Creating and Consolidating Locally Managed Irrigation in Turkey: the National Perspective

The Turkish program of irrigationmanagement transfer has gained worldwidecelebrity for its speed and effectiveness. This paper describes the program brieflyand assesses its effectiveness from anational perspective. The assessmentincludes changes in staffing levels,operational costs, service fee levels, andcost recovery from farmers. A companionpaper examines impacts at the local leveland looks specifically at changes in systemperformance.     

Economic and agronomic strategies to achieve sustainable irrigation

The achievement of sustainable irrigation in arid regions requires greater attention to waterlogging, salinization, and degradation of ground and surface waters, which are among the problems that continue to threaten productivity and degrade environmental quality. We consider sustainability to be achieved when irrigation and drainage are conducted on-farm, and within irrigation districts, in a manner that does not degrade the quality of land, water, and other natural resources, either on-farm or throughout an irrigated region. Sustainability may also be described as maintaining the productive resources required for irrigation, so that future generations may have the same opportunity to use those resources as we do. Given the increasing importance of irrigated land for food production, the time has come when it is vital to intercept, reuse, and isolate drainage waters within the regions in which they are generated. Adoption of this strategy can be enhanced by policies that require farmers, and irrigation districts, to consider the off-farm impacts of irrigation and drainage. Such policies include linking water rights with salt rights to require the monitoring and management of both irrigation water and the salt loads in drainage waters. We review the knowledge gained since the early 1970s regarding the economic and agronomic aspects of irrigation and drainage, with a focus on drainage water reduction and sequential reuse of drainage water on salt-tolerant crops. Economic incentives that motivate farm-level and district-level improvements in water management are also reviewed. We conclude that adequate knowledge exists for implementing strategies that focus on water use and salt disposal within irrigated regions, and we recommend policies that will motivate improvements in productivity and enhance the likelihood of achieving sustainability.     

Effect of drying on soil strength and corn emergence

Summary Laboratory studies were conducted to evaluate the effects of drying on soil strength and corn emergence (Zea mays L.). Corn was germinated in Billings silty clay under a bank of heat lamps which operated 9, 14, 19, or 24 h per day. Soil strength (modules of rupture), soil moisture content and emergence were measured daily.The relationship of soil strength to corn seedling emergence as influenced by the four light and heat durations and bare and mulched soil surfaces was determined. As soil strength increased emergence decreased until it ceased at soil strengths of about 80 kPa. Strength of this soil had a high negative correlation with soil water content and increased with time. Mulching decreased initial rate of drying, decreased crust strength, and improved corn emergence. The 14-hour light and heat treatment resulted in the highest corn emergence.Contribution from Colorado State Experiment Station, USDA-ARS Snake River Conservation Research Center, and USDA-ARS Fort Collins, respectively     

Role of transpiration suppression by evaporation of intercepted water in improving irrigation efficiency

Sprinkler irrigation efficiency declines when applied water intercepted by the crop foliage, or gross interception (I_gross), as well as airborne droplets and ponded water at the soil surface evaporate before use by the crop. However, evaporation of applied water can also supply some of the atmospheric demands usually met by plant transpiration. Any suppression of crop transpiration from the irrigated area as compared to a non-irrigated area can be subtracted from I_gross irrigation application losses for a reduced, or net, interception (I_net) loss. This study was conducted to determine the extent in which transpiration suppression due to microclimatic modification resulting from evaporation of plant-intercepted water and/or of applied water can reduce total sprinkler irrigation application losses of impact sprinkler and low energy precision application (LEPA) irrigation systems. Fully irrigated corn (Zea Mays L.) was grown on 0.75 m wide east-west rows in 1990 at Bushland, TX in two contiguous 5-ha fields, each containing a weighing lysimeter and micrometeorological instrumentation. Transpiration (Tr) was measured using heat balance sap flow gauges. During and following an impact sprinkler irrigation, within-canopy vapor pressure deficit and canopy temperature declined sharply due to canopyintercepted water and microclimatic modification from evaporation. For an average day time impact irrigation application of 21 mm, estimated average I_gross loss was 10.7%, but the resulting suppression of measured Tr by 50% or more during the irrigation reduced I_gross loss by 3.9%. On days of high solar radiation, continued transpiration suppression following the irrigation reduced I_gross loss an additional 1.2%. Further 4–6% reductions in I_gross losses were predicted when aerodynamic and canopy resistances were considered. Irrigation water applied only at the soil surface by LEPA irrigation had little effect on the microclimate within the canopy and consequently on Tr or ET, or irrigation application efficiency.     

Simulated water and solute distribution from a crossed triple line-source

Summary Multivariable irrigation experiments are usually expensive and seldom cover the whole range of desired values. The crossed triple line-source (CTLS) was designed to provide a relatively simple and inexpensive irrigation system for creating continuous gradients of more than one variable. A computer model was developed to assist in evaluating the continuously changing multivariable levels, produced by the CTLS, given various inputs. A single sprinkler's distribution function was used in the model's development. The results of the overlapping sprinkling patterns are calculated throughout the experimental area for water depth, salinity level, and Nitrogen concentration. Measured values of irrigation water electrical conductivity (EC_i) and Nitrogen concentration were in good agreement with predicted values.     

