Yield and fibre quality of cotton cultivars as affected by the build-up of sodium in the soils with sustained sodic irrigations under semi-arid conditions

Cotton is commonly grown in many arid and semi-arid regions of the world having sodic ground waters. A field plot study was, therefore, conducted for 2 years to study the effect of sustained sodic irrigation on yield and fibre quality of two hirustum cotton cultivars (F-505 and F-846) and one arborium cultivar (LD-327). The exchangeable sodium percentage (ESP) of 0–30 cm soil under sustained canal water (CW) irrigation treatment was 3.5 whereas long-term irrigations (for more than 10 years) with sodic waters having residual sodium carbonate (RSC) of 5, 10 and 15 me l⁻¹ resulted in ESP bulid-up of 16.4, 39.6 and 56.2, respectively. These sodic waters were used for irrigation in the respective plots, for both years of the study. High ESP of the soil decreased the growth (in terms of plant height) and yield of all the three cotton cultivars. The rate of decline in plant height at 50, 80 and 140 days of sowing (DAS) was maximum in F-505 and minimum in F-846. Compared with CW treatment, relative seed-cotton yield under 16.4, 39.6 and 56.2 ESP levels obtained with respective sodic water treatments for 2 years were 99, 70 and 69%, respectively in F-846, 101, 46 and 29%, respectively in F-505 and 98, 67 and 49%, respectively in LD-327. Similar trends were observed in case of boll number per square metre and boll weight. The cultivar F-846 produced heavier bolls than the other two cultivars under ESP levels of 56.2 obtained under RSC₁₅ treatment which helped this cultivar to perform relatively better. The harmful effect of sodic waters on fibre quality (2.5% span length, micronaire value and bundle strength) were also not observed in the case of F-846. A slight deterioration in fibre quality was, however, observed in cultivars F-505 and LD-327 at an ESP of 56.2 in the soil.     

Effect of irrigation methods,management and salinity of irrigation water on tomato yield,soil moisture and salinity distribution

The increasing demand for irrigation water to secure food for growing populations with limited water supply suggests re-thinking the use of non-conventional water resources. The latter includes saline drainage water, brackish groundwater and treated waste water. The effects of using saline drainage water (electrical conductivity of 4.2–4.8 dS m⁻¹) to irrigate field-grown tomato (Lycopersicon esculentum Mill cv Floradade) using drip and furrow irrigation systems were evaluated, together with the distribution of soil moisture and salt. The saline water was either diluted to different salinity levels using fresh water (blended) or used cyclically with fresh water. The results of two seasons of study (2001 and 2002) showed that increasing salinity resulted in decreased leaf area index, plant dry weight, fruit total yield and individual fruit weight. In all cases, the growth parameters and yield as well as the water use efficiency were greater for drip irrigated tomato plants than furrow-irrigated plants. However, furrow irrigation produced higher individual fruit weight. The electrical conductivity of the soil solution (extracted 48 h after irrigation) showed greater fluctuations when cyclic water management was used compared to those plots irrigated with blended water. In both drip and furrow irrigation, measurements of soil moisture one day after irrigation, showed that soil moisture was higher at the top 20 cm layer and at the location of the irrigation water source; soil moisture was at a minimum in the root zone (20–40 cm layer), but showed a gradual increase at 40–60 and 60–90 cm and was stable at 90–120 cm depth. Soil water content decreased gradually as the distance from the irrigation water source increased. In addition, a few days after irrigation, the soil moisture content decreased, but the deficit was most pronounced in the surface layer. Soil salinity at the irrigation source was lower at a depth of 15 cm (surface layer) than that at 30 and 60 cm, and was minimal in deeper layers (i.e. 90 cm). Salinity increased as the distance from the irrigation source increased particularly in the surface layer. The results indicated that the salinity followed the water front. We concluded that the careful and efficient management of irrigation with saline water can leave the groundwater salinity levels unaffected and recommended the use of drip irrigation as the fruit yield per unit of water used was on average one-third higher than when using furrow irrigation.     

