Analysis of trickle irrigation with application to design problems

Summary Designing trickle irrigation systems involves the selection of a proper combination of trickle discharge rate, spacing between emitters, diameter and length of the lateral system for any given set of soil, crop and climatic conditions. Trickle irrigation is treated as transient and steady axisymmetric infiltration processes. An existing numerical solution to nonsteady state infiltration is used to quantify the effect of soil hydraulic properties and trickle discharge rates on emitter spacing (Fig. 2). The results of the analysis suggest the possibility of controlling the wetted volume of a soil by regulating the emitter discharge according to soil properties (Figs. 3 and 4). The surface distribution of a transformed soil water content (or pressure) function (Fig. 5) is derived from a linearized solution to steady infiltration. The analysis of steady and non-steady infiltration is employed to estimate the spacing between emitters as a function of discharge and water pressure conditions between emitters using hydraulic soil data (Fig. 6). Hydraulic conductivity parameters are given for 17 different soils (Table 1) to be used for design purposes. Theoretical analysis of soil water is combined with hydraulic principles to derive lateral diameter and length for engineering design requirements.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. 1977 Series, No. 134-E     

Long-term growth and yield responses of olive trees to different irrigation regimes

The aim of this work was to evaluate long-term effects of different irrigation regimes on mature olive trees growing under field conditions. A 9-year experiment was carried out. Three irrigation treatments were applied: no irrigation, water application considering soil water content (short irrigation), or irrigation without considering soil water reserves and applying a 20% of extra water as a leaching fraction (long irrigation). Leaf water content, leaf area, vegetative growth, yield and fruit characteristics (fruit size, pulp:stone ratio and oil content) were determined yearly. Results showed that growth parameters did not show significant differences as a consequence of applied water. Yield was increased in irrigated trees compared to non-irrigated ones, but little differences between short and long irrigation were observed, only when accumulated yield from 1998 to 2006 was considered. Irrigation did not cause significant differences in fruit size or pulp:stone ratio either. Irrigation regimes similar to those applied in this experiment, under environmental conditions with relatively high mean annual precipitation, does not increase growth, yield or fruit characteristics when compared to rain-fed treatment, and consequently, the installation of a irrigation system could be not financially profitable.     

The fate of nitrogen applied to sugarcane by trickle irrigation

Fertigation can be a more efficient means of applying crop nutrients, particularly nitrogen (N), so that nutrient application rates can be reduced in fertigated crops. However, there is little information on the extent of the possible reduction in N application rate for fertigated sugarcane, one of the major row crops grown under trickle irrigation, nor the fate of N in fertigated sugarcane systems if N application rates are not reduced. An experiment was established to determine the response of cane and sugar production to different N rates (0–240 kg ha^–1 year^–1) spanning that recommended for conventional irrigation systems (160 kg ha^–1 year^–1). As well as yield, N removed in the crop and changes in soil mineral N were determined annually for four crops (a plant and three ratoon crops). ¹⁵N values were also measured in selected treatments at selected times to assess possible N inputs to the experiment via biological N fixation (BFN). Yields of cane and sugar responded to application of N fertiliser in the three ratoon crops, but they were not significantly increased by applying more than 80 kg ha^–1 of N. There were no N responses in the plant crop, as there was >200 kg ha^–1 of soil mineral N (SMN) to 2 m depth at the site prior to planting, and much of this SMN was depleted in the treatment receiving no N. There was no evidence of N input from BFN in the experiment. During the 4-year study period, net removal of N from the treatment with no applied N totalled 207 kg ha^–1. When 80 or 120 kg ha^–1 year^–1 of N was applied to ratoon crops, outputs of N from the harvested crop approximately balanced inputs from fertiliser and depletion of SMN during the experiment. Inputs clearly exceeded output at higher N application rates. Assuming that the net removal of N from the treatment with no applied N was the same as the net mineralisation of N from soil organic matter in all treatments in the experiment, 204–639 kg ha^–1 of N was unaccounted for in the treatments with applied N over the duration of the experiment. While some of this N (e.g. 45 kg ha^–1) may have resulted in small (and undetectable) increases in total soil N, much of it would have been lost to the environment. We suggest that the high soil water contents maintained with daily application of irrigation water through the trickle system promotes mineralisation of soil organic matter and hence losses of N to the environment. Thus, particular care is required to avoid over-application of N in fertigated sugarcane.Communicated by K. Bristow     

