Comparative affects of blending,intera/inter-seasonal cyclic uses of alkali and good quality waters on soil properties and yields of paddy and wheat

Degradation of soils irrigated with the ground waters having residual alkalinity constitutes a major threat to irrigated agriculture in semi-arid parts especially the South Asia. Paddy–wheat has come to stay as the major crop rotation in the afflicted areas, which is either irrigated solely with alkali waters (AW) or combined with good quality water supplies through canal networks. Therefore, to develop appropriate conjunctive use strategies for the latter situations, response of paddy and wheat was evaluated to the combined use of a good quality water (GW, EC_iw 0.5, RSC nil) and that having residual alkalinity (AW, EC_w 2.3 dS m⁻¹, RSC 11.3 mequiv L⁻¹, SAR_w 15 mmol L^0.5) for 6 years (1997–2003) in lysimeters (2.0 m deep, 0.9 m i.d., with drainage outlets at the bottom) filled in with a sandy loam soil (pH 7.8, ESP 5.3). Increase in soil pH (8.71), salinity (3.8 dS m⁻¹) and sodicity (ESP 27.3) as a consequence of irrigation with alkali water markedly affected the yields of both the crops. The sustainability yield index (SYI) was 0.522 and 0.793 for paddy and wheat, respectively, indicating the sensitivity of the former to the use of alkali water. Keeping the AW input to be similar through irrigations, the SYI for paddy with blending of GW and AW in the ratio of 2:1, 1:1 and 1:2 was 0.732, 0.708 and 0.678, respectively, when compared with 0.751, 0.729 and 0.701 under intera-seasonal cyclic uses. Similarly, the SYI of wheat ranged between 0.821–0.907 and 0.853–0.949 with blending and cyclic uses of the two waters, indicating thereby a yield advantage with the latter. When the two waters were rotated inter-seasonally, the dilution effects of monsoon rains helped to induce greater use of AW for paddy. The overall deterioration in soil properties under different modes was related to proportion of AW applied. It was concluded that the alternating good quality and alkali waters could be a better way to alleviate sodicity problems caused with the use of alkali water alone.     

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.     

Soil salinity related to physical soil characteristics and irrigation management in four Mediterranean irrigation districts

Irrigated agriculture is threatened by soil salinity in numerous arid and semiarid areas of the Mediterranean basin. The objective of this work was to quantify soil salinity through electromagnetic induction (EMI) techniques and relate it to the physical characteristics and irrigation management of four Mediterranean irrigation districts located in Morocco, Spain, Tunisia and Turkey. The volume and salinity of the main water inputs (irrigation and precipitation) and outputs (crop evapotranspiration and drainage) were measured or estimated in each district. Soil salinity (EC_e) maps were obtained through electromagnetic induction surveys (EC_a readings) and district-specific EC_a-EC_e calibrations. Gravimetric soil water content (WC) and soil saturation percentage (SP) were also measured in the soil calibration samples. The EC_a-EC_e calibration equations were highly significant (P < 0.001) in all districts. EC_a was not significantly correlated (P > 0.1) with WC, and was only significantly correlated (P < 0.1) with soil texture (estimated by SP) in Spain. Hence, EC_a mainly depended upon EC_e, so that the maps developed could be used effectively to assess soil salinity and its spatial variability. The surface-weighted average EC_e values were low to moderate, and ranked the districts in the order: Tunisia (3.4 dS m⁻¹) > Morocco (2.2 dS m⁻¹) > Spain (1.4 dS m⁻¹) > Turkey (0.45 dS m⁻¹). Soil salinity was mainly affected by irrigation water salinity and irrigation efficiency. Drainage water salinity at the exit of each district was mostly affected by soil salinity and irrigation efficiency, with values very high in Tunisia (9.0 dS m⁻¹), high in Spain (4.6 dS m⁻¹), moderate in Morocco (estimated at 2.6 dS m⁻¹), and low in Turkey (1.4 dS m⁻¹). Salt loads in drainage waters, calculated from their salinity (EC_dw) and volume (Q), were highest in Tunisia (very high Q and very high EC_dw), intermediate in Turkey (extremely high Q and low EC_dw) and lowest in Spain (very low Q and high EC_dw) (there were no Q data for Morocco). Reduction of these high drainage volumes through sound irrigation management would be the most efficient way to control the off-site salt-pollution caused by these Mediterranean irrigation districts.     