Effect of soil matric potential,method of irrigation and nitrogen fertilization on yield,quality, nutrient uptake and water use of radish (Raphanus sativus L.)

Summary Field experiments carried out at the Indian Institute of Horticultural Research, Bangalore during 1983 and 1984 on radish indicated that frequent irrigations when soil matric potential reached –20 kPa at 18 cm depth resulted in maximum root yield, lower NO₃-N content in roots, higher N, P, K, Ca and WUE of radish.Contribution No. 63/86 from Indian Institute of Horticultural Research, Bangalore, India     

Roots in irrigated clay soils: Measurement techniques and responses to rootzone conditions

Summary This paper reviews research carried out at the Griffith Laboratory in Australia over the last decade on techniques for, and results of, observations of roots in irrigated clay soils. Our results emphasise the adaptability of root systems to rootzone conditions. Experiences with techniques for observing roots non-destructively in the field and both non-destructively and destructively in lysimeters are described. We concluded that the minirhizotron technique, applied in the field, was unreliable under our conditions. Horizontal root observation tubes were used in lysimeters to measure root length density (RLD) and to assess whether roots were clumped together or randomly distributed. Destructive sampling and measurement of RLD was used to establish a theoretical relationship between root intercept counts along the tubes and RLD. The application of image analysis to both destructive and non-destructive sampling in the lysimeters is outlined. The non-destructive lysimeter studies showed that roots were significantly clumped. Analysis of root intercept and root hole counts on the faces of sample cubes taken from the lysimeters showed root distribution was anisotropic over the whole soil profile for both safflower and wheat. There were many more roots and root holes present in the sampled soil cubes than was indicated by independent sampling for washed out RLD. Safflower appeared to have a faster turnover of roots than did wheat or maize. Lysimeters, equipped with horizontal root observation tubes, enabled studies to be made of many factors affecting root growth. Soils affect where and how fast roots grow, although there is also a strong species interaction. For example, soybean roots proliferated above a fresh water table in one soil but not in another; wheat had little tendency to proliferate above the water table in either soil. In wet soils, roots cease to grow once soil oxygen levels decrease below 10 mg O₂ l _soil ^-1 . This level should form the basis for soil drainage criteria. In drying soils, roots will grow successively into soil regions containing soil water: the level of adaptation being determined by soil conditions, crop growth stage and level of evaporative demand. The methods of root observation used in our studies have given quantitative assessment of root distribution. However, further research is needed to link horizontal and vertical root distribution and root adaptation more strongly to crop development and soil conditions.     

Effects of soil type on soybean crop water use in weighing lysimeters

Summary Different soils are known to affect the amount and distribution of both available water and roots. Optimising irrigation water use, especially when shallow water-tables are present requires accurate knowledge of the root zone dynamics. This study was conducted to determine the effect of two soil types on root growth, soil water extraction patterns, and contributions of a water-table to crop evaporation (E). Two weighing lysimeters (L1 and L2) with undisturbed blocks of soil were used. The soil in L1 had higher hydraulic conductivity and lower bulk density than that in L2. Well watered conditions were maintained by irrigation for the first 110 days from sowing (DFS). Root length density (RLD) was calculated from observations made in clear acrylic tubes installed into the sides of the lysimeters. Volumetric soil water contents were measured with a neutron probe. A water-table (EC = 0.01 S m^-1) was established 1 m below the soil surface 18 DFS. RLD values were greater in L1 than L2 at any depth. In L1, maximum RLD values (3 × 10⁴ m m^-3) were measured immediately above the water-table at physiological maturity (133 DFS). In L2, maximum RLD values (1.5 × 10⁴ m m^-3) were measured at 0.42 m on 120 DFS and few roots were present above the water-table. From 71 to 74 DFS, 55 and 64% of E was extracted from above 0.2 m for L1 and L2, respectively. In L2, extraction was essentially limited to the upper 0.4 m, while L1 extraction was to 0.8 m depth. Around 100 DFS the water-table contributed 29% (L1) and 7% (L2) of the water evaporated. This proportion increased rapidly as the upper soil layers dried following the last substantial irrigation 106 DFS. Over the whole season the water-table contributed 24% in L1 and 6.5% in L2 of total E.     

Infiltration parameters from optimisation on furrow irrigation advance data

Knowledge of the soil infiltration parameters is necessary for efficient furrow irrigation. A method is proposed for the determination of the parameters in the Kostiakov-Lewis infiltration equation from measurements of the furrow irrigation advance and inflow. The method employs a volume balance model using optimisation to minimise the error between the predicted and measured advance and differs from existing approaches in that only advance data and inflow rates are required. The average cross sectional area of the furrow and the final infiltration rate are treated as fitted parameters and need not be measured. A simple but effective optimisation algorithm is developed which allows for the solution of the four parameters without user input. The speed and simplicity of the optimisation may lead to application in real-time control of furrow irrigation. Received: 16 August 1995