Determination of Soil Water Retention Curve

The water retention function 6 (h) usually is determined in the laboratory on undisturbed soil cores by proceeding through a series of wetting and drainage events and taking measurements at equilibrium conditions, or in the field by measuring simultaneously water contents and pressure potentials during a transient flow experiment. Reviews of direct methods for determining the soil water-retention curve can be found in the literature for laboratory analyses on soil cores 14 and for field soils...

Classification of Rural Roads

Roads can be categorized in many different ways. In relationship to Fig. 3.2, a classification may be based on road design (construction), use (traffic characteristics), or function. For planning purposes, a classification by function is most useful. This is elaborated in the next sections, for both industrialized and developing countries. Classifications by road design are commonly based on pavement width and type. The distinction paved unpaved is the simplest classification. Road surfaces can...

Yield Salinity Relationships

Many arid or semiarid soils contain concentrations of soluble salts that have a negative impact on the efficiency of water use. In irrigated agriculture, salinity is probably the second most important yield constraint to irrigation. In addition to a direct osmotic effect and a possible toxicity of specific ions, soil salinity and salts present in the irrigation water may have a deleterious impact on physical properties such as infiltrabil-ity, water holding, and aeration, especially if the soil...

Construction

Construction of the road body will depend on the subsoil (bearing characteristics, uniformity), environmental conditions (hydrological conditions, frost), traffic (frequency of standard single-axle weight), and construction materials (toughness, stability). Whereas proven standard values should govern the construction of dirt roads and rigid-type roads (concrete slabs), the following should conform more to a flexible construction style. In Table 3.9. Type of road and traffic volume Frequency of...

Water Use Efficiency WUE

The term transpiration ratio (TR) was introduced 33 to quantify the relation between crop transpiration and crop dry-matter production. TR is defined as the mass ratio of crop transpiration to crop dry-matter production. This term was later called the transpiration coefficient. The TR concept has been expanded and improved by normalizing the transpiration by the mean daily potential evaporation during the growing season 34 . The analysis of photosynthesis and transpiration based on physiology...

Set Sprinkler Systems

Set systems, using many small rotary sprinklers operating together, are the most commonly used sprinkler system. The sprinklers operate at medium to high pressures. Application rates vary from 3 to 35 mm h-1. Single laterals can irrigate an area 9 to 24 m wide and up to 400 m long at one setting. Set systems are described in detail by several authors 11,94-99 . When sufficient laterals and sprinklers are provided to cover the whole irrigated area so that no equipment needs to be moved, the...

Kc Kcb Ke554

Where Kcb + Ke represents the sum of the basal Kcb and time-averaged effects of evaporation from the surface soil layer, Ke. Typical shapes for the Kcb, Ke, and Kcb + Ke curves are shown in Fig. 5.4. The Kcb curve in the figure represents the minimum Kc for conditions of adequate soil moisture and dry soil surface. The Ke spikes in the figure represent increased evaporation when precipitation or irrigation has wetted the soil surface and has temporarily increased total ETc. The spikes generally...

Issues on Irrigation Performance

The distribution uniformity DU Eq. (5.119) is determined by several design variables and can be expressed functionally by the following relation DU f (P, AP, S, dn, WDP, WS), (5.148) where P is the pressure (kPa) available at the sprinkler, A P is the variation of the pressure (kPa) in the operating set or along the moving lateral, S represents the spacings (m) of the sprinklers along the lateral and between laterals or spacings between travelers, dn is the nozzle diameter (mm), which...

System Layout and Components

Basic components of a microirrigation system are the pump, filtration equipment, controllers, main pressure regulators, control valves, water-measuring devices, and chemical injection equipment, which usually are centrally located at the pump filtration station the delivery system, including the main and submain pipelines that transfer water from Very sensitive Sensitive Low sensitive Extremely sensitive filters < 80 xm Very sensitive filters 80 xm Low sensitive filters 125 xm Very low...

Access to Inputs and Services

The access to inputs and services determines to a large degree the possibilities of agricultural development in a country or area. With good access to, for example, cheap fertilizers, good seeds, bank credit, and the results of agricultural research, a farmer has a greater chance of increasing the farm's profitability. A good example is the Green Revolution in Asia. When farmers in that part of the world got access to high-yield varieties of rice and wheat, the production of these crops...