Effect of stage-specific saline irrigation on greenhouse tomato production

In many water scarce areas, saline water has been included as an important substitutable resource in agricultural irrigation. It would be of practical use to investigate the effect of stage-specific saline irrigation on yield, fruit quality, and other growth responses of greenhouse tomato, to establish a proper irrigation management strategy for tomato production in these regions. Here, saline irrigations (3.33, 8.33, and 16.67 dS m⁻¹ NaCl solution) were applied during four growth stages of greenhouse tomato (L. esculentum Mill. cv. Zhongza No. 9) grown in the North China Plain, respectively. These include flowering and fruit-bearing stage (stage 1), first cluster fruit expanding stage (stage 2), second cluster fruit expanding stage (stage 3), and harvesting stage (stage 4). Compared with the following three stages, yield loss was most remarkable in stage 1 under all three salinity levels. Under irrigation practices using 3.33 dS m⁻¹ saline water in all four stages, 8.33 dS m⁻¹ saline water in latter three stages, and 16.67 dS m⁻¹ saline water in stage 4, yield reduction was not significant while fruit quality was improved. In conclusion, it is feasible to use stage-specific saline irrigation for tomato production in water scarce areas like North China Plain.     

Effect of subsurface drip irrigation on onion yield

Subsurface drip system is the latest method of irrigation. The design of subsurface drip system involves consideration of structure and texture of soil, and crop’s root development pattern. A 3-year experiment was conducted on onion (Allium Cepa L., cv. Creole Red) in a sandy loam soil from October to May in 2002–2003, 2003–2004 and 2004–2005 to study the effect of depth of placement of drip lateral and different levels of irrigation on yield. Tests for uniformity of water application through the system were carried out in December of each year. Three different irrigation levels of 60, 80 and 100% of the crop evapotranspiration and six placement depths of the drip laterals (surface (0), 5, 10, 15, 20 and 30 cm) were maintained in the study. Onion yield was significantly affected by the placement depth of the drip lateral. Maximum yield (25.7 t ha⁻¹) was obtained by applying the 60.7 cm of irrigation water and by placing the drip lateral at 10 cm soil depth. Maximum irrigation water use efficiency (IWUE) (0.55 t ha⁻¹ cm⁻¹) was obtained by placing the drip lateral at 10 cm depth. The greater vertical movement of water in the sandy-loam soil took place because of the predominant role of gravity rather than that of the capillary forces. Therefore, placement of drip lateral at shallow depths is recommended in onion crop to get higher yield.     

Tomato root distribution, yield and fruit quality under different subsurface drip irrigation regimes and depths

Tomato rooting patterns, yield and fruit quality were evaluated in a field trial where three irrigation regimes [0.6 (DI), 0.9 (DII) and 1.2 ET_c (DIII)] and three drip irrigation depths [surface (R0), subsurface at 20 cm depth (RI) and subsurface at 40 cm depth (RII)] were imposed following a split-plot experimental design, with four replications. The behaviour of the root system in response to the irrigation treatments was evaluated using minirhizotrons installed between two plants, near the plant row. Root-length intensity (L _a)—length of the root per unit of minirhizotron surface area (cm cm⁻²)—was measured at four crop stages. For all sampling dates, none of the factors studied were found to influence L _a or rooting depth significantly or the interaction between treatments. For all treatments most of the root system was concentrated in the top 40 cm of the soil profile, where the root-length density ranged from 0.5 cm cm⁻³ to 1.4 cm cm⁻³ . The response of tomato fruits to an increase in the water applied was similar in quantitative and qualitative terms for the different drip irrigation depths. Water applied by drip irrigation had the opposite effect on commercial yield (t ha⁻¹) and soluble solids (°Brix) (r=−0.82, P<0.001), however, yield in terms of total soluble solids (t ha⁻¹) was the same for the 0.9 and 1.2 ET_c. The increase in commercial yield can be described by the equation      

Evaluation of the influence of irrigation methods and water quality on sugar beet yield and water use efficiency