Corn yield responses under crop evapotranspiration-based irrigation management

Improving irrigation water management is becoming important to produce a profitable crop in South Texas as the water supplies shrink. This study was conducted to investigate grain yield responses of corn (Zea mays) under irrigation management based on crop evapotranspiration (ET_C) as well as a possibility to monitor plant water deficiencies using some of physiological and environmental factors. Three commercial corn cultivars were grown in a center-pivot-irrigated field with low energy precision application (LEPA) at Texas AgriLife Research Center in Uvalde, TX from 2002 to 2004. The field was treated with conventional and reduced tillage practices and irrigation regimes of 100%, 75%, and 50% ET_C. Grain yield was increased as irrigation increased. There were significant differences between 100% and 50% ET_C in volumetric water content (θ), leaf relative water content (RWC), and canopy temperature (T_C). It is considered that irrigation management of corn at 75% ET_C is feasible with 10% reduction of grain yield and with increased water use efficiency (WUE). The greatest WUE (1.6 g m⁻² mm⁻¹) achieved at 456 mm of water input while grain yield plateaued at less than 600 mm. The result demonstrates that ET_C-based irrigation can be one of the efficient water delivery schemes. The results also demonstrate that grain yield reduction of corn is qualitatively describable using the variables of RWC and T_C. Therefore, it appears that water status can be monitored with measurement of the variables, promising future development of real-time irrigation scheduling.     

Response of cotton to treated domestic wastewater applied through trickle irrigation

Summary Field experiments were conducted under arid zone conditions to examine cotton response to treated domestic wastewater applied at different frequencies and emitter spacings by trickle irrigation.Row spacing was either conventional, i.e. single rows apart, or in twin rows, 0.96 m and 1.92 m apart (a twin row consists of a pair 0.35 m apart). Some treatments received the commercial rates of effluent application (around 5,500 m³/ha) as commonly practiced in the area, others received a reduced amount, 80% of the commercial rate.Maximum yield (over 7,000 kg/ha) was obtained under twin row planting, irrigated twice a week with a commercial amount of effluent. A yield of 6,040 kg/ha was obtained under twin row planting irrigated once a week or each day. Under conventional row and emitter spacing, irrigated twice a week, the yield was 6.016 kg/ha.     

LEPA and trickle irrigation of cotton in the Southeast Anatolia Project (GAP) area in Turkey

This study was designed to evaluate the yield response of low-energy precision application (LEPA) and trickle-irrigated cotton grown on a clay-textured soil under the arid Southeast Anatolia Project (GAP) area conditions during the 1999 growing season at Koruklu in Turkey. The effects of four different irrigation levels (100, 75, 50, and 25% of cumulative Class-A pan evaporation on a 6-day basis) for LEPA, and two irrigation intervals (3-day and 6-day) and three different levels (100, 67, and 33% of cumulative Class-A pan evaporation on a 3-day and 6-day basis) for the trickle system on yield were investigated. Water was applied to alternate furrows through the double-ended Fangmeier drag-socks in the LEPA system. Trickle irrigation laterals were laid out on the soil surface at a spacing of 1.40 m. A total of 814 mm of water was applied to the full-irrigation treatments (100%) for both irrigation systems. Seasonal water use ranged from 383 to 854 mm in LEPA treatments; and 456 to 868 mm in trickle treatments. Highest average cotton yield of 5850 kg/ha was obtained from the full-irrigation treatment (100%) in trickle-irrigated plots with 6-day intervals. The highest yield in LEPA plots was obtained in LEPA-100% treatment with an average value of 4750 kg/ha. Seed cotton yields varied from 2660 to 5040 kg/ha and 2310 to 5850 kg/ha in trickle irrigation plots with 3-day and 6-day intervals, respectively, and from 2590 to 4750 kg/ha in LEPA plots. Irrigation levels both in LEPA and trickle-irrigated plots significantly increased yield. However, there was no significant yield difference between 100 and 67% irrigation levels in trickle-irrigated plots. Maximum irrigation water use efficiency (IWUE) and water use efficiency (WUE) were found as 0.813 and 0.741 kg/m³ in trickle-irrigated treatment of 67% with 6-day interval. Both IWUE and WUE values varied with irrigation quantity and frequency. The research results revealed that both the trickle and LEPA irrigation systems could be used successfully for irrigating cotton crop under the arid climatic conditions of the GAP area in Turkey.     

