Elsevier

Agricultural Water Management

Volume 134, 1 March 2014, Pages 42-49
Agricultural Water Management

Soil moisture regimes under point irrigation

https://doi.org/10.1016/j.agwat.2013.11.012Get rights and content

Highlights

  • Admissible irrigation in relation to emitter discharge rates has been examined.

  • Method for location of the wetting front has been developed for point irrigation.

  • Soil–water relationships in the soil under point irrigation, has been developed.

  • Field experimental method is rapid and simple, and provides consistent results.

  • Incorrect point irrigation can cause serious environmental damage.

Abstract

The main objective of this paper is determination of principal relationships influencing the distribution of moisture content in a soil profile under an emitter in point irrigation. Research was carried out by conducting field experiments. They determined geometry of wetted soil volume in a soil profile under point irrigation. Infiltration of water from a single emitter and the resulting spatial distribution is a typical feature of localized irrigation technology. The field experiments using different emitter discharges and various periods of irrigation on haplic Luvisol (ha LV) (ALFISOLS Udalfs) on loess were conducted in a soil profile 1 m deep.

Admissible duration of irrigation in relation to discharge rates has been calculated and illustrated in a graph. Incorrect irrigation practices can cause serious environmental damage. A method for determining the width and depth of the wetted soil volume under the point irrigation was developed. This method is rapid and simple, and it gives consistent results.

Introduction

Moistened soil volumes in surface and subsurface drip irrigation systems have been measured and/or theoretically analyzed by many authors. They include Brandt et al. (1971), Bresler et al. (1971), Goldberg et al., 1971, Goldberg et al., 1976, Lomen and Warrick (1974), Keller and Karmeli (1974), Roth (1974), Ben-Asher et al. (1978), Warrick et al. (1979), Roth (1982), Amoozegar-Fard et al. (1984), Trickle irrigation (1984), Vermeiren and Jobling (1984), Clothier et al. (1985), Zazueta et al. (1995), Shwartzmann and Zur (1986), Ungureanu (1986), Shein et al. (1987), Healy and Warrick (1988), Voronin et al. (1989), Clothier and Smettem (1990), Or (1996), Zur (1996), Or and Coelho (1996), Revol et al. (1997), Coelho and Or (1997), Hoang (1998), Thorburn et al. (2003), Skaggs et al. (2004), Šimůnek et al. (2006), Singh et al. (2006), Lazarovitch et al. (2007), Qiaosheng et al. (2007), Bhatnagar and Chauhan (2008), and Elmaloglou and Diamantopoulos, 2007, Elmaloglou and Diamantopoulos, 2010.

A localized irrigation system offers unique agronomic, agri-technical, and economic advantages for efficient use of water and labor. The distribution of water in localized irrigated soils is extremely important from an agri-technical point view since it determines the boundaries of the root zone and the concentration of water and salts (Goldberg et al., 1976).

In point irrigation, water is applied to soil surface in small drip flows from an opening with a point discharge rate more than that for drip irrigation but less than 140 l/h. Point irrigation was first designed in Czechoslovakia in the 1960s of the 20th century. Point irrigation system is very similar to the system of drip irrigation. The point irrigation has been named after the method of localized water application. The water outflow points (emitters) are located on lateral tubes on or beneath the soil surface. Point irrigation has lower quality requirements of irrigation water than drip irrigation. Blockade is minimized due to the large orifices of emitters, usually from 1.6 to 2.4 mm. Therefore, mesh filters are usually sufficient for point irrigation. Point irrigation systems are thus often preferred to drip irrigation from an economic point of view. However, due to low pressure, water slows in the point irrigation systems laterals (0.04–0.12 MPa), the disadvantage is that small differences in elevation have a big influence on the discharge rate of the emitters and on irrigation uniformity. Increased discharges of emitters require larger capacity of all elements of the system. In practice, this often leads to excessively high flows from the point emitters with negative impact on the soil. The rate at which water enters dry soil and the ability of a soil to conduct or transmit water determine the soil–water distribution patterns. Such patterns, however, can be modified by changing the rate and frequency of water application. Although water rates through the point systems are considered low, a puddle around the emitter can occur under field conditions when the discharge rate of emitter exceeds the ability of the soil to absorb the water. In such cases the horizontal movement of water increases as the puddle area increases in size. When water is applied in such a way that the puddle is minimal, soil aeration would be adequate because the soil will come near saturation only around the water source. Point irrigation systems must be designed to meet the crop water requirements while applying water at a rate no more than the soil can accept. As the rate of infiltration of soils typically decreases with time, the longer the point system is operated the greater the potential for creating puddles and subsequent run-off. In soils of very low infiltration rates, puddles can be avoided only by cycling the system at frequent intervals (pulse irrigation) within the duration of irrigation. To maintain high levels of water in the wetted zone and to avoid puddles and run-off, point irrigation systems should be operated as frequently as possible.