Rapid urbanization and industrialization have increased the pressure on limited existing fresh water to meet the growing needs for food production. Two immediate responses to this challenge are the efficient use of irrigation technology and the use of alternative sources of water. Drip irrigation methods may play an important role in efficient use of water but there is still limited information on their use on sugar beet crops in arid countries such as Iran. An experiment was conducted to evaluate the effects of irrigation method and water quality on sugar beet yield, percentage of sugar content and irrigation water use efficiency (IWUE). The irrigation methods investigated were subsurface drip, surface drip and furrow irrigation. The two waters used were treated municipal effluent (EC = 1.52 dS m⁻¹) and fresh water (EC = 0.509 dS m⁻¹). The experiments used a split plot design and were undertaken over two consecutive growing seasons in Southern Iran. Statistical testing indicated that the irrigation method and water quality had a significant effect (at the 1% level) on sugar beet root yield, sugar yield, and IWUE. The highest root yield (79.7 Mg ha⁻¹) was obtained using surface drip irrigation and effluent and the lowest root yield (41.4 Mg ha⁻¹) was obtained using furrow irrigation and fresh water. The highest IWUE in root yield production (9 kg m⁻³) was obtained using surface drip irrigation with effluent and the lowest value (3.8 kg m⁻³) was obtained using furrow irrigation with fresh water. The highest IWUE of 1.26 kg m⁻³ for sugar was obtained using surface drip irrigation. The corresponding efficiency using effluent was 1.14 kg m⁻³. Irrigation with effluent led to an increase in the net sugar yield due to an increase in the sugar beet root yield. However, there was a slight reduction in the percentage sugar content in the plants. This study also showed that soil water and root depth monitoring can be used in irrigation scheduling to avoid water stress. Such monitoring techniques can also save considerable volumes of irrigation water and can increase yield.     

Effects of diluted Kraft pulp mill effluent on hybrid poplar and soil chemical properties

Irrigation with effluents can detrimentally affect soil physical and chemical properties and impact plant growth and development. Excessive irrigation can leach salts from the root zone; which can be accomplished by precipitation in some areas. This study was conducted to examine the effect of applications of Kraft pulp mill effluent (KPME) with and without distilled water (DW) to simulate precipitation would have on soil chemical properties and growth of hybrid poplar (Populus deltoides × P. petrowskyana L. cv. Walker). Distilled water (DW), KPME, and a 50% combination (v/v; COMB) of DW and KPME were applied at rates of 6 and 9 mm day⁻¹. COMB resulted in heights, biomasses, and leaf areas that were greater than those for KPME and comparable to those for DW. Diluted KPME treatments (i.e., COMB) still significantly increased soil electrical conductivity and sodium adsorption ratio compared to DW. Leachate collected from KPME 9 mm day⁻¹ had concentrations of HCO₃ ⁻, SO₄ ²⁻, Cl⁻, Ca²⁺, K⁺, and Mg²⁺ comparable to those collected from COMB 9 mm day⁻¹, but Na⁺ concentrations were three times higher in KPME than COMB 9 mm day⁻¹. Results indicate that precipitation or additional irrigation water could potentially provide the leaching necessary to prevent salt accumulation within the rooting zone; however, irrigating with saline or sodic effluents requires careful management.     

Managing subsurface drip irrigation in the presence of shallow ground water

A 3-year project compared the operation of a subsurface drip irrigation (SDI) and a furrow irrigation system in the presence of shallow saline ground water. We evaluated five types of drip irrigation tubing installed at a depth of 0.4 m with lateral spacings of 1.6 and 2 m on 2.4 ha plots of both cotton and tomato. Approximately 40% of the cotton water requirement and 10% of the tomato water requirement were obtained from shallow (<2 m) saline (5 dS/m) ground water. Yields of the drip-irrigated cotton improved during the 3-year study, while that of the furrow-irrigated cotton remained constant. Tomato yields were greater under drip than under furrow in both the years in which tomatoes were grown. Salt accumulation in the soil profile was managed through rainfall and pre-plant irrigation. Both drip tape and hard hose drip tubing are suitable for use in our subsurface drip system. Maximum shallow ground water use for cotton was obtained when the crop was irrigated only after a leaf water potential (LWP) of −1.4 MPa was reached. Drip irrigation was controlled automatically with a maximum application frequency of twice daily. Furrow irrigation was controlled by the calendar.     