Mediterranean Agriculture

Mediterranean agriculture is found in the areas surrounding the Mediterranean Sea and in areas with a similar climate, characterized by mild, wet winters and hot, dry summers 5 . There are four land-use patterns that characterize the traditional Mediterranean farming system 5 extensive wheat cultivation extensive grazing by sheep and goats cultivation of tree crops such as olives and figs, grapes, and date palms cultivation of fruits and vegetables, with apples, peaches, and pears as most...

Soil Heat Flux Density G

For daily calculations, G (MJ m-2 day-1) can be estimated using a simplified approach to the heat balance of the soil profile where T is the mean daily air temperature ( C), T-1 is the mean air temperature ( C) of the preceding three-day period, and 0.1 is an empirical conversion factor (MJ m-2 day-1 C-1). Because the magnitude of daily soil heat flux beneath densely planted grass is relatively small, it can be neglected (i.e., G 0). For monthly time-step calculations, G can be computed from...

Description ofSystems

The practice of surface irrigation is ancient and is used on more than 90 of the world's irrigated area. The sustainability of irrigated agriculture depends on improvements and innovations in surface irrigation methods, their appropriateness for the different systems, and their adoption in field practice. Surface irrigation methods include several processes of water application to irrigated fields 16 furrow, basin, border, contour ditches (wild flooding), and water spreading. The two last...

Average Crop Coefficients

A simple procedure is used to construct the Kc curve for the complete growing period. This procedure was first presented by Doorenbos and Pruitt 55 . The Kc curve, such as that shown in Fig. 5.5, is constructed using the following three steps 1. Divide the growing period into four general growth stages that describe crop phenology or development, and determine the lengths of these stages, in days. The four stages are initial period, crop development period, midseason period, late-season period....

Other Types of Road Construction

Roads with continuous pavement are much appreciated for such leisure activities as bicycling, jogging, or rollerskating, although avoided by other users such as ramblers. In vulnerable areas, objections often are raised to pavement for reasons that have to do with the landscape. Many spur roads are built in such areas, a variation that has proven its worth. The tracks for vehicles usually are made of concrete, with grass in between Figure 3.15. Nomogram for the construction of roads with low...

Moving Lateral Systems

These systems have laterals that move continuously while applying water. There are three main types of systems center pivot, lateral move, and side move (for complementary information see 11, 94-96, 99 ). These systems consist of a single galvanized steel lateral that rotates in a circle about a fixed pivot point in the center of the field (Fig. 5.27). Lateral pipe diameters range from 100 to 250 mm. The lateral is supported using cables or trusses as much as 3 m above the ground on A-shaped...

Substratum and Foundation

The optimum requirements will have been met if the subsoil has excellent bearing capacity and also can be used as building material, which can reduce the construction costs drastically. Unfortunately, such conditions are rare. Most sites either have been developed already or lack the appropriate dimensions. Geology is differentiated only Figure 3.12. Standard cross section of a minor rural road. Source Adapted from 23 . Figure 3.12. Standard cross section of a minor rural road. Source Adapted...

Planning for the Opening Up of Developing Rural Areas

Today, planning issues regarding the opening up of areas that are solely agricultural are confined mainly to developing countries. Especially in these countries remoteness, isolation, and inaccessibility are key characteristics. Moreover, the economic and social deprivation that these areas suffer is often largely due to inadequate transportation services. Investment in transport facilities is usually just one element of an integrated development program. This is designed to improve standards...

Sprinklers

Sprinkler heads are the most important component in the system because their performance determines the effectiveness and efficiency of the whole system. A sprinkler operates by forcing water under pressure through a small hole or nozzle and into the air. Nozzle size and water pressure determine the flow rate. Most sprinklers are designed to give a circular wetting pattern. The distance from the sprinkler to the outer edge of that circle is called the throw or wetted radius. Nozzle design,...

Field Evaluation

Field evaluation of sprinkler systems in operation can play a major role in improving irrigation performance. Field evaluations of set systems include the following observations 10, 11, 19, 110 pressure at the sprinkler nozzles at different locations pressure variation A P along a lateral and within the operating set sprinkler discharges and respective variations along a lateral and within the operating set applied depths in a sample area on both sides of a lateral or between two laterals...