Plant growth and yield responses in olive (Olea europaea) to different irrigation levels in an arid region of Argentina

Over the last two decades, a significant increase in intensively managed olive orchards has occurred in the northwest of Argentina where climatic conditions differ greatly from the Mediterranean Basin. Annual amounts of applied irrigation are generally high due to low rainfall, access to deep ground water, and little information about water use by the crop in the region. The objectives of this study were to: (1) assess the responses of plant growth, yield components, and several physiological parameters to five different irrigation levels and (2) determine an optimum crop coefficient (Kc) for the entire growing season considering both fruit yield and vegetative growth. Five irrigation treatments (Kc = 0.50, 0.70, 0.85, 1.0, 1.15) were employed from late winter to the fall over 2 years in a 6-year-old cv. ‘Manzanilla fina’ olive orchard. Tree canopy volume was approximately 15 m³ with a leaf area of about 40 m² at the beginning of the experiment. During much of each year, the volumetric soil water content was lower in the Kc = 0.50 treatment than in the other irrigation levels evaluated (Kc = 0.85 and 1.15). Although differences in midday stem water potential (Ψ_s) were not always apparent between treatments during the first year, there were lower Ψ_s values in Kc = 0.50 and 0.70 relative to the higher irrigation levels during the second year. Shoot elongation in Kc = 0.50 was about 50% of that in Kc = 1.0 and 1.15 during both years leading to significant differences in the increase of tree canopy volume by the end of the first year. Fruit yield was similar among irrigation levels the first year, but yield reached a maximum value the second year between Kc = 0.70 and 0.85 above which no increase was apparent. The somewhat lower fruit yield values in Kc = 0.50 and 0.70 were associated with decreased fruit number rather than reductions in individual fruit weight. The water productivity on a yield basis (fruit yield per mm of applied irrigation) decreased as irrigation increased in the second year, while similar calculations based on trunk cross-sectional area growth indicated that vegetative growth was proportional to the amount of irrigation. This suggests that the warm climate of northwest Argentina (28° S) can induce excessive vegetative growth when very high irrigation levels are applied. A Kc value of approximately 0.70 over the course of the growing season should be sufficient to maintain both fruit yield and vegetative growth at adequate levels. An evaluation of regulated deficit irrigation strategies for table olives in this region could be beneficial to further reduce irrigation.     