Varietal differences in the response of durum wheat (Triticum turgidum L. var. durum) to irrigation strategies in a semi-arid region of Algeria

The response of three durum wheat cultivars (C: Chen’s, V: Vitron, W: Waha) to irrigation was studied during 4 years in semi-arid Algeria (Chlef). The four treatments were NI (unirrigated), EI (early irrigation, up to heading), LI (late irrigation, from heading) and FI (full irrigation, over the entire season). FI increased rainfed grain yield (1,300 kg ha⁻¹) by 270%, EI by 107%, and LI by 67%. The variety × irrigation interaction was significant each year. Under irrigation, cv. Vitron was generally the most productive cultivar while in rainfed conditions cv. Waha always resulted in the highest grain yield. Grain yield increased exponentially with seasonal evapotranspiration (r ² = 0.741) and harvest index (r ² = 0.873). Water use efficiency for grain ranged from 4.6–5.3 kg ha⁻¹ mm⁻¹ (NI) to 9.6–10.8 kg ha⁻¹ mm⁻¹ (FI) as a function of cultivar and irrigation, cv. Vitron and cv. Waha (full irrigation) and cv. Waha (rainfed) being the most efficient cultivars. According to the evaporation pan method, the seasonal crop coefficient (K _c) values for the three cultivars were 0.64 (V), 0.62 (W) and 0.54 (C). The corresponding peak K _c values were 1.0, 0.97 and 0.89, respectively. K _c was closely related to leaf area index (LAI) and specific logarithmic relationships were calculated for each cultivar. Irrigation scheduling should be adapted to the type of cultivar in relation to its potential yield and LAI development pattern.     

Water stress imposed on muskmelon (Cucumis Melo L.) with subsurface and surface drip irrigation systems under semi-arid climatic conditions

In 2005 and 2006, a study was conducted to determine the effect of subsurface and surface drip irrigation systems and to determine optimum irrigation water using six different irrigation levels imposed on muskmelon (Cucumis Melo L. cv. Ananas F1) under semi-arid climatic conditions. Irrigation treatments received 0, 25, 50, 75, 100, and 125% of class A pan evaporation rates. In 2005, average yield from subsurface and surface drip irrigation systems ranged from 16.2 (I ₀) to 31.1 (I ₇₅) t ha⁻¹ and from 16.2 (I ₀) to 43.8 (I ₇₅) t ha⁻¹, respectively. While in 2006, fruit yields for the same systems ranged from 8.2 (I ₀) to 40.4 (I ₇₅) t ha⁻¹ and from 8.2 (I ₀) to 38.9 (I ₁₀₀) t ha⁻¹. Regression analysis of the yield data indicated no significant (P > 0.05) difference between years and irrigation systems. The highest muskmelon yields from subsurface and surface drip irrigation systems were obtained at 83 and 92% of class A pan. Bigger fruits were obtained with optimum irrigation amounts for both of the irrigation systems. However, there was no clear indication of irrigation water amounts on total soluble solid and flesh thickness of muskmelon fruits.     

Cotton yields under different furrow irrigation management techniques in the Southeastern Anatolia Project (GAP) area,Turkey

The continuous flow furrow irrigation (COFFI), surge flow furrow irrigation (SUFFI), cutback flow furrow irrigation (CUFFI), variable alternate flow furrow irrigation (VAFFI), and tail water reuse system furrow (TWRSF) techniques with the same inflow rate of 0.072 m³ min⁻¹ were compared in relation to the cotton yield and water use efficiency at a 3-year field study conducted on cotton (Gossypium spp.) in the Southeastern Anatolia Project (GAP) area of Turkey. Yields revealed significant statistical differences between the furrow management techniques (P < 0.05). The maximum yield was obtained from the COFFI treatment (2,630 and 2,920 kg ha⁻¹) in the first 2 years, and from SUFFI and CUFFI treatments (3,690 and 3,780 kg ha⁻¹, respectively) in the last year. There were significant yield reductions, which varied from 10 to 35% in TWRSF and from 11 to 19% in VAFFI treatments although 43 and 28% more water was applied to the TWRSF than to CUFFI and SUFFI treatments, respectively. The average total water use efficiencies (WUE_ET) varied from 4.14 (VAFFI) to 2.59 (COFFI). The corresponding values were 0.37 and 0.36 kg ha⁻¹ m⁻³ for CUFFI and SUFFI, respectively. The average irrigation water use efficiency (WUE_IR) for CUFFI and SUFFI treatments were 0.30 and 0.23 kg ha⁻¹ m⁻³, respectively.     

