Jacques Gallichand

Effect of increased fertilizer applications to wheat crop on soil-water depletion in the Loess Plateau, China

Winter wheat monoculture occupies a large area of the Loess Plateau dryland region of China. Its yield is mainly limited by available water and fertilization. From the mid-1980s, yield of winter wheat increased with fertilizer application, and this increased productivity may increase soil-water depletion and reduce available soil-water at planting. Besides rainfall during the growing season, an important source of water for the crops is stored soil-water at planting. In the long run, increasing fertilization may not be sufficient to maintain higher yield. To develop better dryland crop and water management practices, a 15-year experiment of winter wheat monoculture was conducted at the Changwu Agri-ecological Station of the Loess Plateau from 1984 to 1999. Different levels of productivity were implemented by the application of chemical fertilizers and manure. The experimental design consisted of a control treatment (CTL) and three fertilizer treatments: nitrogen, phosphorus and manure (NPM), nitrogen and phosphorus (NP), and manure (M). Compared to CTL, on average, treatments NPM, NP and M increased yield by 148, 110 and 59%, and decreased soil-water at planting by 102.6, 59.1 and 31.6 mm within the 300 cm profile, and soil-water at harvest by 142.3, 102.5 and 70.2 mm, respectively. There was a decrease of soil-water with time for fertilizer treatments. Crop yield with high fertilization treatments responded more to rainfall variations. Considering the importance of soil-water at planting for crop yield in dryland farming, winter wheat monoculture with high fertilization does not appear to be a sustainable management practice in the Loess Plateau dryland region of China.

Mapping clay content for subsurface drainage in the Nile delta

Abstract Drain envelope requirements for large-scale subsurface drainage projects are often estimated based on the surface area with clay percentages less than a given threshold value. Contouring clay percentage data can be done by computer using spatial interpolation methods. Cross-validation was used to evaluate the precision of estimation for clay percentage using five interpolation techniques (closest neighbor, moving average, weighted moving average, kriging, and cokriging) for a study area of 33,500 ha in the Nile Delta. The clay content was measured at 485 sites. Cokriging used the correlation between clay percentage and saturated hydraulic conductivity, which had been measured at 3488 sites. The lowest mean absolute difference (MAD) between observed and interpolated clay percentage values was obtained for cokriging (12.01). MAD values were very close to that of cokriging in the case of moving average (12.13), weighted moving average (12.23), and kriging (12.21), whereas for the closest neighbor method a MAD value of 16.44 was obtained. Surface areas under 30 and 40 percent clay were over-estimated for the closest neighbor method, and under-estimated for the moving average method. Surface areas and contour maps based on weighted moving average, kriging, and cokriging were very similar. Use of moving average resulted in a loss of precision due to the smoothing effect.

An evaluation of EPIC soil water and yield components in the gully region of Loess Plateau, China

The Erosion and Productivity Impact Calculator (EPIC) has been used to determine the effect of different cropping systems and management practices on soil productivity in the Loess Plateau of China. However, its crop growth and soil water balance submodels have not been verified in this region. The objective of the present study was to evaluate the ability of EPIC to estimate soil water content (θ in m 3 /m 3 ), seasonal evapotranspiration (ET in mm/season) and crop yield ( Y in t/ha) for winter wheat and maize. A 20-year field experiment was conducted at the Changwu Agro-ecological Experimental Station of the Loess Plateau, and divided into a calibration period and a validation period. Data from calibration (1984–94) were used to optimize the four most sensitive parameters of the EPIC crop yield submodel, whereas data from 1994 to 2004 were used for validation. For both crops, there were no significant differences between measured and estimated long-term means of the three variables ( P =0·05) for either the calibration or validation periods. EPIC estimated all three variables with a small relative root mean square error (RRMSE), i.e. the ratio of root mean square error to the mean value. For wheat and maize, the calibration period resulted in respective RRMSE values of 0·112 and 0·100 for θ, 0·121 and 0·116 for ET, and 0·135 and 0·147 for Y. During the validation period, the RRMSE values obtained were 0·090 and 0·085 for θ, 0·129 and 0·135 for ET, and 0·169 and 0·149 for Y, for wheat and maize, respectively. The performance of EPIC in estimating annual values of θ, ET and Y was variable. For validation, EPIC explained 65, 79 and 64% of the measured variations of θ, ET and Y, respectively, for wheat, and 60, 70 and 67% for maize. The EPIC-estimated long-term average values of the three variables were not significantly different from measured values for winter wheat and maize during the calibration and validation periods. It can therefore be used in the gully region of the Loess Plateau to define alternative cropping systems and management practices.

Investigation of turbulence characteristics in channel with dense vegetation

Abstract In this experimental study, the turbulent flow in a channel with vegetation by using sprouts of wheat on channel bed was investigated. Two different aspect ratios of channel were used. An Acoustic Doppler Velocimetry was used to measure parameters of turbulent flow over submerged sprouts of wheat, such as velocity profiles. The log law and the Reynolds shear stress distribution were applied. Results indicate that the position of the maximum turbulence intensity superposes on the inflection point situated over the top of submerged vegetation cover. Quadrant analysis shows that near the vegetation bed, the sweeps and ejections appear to be the most dominant phenomenon, while far from the vegetated bed, the outward is dominant event. Results also show that the aspect ratio plays an important role on the contribution of the different bursting events for Reynolds stress determination.