Temporal persistence of spatial soil-water patterns under trickle irrigation

Summary Trickle irrigation of perennial crops results in local wetting near trees and vines. Methods to measure soil-water content or storage within the root zone generally require intensive instrumentation to characterize spatial patterns of soil water adequately. The goals of this research were to determine if spatial patterns of soil-water storage under trickle irrigation are temporally presistent which may make it feasible to use less intense sampling to characterize total storage. Soil-water storage from the 0 to 1.5 m soil depth was measured at 23 sites on one side of trickle-irrigated almond trees using a neutron probe over three years in the San Joaquin Valley of California. Measurements were made on two trees in each of five different irrigation treatments. The persistence of spatial patterns with time was evaluated using Spearman rank correlation and relative differences from mean values. Spatial patterns were different for each tree and irrigation treatment but remained fairly persistent with time during a season. In many cases, temporal changes in soil-water storage were adequately estimated from a single location. Single sampling locations identified during one year gave estimates of mean storage during the following year with some increase in error. However, use of the same sampling locations for more than two years increased the error in storage estimates. Soil-water content or storage in trickle-irrigated orchards may be monitored by intense sampling during the early part of the irrigation season in order to identify locations giving mean soil-water storage. Only these locations may then be sampled to monitor changes in soil water.     

Economic analysis of trickle irrigation system considering planting geometry

The aim of the present study is to determine the effect of the planting geometry on yield, capital cost, operating cost and net return for the banana crop planted in a 1-ha² area and irrigated using a trickle irrigation system. The cost analysis was carried out based on yield results obtained under different planting geometry pattern at 2 m, 3 m, 4 m and 5 m row spacing for one to four plants transplanted separately at a place, always with the same number of plants per hectare. The net return was found to be maximum for one plant at a place at 2-m spacing. It was found that the length to breadth ratio of planting has high correlation with the initial capital cost and the total annual cost. The highest return in investiment was obtained at 4-m spacing with 2 plants per location. Analysis was carried out to study the effect of market price of banana, water price and irrigation level (IL) on B/C ratio and net return.     

Numerical evaluation of subsurface trickle irrigation with brackish water

In this study, an assessment for a proposed irrigation system in the El-Salam Canal cultivated land, Egypt, was conducted. A numerical model (HYDRUS-2D/3D) was applied to investigate the effect of irrigation amount, frequency, and emitter depth on the wetted soil volume, soil salinity levels, and deep percolation under subsurface trickle irrigation (SDI) of tomato growing with brackish irrigation water in three different soil types. The simulations indicated that lower irrigation frequency increased the wetted soil volume without significant increase in water percolates below the plant roots. Deep percolation decreased as the amount of irrigation water and emitter depth decreased. With the same amount of irrigation water, the volume of leached soil was larger at lower irrigation frequency. The salinity of irrigation water under SDI with shallow emitter depth did not show any significant effect on increasing the soil salinity above tomato crop salt tolerance. Based on the results, it appears that the use of SDI with brackish irrigation water is an effective method for growing tomato crop in El-Salam Canal cultivated land especially with shallow emitter depth.     

Analysis of soil wetting and solute transport in subsurface trickle irrigation

The increased use of trickle or drip irrigation is seen as one way of helping to improve the sustainability of irrigation systems around the world. However, soil water and solute transport properties and soil profile characteristics are often not adequately incorporated in the design and management of trickle systems. In this paper, we describe results of a simulation study designed to highlight the impacts of soil properties on water and solute transport from buried trickle emitters. The analysis addresses the influence of soil hydraulic properties, soil layering, trickle discharge rate, irrigation frequency, and timing of nutrient application on wetting patterns and solute distribution. We show that (1) trickle irrigation can improve plant water availability in medium and low permeability fine-textured soils, providing that design and management are adapted to account for their soil hydraulic properties, (2) in highly permeable coarse-textured soils, water and nutrients move quickly downwards from the emitter, making it difficult to wet the near surface zone if emitters are buried too deep, and (3) changing the fertigation strategy for highly permeable coarse-textured soils to apply nutrients at the beginning of an irrigation cycle can maintain larger amounts of nutrient near to and above the emitter, thereby making them less susceptible to leaching losses. The results demonstrate the need to account for differences in soil hydraulic properties and solute transport when designing irrigation and fertigation management strategies. Failure to do this will result in inefficient systems and lost opportunities for reducing the negative environmental impacts of irrigation.Communicated by J. Annandale     