Response of alfalfa (<Emphasis Type="Italic">Medicago sativa</Emphasis> L.) to diurnal and nocturnal saline sprinkler irrigations. I: total dry matter and hay quality

Little information is available on the quantitative effects on crops of saline sprinkler irrigations and the presumable beneficial effects of nocturnal versus diurnal irrigations. We measured crude protein content, carbon isotope discrimination and total dry matter (TDM) of alfalfa (Medicago sativa L.) subject to diurnal and nocturnal saline sprinkler irrigations. The work was carried out in Zaragoza (Spain) during the 2004–2006 growing seasons with a triple line source sprinkler system using synthetic saline waters dominated by NaCl with an irrigation water EC ranging from 0.5 to 5.6 dS m⁻¹. The quality of alfalfa hay assessed through its crude protein concentration was not significantly affected by salinity. Carbon isotope discrimination, an indicator of the effect of osmotic stress on plant water status, tended to decrease with increases in salinity. Based on a piecewise linear response model, alfalfa grown under saline sprinkler irrigation was shown to be more tolerant (threshold soil salinity, EC_e = 3.5 dS m⁻¹) than in previous experiments under surface irrigation (threshold EC_e = 2.0 dS m⁻¹) at relatively low salinity values, but became more sensitive at higher salinity values as shown by the higher absolute slope (13.4%) for sprinkler as compared to surface irrigation (7.3%). No significant differences in TDM were found between diurnal and nocturnal saline sprinkler irrigations. The recommended practice of irrigating at night for sprinkler irrigation using saline water is therefore not supported by our results in alfalfa grown under semiarid conditions.     

Sediment transport in furrow irrigation

Irrigation-induced erosion in furrow irrigation causes loss of fertile soil and water quality degradation. Hence, quantification of irrigation-induced erosion is essential for efficient management of furrow irrigation. In this study, sediment transport was studied under bare and cropped field conditions for a furrow plot consisting of three parabolic shaped furrows of 40 m long and 0.5% slope. The inflow rates of 0.2, 0.3, 0.4 and 0.5 L s⁻¹; and 0.3, 0.4, 0.5, 0.6 and 0.7 L s⁻¹ were used for bare and cropped field conditions, respectively. The furrow cross section measured at every 5 m distance from the head end (before and after the irrigation event) was used to study the erosion pattern (erosion/deposition) along the furrow. The runoff collected at regular intervals of 10 min was used to study the sediment load. The total sediment export for an irrigation event was estimated using furrow cross-section data (FCD) and the sediment rate data (SRD), and compared with the total sediments collected at the tail end. For both bare and cropped conditions, soil erosion took place at the head and tail ends (free drain system), while the deposition occurred at the middle. The sediment transport increased initially and slightly decreased with time. A power relationship was obtained between the total sediment export and the inflow rate for bare furrow condition, whereas a linear relationship between these parameters was obtained for cropped field condition. The relative percentage errors suggested that both SRD and FCD methods can be used to estimate total sediment export from the field. The analysis (PSD) of the total sediments revealed that the geometric mean diameter of the sediment particle was 0.18 and 0.20 mm for bare and cropped field conditions, respectively.     

Tensiometer-based irrigation scheduling in perennial strawberry cultivation

Tensiometers are ideal for soil moisture monitoring in strawberry cultivation because they operate effectively at less than −1,000 hPa soil water tension, which includes the soil moisture range for strawberries. For this study, four different drip irrigation thresholds, at −150, −300, −600 hPa, and, depending on the development stage of the plants, −300 or −600 hPa, were applied in a trial carried out in southwest Finland in 2001–2003 with June-bearing cultivar ‘Bounty’. Higher soil moisture increased yield and fruit soluble solids content, but decreased fruit firmness. In healthy plants, no remarkable soil moisture effects on plant growth were observed, but in the years 2002–2003 it was observed that increased soil moisture in the previous growing season and the subsequent winter injuries decreased the following year’s growth. Water consumption of plants varied considerably depending on growth stage, yield potential and environmental factors. The volumes of irrigation water ranged from 5 to 22 l/plant per growing season.     