Planning for the Opening Up of Agricultural Areas

Several studies are available on so-called optimal agricultural field length. Boss and Flury 4 cite a Swiss study from the early 1980s. This study shows that fields suitable for arable farming require a road on both sides, whereas one road is sufficient for grassland. Figure 3.7. Optimum field lengths for a 16-ha farm with several crop cultivations. Source 4 , reprinted by permission of PUDOC-DLO, Wageningen. Figure 3.7. Optimum field lengths for a 16-ha farm with several crop cultivations....

Preface and Acknowledgments

Land and Water Engineering are becoming increasingly important globally for the future of humankind. There are at least two main reasons for this growing significance First, it is well understood that, aside from several other means, the wise use of land and water will play a key role in the provision of enough good food for future generations. Despite all types ofprograms and policies, the global population still increases and most probably will continue to do so for the next half century or...

Definition of Reference Evapotranspiration

The primary purpose for developing ET0 equations is to estimate a reference ET by which a crop coefficient is multiplied to obtain an estimate of crop ET. In many instances, the ET0 equation has represented a hypothetical living crop reference in order to provide for a complete record of ET0 during the development of crop coefficients and during calibration or analysis of other ET equations. Wright and Jensen 53 and Wright 71 utilized a hypothetical alfalfa ET0 Jensen 54 and Jensen et al. 2...

Yield Irrigation Depth Relationships

Irrigation is the primary management practice that is utilized to increase crop yields (or to permit crop production) in semiarid and arid climates. In addition, irrigation is used to stabilize crop yields when rainfall is unreliable in subhumid and humid climates. Including irrigation depths (IR) in the ratios of DM production or marketable yield (Y) to transpiration (T) or evapotranspiration (ET) is necessary when making both engineering and economic decisions, to determine the optimal...

General Aspects

Microirrigation, also called trickle or drip irrigation, applies water to individual plants or small groups of plants. Application rates are usually low to avoid water ponding and minimize the size of distribution tubing. The microirrigation systems in common use today can be classified in two general categories Drip irrigation, by which water is applied slowly through small emitter openings from plastic tubing. Drip tubing and emitters may be laid on the soil surface, buried, or suspended from...

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Cablegation Irrigation

Appropriate control of inflow rates and duration of irrigation is particularly relevant where overirrigation has to be avoided. This is the case when deep percolation of excess water contributes to water table rise, salinization, leaching of fertilizers and other agrochemicals, and excessive drainage volumes. Such control is also essential when irrigating saline soils or using saline water. Therefore, the improved control of qin and co becomes not only a matter of irrigation performance but...

Irrigation Management Under Water Shortage Conditions

The lack of water has a negative effect on the whole set of vital plant processes such as photosynthesis, respiration, absorption of nutrients, and assimilate translocation. It also affects growth, reproduction, and the development of the seed. From the agronomical point of view, the main interest is focused on the effect of water deficit on yield. The effect of water stress on plant development and productivity has been the object of several studies 32-35 and is dealt with in Section 5.5. The...

References

Updated evapotranspiration and crop water requirement definitions. Crop Water Requirements, eds. Perrier, A., and C. Riou, pp. 885-887. Paris INRA. 2. Jensen, M. E., R. D. Burman, and R. G. Allen (eds.). 1990. Evapotranspiration and Irrigation Water Requirements. ASCE Manuals and Reports on Engineering Practices No. 70, New York. 3. Doorenbos, J., and W. O. Pruitt. 1975. Guidelines for Predicting Crop Water Requirements, FAO Irrigation and Drainage Paper 24, Rome FAO. 4....

Mobile Raingun Systems

Mobile raingun systems (also called traveling sprinklers or travelers) use a large rotary sprinkler operating at high pressure. The term raingun is used because of the large size of sprinkler used and its ability to throw large quantities of water over wide areas. They have become popular because of their relatively low capital cost and low labor requirements. They are well adapted to supplemental irrigation. Because of the high pressure requirements, they have high energy costs. Rainguns...

Soil Water Potential

Water present in an unsaturated porous medium such as soil is subject to a variety of forces acting in different directions. The terrestrial gravitational field and the overburden loads due to the weight of soil layers overlying a nonrigid porous system tend to move the soil water in the vertical direction. The attractive forces occurring between the polar water molecules and the surface of the solid matrix and those coming into play at the separation interface between the liquid and gaseous...

Reclamation Procedures

Methods of reclamation have to be tailored to the specific problems at hand. However, there are some principles that are common to all reclamation procedures. Figure 4.7 shows the steps and the considerations that are necessary in the design of a suitable reclamation scheme. We have to bring back to full life an ecosystem in which normal biological processes are at a standstill. The natural development of such an ecosystem normally takes a long time, and so, the key to improvement is upgrading...