Application efficiency of micro-sprinkler irrigation of almond trees

Micro-sprinklers are becoming a preferred irrigation method for water application in orchards. However, there is relatively little data available to support a particular irrigation scheduling method. The objective of this study is to quantify the components of the water balance of an almond tree under micro-sprinkler irrigation. For that purpose, an experimental plot around an almond tree with an area of 2.0 m X 2.0 m without vegetation, representing about one quarter of the wetted area of the micro-sprinkler was instrumented with neutron access tubes, tensiometers and catch cans. Twenty-five access tubes with catch cans were distributed in a square grid of 0.5 m × 0.5 m, to a depth of 0.9 m. Eight pairs of tensiometers were installed at depths of 0.825 and 0.975 m within the experimental plot. During a 7-day period in August, 1995 the plot was sprinkler-irrigated on three days, and water application rates and uniformity coefficients were calculated for each irrigation event. Neutron probe readings at 15 cm depth increments and tensiometer readings were taken 4 to 6 times daily. Results showed large evaporation losses during and immediately after the irrigations. Evaporation losses of the wetted area was estimated to be between 2 and 4 mm/irrigation event. Consequently, application efficiencies were only 73–79%, the wetting of the root zone was limited to the 0–30 cm depth interval only, the soil profile was depleted of soil water, and daily crop coefficient values at days between irrigation events were between 0.6 and 0.8. The study recommends irrigation in the evening and night hours, thereby largely eliminating the evaporation losses that occur during daytime irrigation hours.     

Regulated deficit irrigation during the kernel-filling period and optimal irrigation rates in almond

The use of Regulated deficit irrigation (RDI) in almond, applied during the kernel-filling phase, was evaluated over four consecutive years. To determine the reference optimal irrigation rate, three treatments were applied: T-100, which was irrigated by replacing crop evapotranspiration; T-130, which was irrigated by applying 30% more water than in T-100 and T-70, which received 30% less water than T-100. The RDI treatment received the same irrigation rate as T-100, but during the kernel-filling period irrigation was reduced to 20% of T-100. The optimum yield response was observed in treatment T-100, while T-130 trees never improved on T-100 kernel production over the 4 years of the study. During the first two experimental years, kernel dry matter accumulation did not decrease with drought in the RDI treatment. However, both cropping and kernel growth were reduced during the third and fourth years of the experiment. A possible explanation for this decrease could be found in a hypothetical depletion of the carbohydrate reservoir in RDI trees and also to the negative soil water balance that was evident in the T-70 and RDI treatments during winter and spring of the last 2 years. Although yield reductions for RDI trees were significant (20% with respect to T-100), the water savings obtained (about 60% of that applied with respect to T-100), may help to promote the adoption of RDI in areas, where water availability has been reduced. Bearing in mind the water conservation aspect in almond, RDI, as applied in this case, seemed more interesting than a seasonal sustained deficit irrigation strategy like T-70.     

Cotton-root distribution as a function of trickle irrigation emitter depth

Summary The objective of this study was to evaluate the distribution of cotton (Gossypium hirsutum cv GSA 71) root system under four depths of trickle irrigation emitter. Cotton was grown on an Amarillo fine sandy loam (fine loamy, mixed thermic Aridic Paleustalf) at Lubbock, Texas. Trickle irrigation was applied at the surface (0), 0.15, 0.3, or 0.45 m depths in amounts calculated using daily pan evaporation, crop coefficient, and crop development stage. Effects of depth of trickle irrigation were evaluated by measuring the cotton root-length density in 0.15 m increments to the 0.90 m depth at distances of 0, 0.25, and 0.5 m perpendicular to the cotton rows. The root-length distributions were not significantly (0.05%) different in the top 0.15 m when the surface irrigated treatment was compared with the 0.45 m irrigation depth treatment. Root-length densities for the 0.15 and 0.3 m treatments were not significantly different from one another nor were they different from treatments within the evaluated zones (0 to 0.3 m or 0.15 to 0.45 m). Root-length density within the 0.3 to 0.6 m zone, was not significantly different for the 0.45 m treatment compared with the surface irrigation treatment. Root-length density in the 0.6 to 0.9 m zone was not significantly different for any treatment. Emitter depth of trickle irrigation did not significantly influence the depth or distribution of cotton-root development.     