Performance of sugarcane genotypes grown under sodic soil and water conditions

An experiment was conducted to evaluate the effect of residual sodium carbonates (RSC) of irrigation water on the growth and yield of sugarcane grown on sierozem light textured alkaline soil with sodic ground water and to study the performance of some promising sugarcane genotypes under these conditions. Treatments consisted of five levels of irrigations water viz RSC 2.8, 6.5, 12 me l⁻¹ and RSC 6.5 and 12.0 me l⁻¹ fully amended with gypsum. Plant and ratoon crops of eight genotypes of sugarcane were harvested. Cane yield and yield attributing characters like cane height, number of internodes per cane and number of millable canes were recorded. Juice quality viz percent juice extraction, percent sucrose, and commercial cane sugar (CCS%) in juice were determined at the harvest of crop. For both plant and ratoon crops, the average cane yield of all the genotypes of sugarcane and cane yield attributing characters decreased significantly with the increase in RSC of irrigation water to 6.5 and 12.0 me l⁻¹ (35% and 51% decline in the average cane yield for plant crop). For ratoon crop, the corresponding decrease in the average cane yield was less than the plant crop (only 14% and 21%). Amending RSC with gypsum increased the yield in all genotypes. The cane yield of various genotypes obtained under amended RSC with gypsum treatments were almost equal to the yield obtained under RSC 2.8 me l⁻¹ treatment (89% to 92% average cane yield for plant crop and 93% to 96% for ratoon crop). The effect of RSC of irrigation was variable for different genotypes (for example, for the plant crop of CoH 97, 65% and 76% and for CoH 108, 9% and 20% decline in the cane yield was observed with the application of high RSC irrigation water). As compared to plant crop, the ratoon crop of all genotypes recorded higher average cane yield and lesser decline in the cane yield with the application of high RSC irrigation water. Average juice extraction % decreased from 40.5% to 35.8%, and sugar yield decreased significantly (5.61 to 2.91 t ha⁻¹ for plant crop and 6.18 to 5.38 t ha⁻¹ for ratoon crop) with the increase in RSC of irrigation water, and amending RSC with gypsum increased the juice extraction % and sugar yield per unit area.     

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.     

Effects of irrigation method on chile pepper yield and Phytophthora root rot incidence

A field experiment was conducted in 1995 and 1996 to examine the effects of different irrigation methods on yields and Phytophthora root rot disease of chile plants (Capsicum annum New Mexico `6–4'). Three irrigation methods, daily drip, 3-day drip, and alternate row furrow irrigation, were applied to plots infested with P. capsici and uninfested plots. For both years, the drip irrigation (either daily or 3-day) created higher marketable green chile yields than the alternate row furrow irrigation (p < 0.05), and the yields between the daily and 3-day drip irrigation were statistically similar. The effect of irrigation on marketable combined yields was similar to that on green chile yields. In 1995, root rot disease incidence in the infested plots was significantly higher under alternate row furrow irrigation than for daily and 3-day drip irrigation. There was no disease development in the uninfested plots regardless of the irrigation method. The disease decreased green chile yield by 55% (p < 0.1), and combined yield (green + red chile) by 36% (p < 0.1) in 1995 compared to that in uninfested plots in alternate row furrow irrigation. In 1996, however, no disease occurred in any treatment. The results suggested that drip irrigation increases chile yield through providing either favorable soil moisture conditions or unfavorable conditions for Phytophthora propagation.     