Balancing Agriculture Between Development and Conservation

Increasing agricultural production has always been the main goal of agricultural research. Because of the continuing growth of the world's population and the important share of agricultural products in the world economy, this increase of agricultural production will continue to be important, but under different conditions. The more or less uncontrolled growth in agricultural production during the past few decades, in industrial as well as developing countries, has pushed agricultural production...

Measurement of Soil Losses from Erosion

Soil Erosion Stages

The characteristics of the experimental site are determined by the experimental objectives and the type of data to be obtained. Generally, plots are used to study physical phenomena affecting soil detachment and transport whereas complex hill slopes or small watersheds are gauged for examining deposition processes and therefore sediment yield. In an experimental station for soil erosion studies, bounded runoff plots of known width, slope length, slope steepness, and soil type are monitored....

Case When Wind Speed Data Are Missing

Two approaches can be utilized to overcome the problem of missing windspeed data. Use of Wind-Speed Data from a Nearby Weather Station. Importing wind-speed data from a nearby station, as for Rs discussed earlier, relies on the fact that airflow above a homogeneous region may have relatively large space variations during the course of a day but small variation over longer periods or even over the day itself. This occurs when air masses are of the same origin or when the same fronts govern...

The Penman Monteith ET0 Equation

The grass reference crop in the above definition can be fully described using the PM approach. The grass reference crop is probably, together with alfalfa, the best-studied crop regarding its aerodynamic and bulk stomatal characteristics 2, 21, 59, 60 . The aerodynamic resistance ra (Eq. 5.4) can be calculated easily because the zero plane displacement height can be estimated from the crop height h, d 0.67h the roughness height for momentum transfer can be given by zom 0.123h and the roughness...

Crop Water Models

Agricultural planning is a wide management field 88 . Irrigation management consists of determining when to irrigate, the amount to apply at each irrigation and during each stage of plant growth, and the operation and maintenance of the irrigation system. The primary objective is to manage the production system for profit without compromising the environment. The major management activity involves irrigation scheduling. Most irrigation water management concepts include salinity control and the...

Stabilizing Structures for Gullies and Embankments

The mechanics of gully erosion can be reduced to two main processes 24 down-cutting and headcutting. Downcutting of the gully bottom leads to gully deepening and widening. Headcutting extends the channel into ungullied headwater areas and increases the stream net and its density by developing tributaries. Thus, effective gully control must stabilize both the channel gradient and the channel headcuts. Where an effective vegetation cover will grow, gradients can be controlled by the establishment...

Measurement of Water Content of Soil

The measurement of water content in the soil is of great importance in many investigations and applications pertaining to agriculture, hydrology, meteorology, hydraulic engineering, and soil mechanics. In the fields of agronomy and forestry, the amount of water contained in the soil affects plant growth and diffusion of nutrients toward the plant roots, as well as acting on soil aeration and gaseous exchanges, with direct consequences for root respiration. Also, continuous monitoring of soil...

Measurement of Soil Water Potential

Knowing soil water potential values in soil is of primary importance in studies of transport processes within porous media as well as in evaluating the energy status of water in the crops. The most widely known direct method for measuring the pressure potential in soil is that associated with use of a tensiometer 2 . The matric potential then can be calculated from measurements of the gas-phase pressure, if different from the atmospheric pressure, and of the overburden potentials in the case of...

Salty Soils Problems

Salts occur in the soil in one of the following three forms salt ions dissolved in the soil water the soil solution , cations adsorbed on the negatively charged surfaces of the soil particles adsorption complex , and precipitated salts. The principal salts are sodium, magnesium, and calcium chlorides sodium and magnesium sulfates sodium carbonates and bicarbonates and nitrates and borates. These originate from rocks as they weather into soil. In this process the salts are carried downward...

Types of Erosion and Its Assessment

Soil is a vital resource for the production of renewable resources for the necessities of human life, such as food and fiber. Soils, however, essentially are nonrenewable resources 1 . According to Golubev 2 , the area of cultivated land in the world is 14.3 million km2. In cultivated areas, drastic changes in vegetation have occurred and instead of dense natural vegetation cover, bare soil often is exposed for most of the year with sparse crop vegetation existing for a few months. These...