dual isotope approaches (δ13C- and δ2H-FA) to improve estimates of sediment sources.

Particle size distribution models for soils of the humid tropics

PurposeStandardisation of particle size distribution (PSD) is a prerequisite to achieve compatibility of soil data among various countries with different texture classification systems. Therefore, several mathematical models have been proposed to accurately represent PSD. Previous studies evaluated the performance of such models to describe PSD of soils from temperate regions. This study aims at evaluating the performance of models for describing PSD of soils from the humid tropics based on a large dataset.Materials and methodsA dataset of 1,412 soils from Central Africa representing 11 different FAO Soil Groups was used. Ten PSD models with two to four fitting parameters were selected: simple log-normal (LN_2p), van Genuchten-type1 (VG_2p), van Genuchten-type2 (vG_3p), Fredlund-type1 (F_3p), Fredlund-type2 (F_4p), Weibull (W_3p), Skaggs (Sk_3p), Gompertz-type1 (G_2p), Gompertz-type2 (G_4p) and Andersson (A_4p). The fitting performance of the PSD models was evaluated by three statistical indices: the adjusted coefficient of determination, the Akaike information criterion and the relative error. Clustered columns and box plots were also used to get more insights. The predictive ability of the best PSD models was tested using a leave-one-out method and 1:1 plots.Results and discussionA table of initial values for the fitting parameters of each PSD model was provided for future applications. Some models like VG_2p, VG_3p, Sk_3p and G_4p were not suitable to describe PSD of soils in the humid tropics. On the other hand, F_3p, F_4p, W_3p and A_4p models showed outstanding fitting performance. The fitting performance of PSD models was also dependent of the textural class, the broad textural group and the bimodal character of the soil. For the most frequent textural classes in the dataset, the F_3p and A_4p models were the best closely followed by the W_3p model. While the F_3p model performed better than the A_4p model for coarse-textured soils, the opposite was observed for fine-textured soils. The W_3p model showed acceptable fitting performance for fine, medium and coarse-textured soils. The performance of the PSD models was found to be better for bimodal soils, which are common in the humid tropics, than for unimodal soils.ConclusionsGreat differences in fitting and prediction performance were found between the PSD models. Soil texture as well as the bimodal character of the soil significantly affect their respective performance. Some models like VG_2p, VG_3p, Sk_3p and G_4p are not suitable to describe PSD of soils of the humid tropics. On the other hand, F_3p, F_4p, W_3p and A_4p models showed outstanding fitting performance. Therefore, they are highly recommended in order to get a better description of the PSD of soils of the humid tropics.