Water application through the point delivery system is based on moisture movement in a small area of the soil. To evaluate the effectiveness of a point source irrigation system, the wetted area, wetting pattern and vertical as well as horizontal water movement in the soil should be measured (Trickle irrigation, 1984). Field experiments are needed to evaluate the assumption of homogeneity, or to determine the largest units that can still be assumed homogeneous to enable modeling. To evaluate the generic design values for point source irrigation, field and laboratory experiments can be conducted and evaluated (Brandt et al., 1971). Although the statement obtained from the USDA-SCS National Engineering Handbook (1984) is true, research is trying to obtain knowledge on what variables affect the movement of water in the soil under point source irrigation, to enable more generic irrigation design values. The authors provide several relationships based on experimental work, applicable under the conditions that they had been developed for (yet generalizing for the heterogeneity of the soil and field conditions). Clothier et al. (1985) show that in some cases the hydraulic properties of soil can be so variable in time and space as to negate the utility of detailed theoretical analyses. Until reliable and easier mathematical methods have been developed, it is suggested that field experiments or empirical methods be used. The objective of the present work is to develop a guide for determining the geometry of the wetted soil volume under irrigation point sources. Furthermore, the experimental results obtained will help in testing the validity of mathematical models of infiltration from a point source.

Section snippets

Materials and methods

The field experiments using different emitter discharges and various periods of irrigation on haplic Luvisol (ha LV) (ALFISOLS Udalfs) on loess were conducted in order to determine horizontal and vertical water movements in a soil profile.

The initial design application volume was calculated using the required wetted soil volume, based on the root zone depth and the emitter spacing, and the available soil water storage, based on the initial soil water content and the theoretically maximum soil

Results

A method for determining the width and depth of the wetted soil volume under the point irrigation was developed.

The water content distribution data obtained from the field experiments carried out in haplic Luvisol (ha LV) on loess were compared with the experimental results of other authors in order to establish their reliability.

Using the dependence of r = f (Q) and rFC = f (Q) as shown in Fig. 5, Fig. 6 it has been determined that the average maximum distance of horizontal expansion of soil

Discussion

Results of our research were compared with those obtained by other authors. None of these authors had measured the values of field water capacity (ΘFC). They focused only on establishing the locations of the wetting fronts, i.e. the dimensions of the volume of moistened soil. We could therefore compare only the dimensions of the moistened soil volumes. Furthermore, most published papers described only the type of the soil being studied without any details of its characteristics.

Other research

Conclusions

On the basis of the field experiments on haplic Luvisol (ha LV) (ALFISOLS Udalfs) on loess we have determined that point irrigation is most effective when it does not exceed the available soil water storage Q (l). If the maximum water rate Qmax (l) exceeds QFC (l), then any excess water passes through the plants root zone and it is lost.

Furthermore, the excess water also percolates below the 1 m depth of the soil and washes out the fine soil particles which are also permanently lost from the

Acknowledgements

The authors gratefully thank the anonymous reviewers for their peer reviews and contributions on the quality of the paper. The authors also thank Professor Jaroslav Voracek of the CULS Prague for his considerable help in reviewing the English version of this paper. A grant from the Czech Ministry of Agriculture, Project No. QH 92086 supported this research.

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