Solute transport in sub-irrigated peat-based growing media

New legislation to reduce the amount of fertilizer leached into the environment by horticultural growers and the need to implement water-saving irrigation systems require an understanding of salt build-up and of nutrient cycles in order to develop efficient water-use strategies for growers. Solute transport in growing media is central to this process, but has received little attention thus far. The objectives of this study were to determine how solutes behave in sub-irrigated growing media and to assess a solute transport model for these media. A steady state evaporation (upward water flow) experiment was carried out with three different growing media in packed columns in the laboratory. Bromide, potassium and copper concentrations were determined using in-column pore water solution samplers and by sectioning the columns at the end of the experiment to obtain concentration profiles. The Hydrus-1D model was fitted to the solution sampler data assuming non-linear Freundlich adsorption, and then used to obta...

Effects of accelerating and decelerating flows in a channel with vegetated banks and gravel bed

Abstract Experiments were conducted in an 8 m long, 40 cm wide, and 60 cm deep re-circulating flume with vegetated banks and gravel bed to study the effects of accelerating and decelerating flows on the flow structure. Significant dip phenomenon was observed in velocity profiles under decelerating flow and the velocity defect law was not suitable due to the effect of vegetated banks. Near the vegetated banks, the turbulence intensities illustrated convex distribution for both accelerating and decelerating flows. Application of quadrant analysis revealed that the effect of vegetated banks is important on the flow structure and the Reynolds stress distribution. Accelerating and decelerating flows did not show a significant difference on percentage of time occupied by each kind of turbulent event within bursting cycle, but affected the shape of joint probability distributions of turbulent intensities in the horizontal and vertical directions.

Optimal sampling density of hydraulic conductivity for subsurface drainage in the Nile delta

Abstract The density of hydraulic conductivity measurements is of primary importance for the design of large-scale subsurface drainage projects. This study was conducted to investigate the effect of sampling density on hydraulic conductivity estimation, and to determine the optimal sampling density using results of 3488 hydraulic conductivity tests from a 33 500 ha subsurface drainage project in the Nile Delta of Egypt. Kriging was used to obtain hydraulic conductivity point and block estimates based on the original 300 m sampling grid and on reduced sampling grids with spacings of 600, 900, and 1200 m. Kriged estimates from the complete grid were compared to those from reduced grids. The correlation coefficient between kriged estimates of block hydraulic conductivity based of the 300 m versus the 600 m measurement grid was larger than 0.90, which indicates that the optimal sampling grid spacing is in the order of 600 m. Slopes of the estimation standard deviation versus sampling density showed that the optimal sampling grid spacing was between 400 and 600 m, and could be determined from sampling grids with a spacing of 900 m or less. It appears that, for the Nile Delta, the optimal sampling density of hydraulic conductivity can be determined from a preliminary survey with a grid spacing of 900 m.

Field investigation on friction factor in mountainous cobble-bed and boulder-bed rivers

Abstract This paper presents results of the friction factor of cobble-bed and boulder-bed rivers based on 23 field measurements in three mountainous rivers in Iran. Results reveal that features of our measured velocity profiles in boulder-bed rivers in mountainous region do not present a specific shape but illustrate specific pattern in cobble-bed rivers. This difference is attributed to scale effect of relative submergence. It is found that the relative submergence in cobble and boulders-bed rivers is the only key parameter that influences friction factor estimation and other parameters such as particle Froude number and Froude number have few impacts on flow resistance of cobble-bed and boulder-bed rivers. The proposed relationship for estimation for the friction factor should be useful for large coarse-bed rivers.

Modeling Sediment Movement into Perforated Subsurface Drains

ABSTRACT IN order to predict the amount of sediment in subsur-face drain pipes, an analogy was established between the drain cross sectional area occupied by sediment and the amount of granular material that flowed in a confined volume through a perforation before a bridge formed. Experiments were performed using glass beads and eight different types of sand using a permeameter-like apparatus. Various parameters related to the shape and dimension of the perforations and to the particle size distribution of the sands were investigated. Results indicate that a sigmoid model describes more accurately than a linear model the relationships between the amount of material and the various factors related to the geometry of the perforation. For the eight sand types, the amount of material is best predicted (R2 = 0.828) from the hydraulic radius of the perforation and from the D60 of the sand.

Soil sample preparation techniques on routine analyses in Quebec affect lime and fertilizer recommendations

Abstract: Inadequate and (or) inconsistent soil sample preparation techniques (SPT) contribute to excessive variance, difficulties in soil test interpretation, and incorrect lime and fertilizer recommendations. The objective of this study was to evaluate the effect of SPT of five laboratories in Quebec (Canada) on chemical parameters measurement reliability. Samples of fine (G1), medium (G2), and coarse (G3) textured soils were collected from the surface layer. Three 500 g portions of each soil were sent to each laboratory for preparation. In addition, all samples were analyzed by the same laboratory for routine analyses. Nested ANOVA in a hierarchical model were performed with components of SPT interlaboratory reproducibility, SPT intralaboratory replicability, and intralaboratory soil analysis repeatability. Before samples were analyzed, we observed an important interlaboratory heterogeneity of particle size distributions for the same samples; due to sample preparation techniques, this can affect results of the analyses. Of all variables analyzed, the only significant, outside acceptable variations due to SPT were (1) pHwater in G1; (2) PM-III, AlM-III, and (P/Al)M-III in G1 and G2; (3) KM-III, CaM-III, MgM-III and organic matter in G3; and (4) MnM-III and CuM-III in G1, G2, and G3. The steps in SPT, mostly drying and crushing, require standardization to reduce the variance of the entire soil testing process.