Evapotranspiration and responses to irrigation of broccoli

In cold, semi-arid areas, the options for crop diversification are limited by climate and by the water supply available. Growing irrigated crops outside the main season is not easy, because of climatic and market constraints. We carried out an experiment in Albacete, Central Spain, to measure the water use (evapotranspiration, ET) of broccoli (Brassica oleracea L. var. italica Plenck) planted in late summer and harvested at the end of fall. A weighing lysimeter was used to measure the seasonal ET under sprinkler irrigation. Consumptive use reached 359 mm for a period of 109 days after transplanting. The crop coefficient (K_c) for broccoli was obtained and compared to the standard recommendations for normal planting dates. Dual crop coefficient computations of the lysimeter ET data indicated that evaporation represented 31% of seasonal ET. An analysis of the variation in daily K_c values at a time of full cover suggested that the use of a grass lysimeter as a reference ET (ET_o) was superior to using the ASCE Penman-Monteith (ASCE PM) equation at hourly time steps, which in turn caused less variability in K_c than when using the FAO-56 Penman-Monteith (FAO-56 PM) equation at daily time steps for the ET_o calculation. An additional experiment aimed at evaluating the yield response to applied irrigation water by the drip method (seven treatments, from 59 to 108% of ET_c) generated a production function that gave maximum yields of near 12 t ha⁻¹ at an irrigation level of 345 mm, and a water use efficiency of 3.37 kg m⁻³. It is concluded that growing broccoli in the fall season is a viable alternative for crop diversification, as the lower yields obtained here may be more than compensated for by the higher produce prices in autumn, at a time of the year where irrigation water demand for other crops is very low.     

Responses of five almond cultivars to irrigation: Photosynthesis and leaf water potential

In the Trás-os-Montes region, almond orchards are usually planted in the dry soils on the upper valley of the Douro river and are typically cultivated under non-irrigated conditions, leading to low yields. This study aimed to compare the physiological responses of five almond varieties (Francoli, Ferragnès, Glorieta, Lauranne and Masbovera) growing under non-irrigated and irrigated conditions. In irrigated conditions, all cultivars had higher photosynthetic rates, with maximum rates in a range of 10–12 μmol CO₂ m⁻² s⁻¹. Study of daily photosynthesis (June–August) indicates that, irrigated plants showed maximal values at 11 h (32 °C), while in water stressed ones highest values were found at 9 h (28 °C). The irrigation induced an increase in photosynthesis of around 173% in Lauranne, 187% in Francoli, 204% in Glorieta, 266% in Masbovera and 331% in Ferragnès. In relation to values of water potential that allow half-rate of photosynthesis (ψ_w50), they were calculated as −2.95, −2.50, −3.10, −3.20 and −3.30 MPa for Ferragnès, Glorieta, Masbovera, Francoli and Lauranne, respectively.     

Comparison of sprinkler,trickle and furrow irrigation efficiencies for onion production