Distribution and storage characterization of soil solution for drip irrigation

The increased use of marginal quality water with drip irrigation requires sound fertigation practices that reconcile environmental concerns with viable crop production objectives. We conducted experiments to characterize dynamics and patterns of soil solution within wet bulb formed by drip irrigation. Time-domain reflectometry probes were used to monitor the distribution of potassium nitrate (KNO₃) and water distribution from drippers discharging at constant flow rates of 2, 4 and 8 L h⁻¹ in soil-filled containers. Considering results from different profiles, we observed greater solute storage near the dripper decreasing gradually towards the wetting front. About half of the applied KNO₃ solution (48%) was stored in the first layer (0–0.10 m) for all experiments, 29% was stored in the next layer (0.10–0.20 m). Comparing different dripper flow rates, we observed higher solution storage for 4 L h⁻¹, with 45, 53 and 47% of applied KNO₃ solution accumulating in the first layer (0–0.10 m) for dripper flow rates of 2, 4 and 8 L h⁻¹, respectively. The results suggest that based on the volume and frequency used in this experiment, it would be advantageous to apply small amounts of solution at more frequent intervals to reduce deep percolation losses of applied water and solutes.     

A modified checkbook irrigation method based on GIS-coupled model for regional irrigation scheduling

In this study, a regional irrigation schedule optimization method was proposed and applied in Fengqiu County in the North China Plain, which often suffers serious soil water drainage and nitrogen (N) leaching problems caused by excessive irrigation. The irrigation scheduling method was established by integrating the ‘checkbook irrigation method’ into a GIS-coupled soil water and nitrogen management model (WNMM) as an extension. The soil water and crop information required by the checkbook method, and previously collected from field observations, was estimated by the WNMM. By replacing manually observed data with simulated data from WNMM, the application range of the checkbook method could be extended from field scale to regional scale. The WNMM and the checkbook irrigation method were both validated by field experiments in the study region. The irrigation experiment in fluvo–aquic soil showed that the checkbook method had excellent performance; soil water drainage and N leaching were reduced by 83.1 and 85.6%, respectively, when compared with local farmers’ flood irrigation. Using the validated WNMM, the performance of checkbook irrigation in an entire winter wheat and summer maize rotation was also validated: the average soil water drainage and N leaching in four types of soils decreased from 331 to 75 mm year⁻¹ and 47.7 to 9.3 kg ha⁻¹ year⁻¹, respectively; and average irrigation water use efficiency increased from 26.5 to 57.2 kg ha⁻¹ mm⁻¹. The regional irrigation schedule optimization method based on WNMM was applied in Fengqiu County. The results showed a good effect on saving irrigation water, decreasing soil water drainage and then saving agricultural inputs. In a typical meteorological year, it could save >110 mm of irrigation water on average, translating to >7.26 × 10⁷ m³ of agricultural water saved each year within the county. Annual soil water drainage was reduced to <143 mm and N leaching to <27 kg ha⁻¹ in most soils, all of which were significantly lower than local farmers’ flood irrigation. In the mean time, crop yield also had an average increase of 2,890 kg ha⁻¹ when checkbook irrigation was applied.     

Differences in water-use efficiency among perennial forages used by the dairy industry under optimum and deficit irrigation

The cost and scarcity of water is placing increasing pressure on Australian dairy farmers to utilise water for forage production as efficiently as possible. This study aimed to identify perennial forage species with greater water-use efficiency (WUE) than the current dominant species, perennial ryegrass (Lolium perenne L.). Fifteen perennial forage species were investigated under optimum irrigation and two deficit irrigation treatments, over three years at Camden, NSW, on a brown Dermsol in a warm temperate climate. Under optimal irrigation, there was a nearly twofold difference in mean WUE_t (total yield/evapotranspiration) between forages, with kikuyu (Pennisetum clandestinum Hochst. ex. chiov.) having the highest (27.3 kg ha⁻¹ mm⁻¹) and birdsfoot trefoil (Lotus corniculatus L.) the lowest (14.8 kg ha⁻¹ mm⁻¹). Kikuyu was also the most water use efficient forage under the extreme deficit irrigation treatment, although its mean WUE_t declined by 15% to 23.2 kg ha⁻¹ mm⁻¹, while white clover (Trifolium repens L.) in the same treatment had the largest decline of 44% and the lowest WUE_t of only 8.8 kg ha⁻¹ mm⁻¹. In order to maximise WUE for any forage, it is necessary to maximise yield, as there is a strong positive relationship between yield and WUE_t.