In the Mesilla Valley of southern New Mexico, furrow irrigation is the primary source of water for growing onions. As the demand for water increases, there will be increasing competition for this limited resource. Water management will become an essential practice used by farmers. Irrigation efficiency (IE) is an important factor into improving water management but so is economic return. Therefore, our objectives were to determine the irrigation efficiency, irrigation water use efficiency (IWUE) and water use efficiency (WUE), under sprinkler, furrow, and drip irrigated onions for different yield potential levels and to determine the IE associated with the amount of water application for a sprinkler and drip irrigation systems that had the highest economic return.Maximum IE (100%) and economic return were obtained with a sprinkler system at New Mexico State University’s Agriculture Science Center at Farmington, NM. This IE compared with the 54–80% obtained with the sprinkler irrigation used by the farmers. The IEs obtained for onion fields irrigated with subsurface drip irrigation methods ranged from 45 to 77%. The 45% represents the nonstressed treatments, in which an extra amount of irrigation above the evapotranspiration (Et) requirement was applied to keep the base of the onion plates wet. The irrigation water that was not used for Et went to deep drainage water. The return on the investment cost to install a drip system operated at a IE of 45 was 29%. Operating the drip system at a IE of 79% resulted in a yield similar to surface irrigated onions and consequently, it was not economical to install a drip system. The IEs at the furrow-irrigated onion fields ranged from 79 to 82%. However, the IEs at the furrow-irrigated onion fields were high because farmers have limited water resources. Consequently, they used the concept of deficit irrigation to irrigate their onion crops, resulting in lower yields. The maximum IWUE (0.084 t ha⁻¹ mm⁻¹ of water applied) was obtained using the sprinkler system, in which water applied to the field was limited to the amount needed to replace the onions’ Et requirements. The maximum IWUE values for onions using the subsurface drip was 0.059 and 0.046 t ha⁻¹ mm⁻¹ of water applied for furrow-irrigated onions. The lower IWUE values obtained under subsurface drip and furrow irrigation systems compared with sprinkler irrigation was due to excessive irrigation under subsurface drip and higher evaporation rates from fields using furrow irrigation. The maximum WUE for onions was 0.009 t ha⁻¹ mm⁻¹ of Et. In addition, WUE values are reduced by allowing the onions to suffer from water stress.     

Distribution of water and salt in soil under trickle and pot irrigation regimes

An ellipitical clay pot was buried vertically in the centre of a lysimeter as a means of supplying water to the soil. The distribution of water and salt in the soil emerging from the pot source was compared with that under trickle irrigation. Five hundred milliequivalents of calcium chloride was applied to the soil by both methods. Calcium chloride was subsequently leached by applying 50 l of tap water. The soil solution was sampled periodically using suction cups. Soil samples were also taken for measurements of water content and chloride ion concentration. Water applied at the rate of 130 ml/h by the pot moved the salt to a radial distance of 41.5 cm in 390 h, but applying water by trickle at the rate of one l/h moved the salt 42 cm in 52.5 h. For an equal amount of water applied, salt moved deeper in the profile at the lower application rate. More salt spreading was observed from the trickle source with higher application rate. After 72 h of redistribution, the wetted volumes were approximately equal for trickle and pot irrigation regimes.     

Factors affecting success and failure of trickle irrigation systems in Balochistan,Pakistan

An evaluation of performance of trickle irrigation systems installed in Balochistan, Pakistan during 1982–2002 was conducted by field surveys, physical verifications and interviews with farmers. Thirty systems were fully or partially operational and 76 had been abandoned. Successful systems required clean and reliable water supply, availability of spare components and accessories for replacements, skilled manpower, and a high level of interest and participation by the owner. The dominant species irrigated with these trickle systems were apples, grapes, and mixed orchards. Installations of trickle systems on old mature orchards were not generally successful due to lack of adaptation of the new system to limited and scheduled irrigation supplies. Many of the irrigators were not instructed on how to adjust the trickle system to meet changing needs of the plants. Consequently, growth of some of the trees was stunted and a few of them died. Lack of technical skill to repair and maintain the system and non-availability of replacement parts were general causes of failure of installed trickle irrigation systems. Clogging of the emitters was the primary specific cause of failure. Emitters with a larger opening that will not be clogged by most of the contaminants contained in the water available to these farmers and turbulent action screening systems to take out the other contaminants are proposed as solutions to this problem. Commercial shops, which sell the components, carry replacement parts and provide after-sales service are needed to keep trickle systems functioning in these isolated areas.