Water and salt balance at irrigation scheme scale: A comprehensive approach for salinity assessment in a Saharan oasis

Salt balance methods are generally applied in the root-zone and at local scales but do not provide relevant information for salinity management at irrigation scheme scales, where there are methodological impediments. A simple salt balance model was developed at irrigation scheme and yearly time scales and applied in Fatnassa oasis (Nefzaoua, Tunisia). It accounts for input by irrigation, export by drainage and groundwater flow, and provides novel computation of the influence of biogeochemical processes and variations in the resident amount of salt for each chemical component in the soil and shallow groundwater. Impediments were overcome by limiting the depth of the system so that the resident amount of salt that remained was of the same order of magnitude as salt inputs and allowed indirect and reliable estimation of groundwater flow. Sensitivity analyses as partial derivatives of groundwater salinity were carried out according to non-reactive salt balance under steady-state assumption. These analyses enabled the magnitude of the salinization process to be foreseen as a function of hydrological changes linked to irrigation, drainage, groundwater flow and extension of the irrigated area. From a salt input of 39 Mg ha⁻¹ year⁻¹ by irrigation, 21 Mg ha⁻¹ year⁻¹ (54%) and 10 Mg ha⁻¹ year⁻¹ (26%) were exported by groundwater flow and drainage, respectively. 7 Mg ha⁻¹ year⁻¹ (18%) were removed from groundwater by geochemical processes, while a non-significant 2 Mg ha⁻¹ year⁻¹ were estimated to have been stored in the soil and shallow groundwater where the residence time was only 2.7 years. The leaching efficiency of drainage was estimated at 0.77. With a water supply of 1360 mm by irrigation and 90 mm by rainfall, drainage, groundwater flow and actual evapotranspiration were 130, 230, and 1090 mm, respectively. The current extension of date palm plantations and salinization of groundwater resources are expected to significantly increase the salinity hazard while the degradation of the drainage system is expected to be of lesser impact. The approach was successfully implemented in Fatnassa oasis and proved to be particularly relevant in small or medium irrigation schemes where groundwater fluxes are significant.     

Yield and water-production functions of two durum wheat cultivars grown under different irrigation and nitrogen regimes

Wheat (Triticum durum L.) yields in the semi-arid regions are limited by inadequate water supply late in the cropping season. Planning suitable irrigation strategy and nitrogen fertilization with the appropriate crop phenology will produce optimum grain yields. A 3-year experiment was conducted on deep, fairly drained clay soil, at Tal Amara Research Station in the central Bekaa Valley of Lebanon to investigate the response of durum wheat to supplemental irrigation (IRR) and nitrogen rate (NR). Three water supply levels (rainfed and two treatments irrigated at half and full soil water deficit) were coupled with three N fertilization rates (100, 150 and 200 kg N ha⁻¹) and two cultivars (Waha and Haurani) under the same cropping practices (sowing date, seeding rate, row space and seeding depth). Averaged across N treatments and years, rainfed treatment yielded 3.49 Mg ha⁻¹ and it was 25% and 28% less than half and full irrigation treatments, respectively, for Waha, while for Haurani the rainfed treatment yielded 3.21 Mg ha⁻¹, and it was 18% and 22% less than half and full irrigation, respectively. On the other hand, N fertilization of 150 and 200 kg N ha⁻¹ increased grain yield in Waha by 12% and 16%, respectively, in comparison with N fertilization of 100 kg N ha⁻¹, while for cultivar Haurani the increases were 24% and 38%, respectively. Regardless of cultivar, results showed that supplemental irrigation significantly increased grain number per square meter and grain weight with respect to the rainfed treatment, while nitrogen fertilization was observed to have significant effects only on grain number per square meter. Moreover, results showed that grain yield for cultivar Haurani was less affected by supplemental irrigation and more affected by nitrogen fertilization than cultivar Waha in all years. However, cultivar effects were of lower magnitude compared with those of irrigation and nitrogen. We conclude that optimum yield was produced for both cultivars at 50% of soil water deficit as supplemental irrigation and N rate of 150 kg N ha⁻¹. However, Harvest index (HI) and water use efficiency (WUE) in both cultivars were not significantly affected neither by supplemental irrigation nor by nitrogen rate. Evapotranspiration (ET) of rainfed wheat ranged from 300 to 400 mm, while irrigated wheat had seasonal ET ranging from 450 to 650 mm. On the other hand, irrigation treatments significantly affected ET after normalizing for vapor pressure deficit (ET/VPD) during the growing season. Supplemental irrigation at 50% and 100% of soil water deficit had approximately 26 and 52 mm mbar⁻¹ more ET/VPD, respectively, than those grown under rainfed conditions.     

Irrigation strategies to improve the water use efficiency of wheat-maize double cropping systems in North China Plain

Water is the most important limiting factor of wheat (Triticum aestivum L.) and maize (Zea mays L.) double cropping systems in the North China Plain (NCP). A two-year experiment with four irrigation levels based on crop growth stages was used to calibrate and validate RZWQM2, a hybrid model that combines the Root Zone Water Quality Model (RZWQM) and DSSAT4.0. The calibrated model was then used to investigate various irrigation strategies for high yield and water use efficiency (WUE) using weather data from 1961 to 1999. The model simulated soil moisture, crop yield, above-ground biomass and WUE in responses to irrigation schedules well, with root mean square errors (RMSEs) of 0.029 cm³ cm⁻³, 0.59 Mg ha⁻¹, 2.05 Mg ha⁻¹, and 0.19 kg m⁻³, respectively, for wheat; and 0.027 cm³ cm⁻³, 0.71 Mg ha⁻¹, 1.51 Mg ha⁻¹ and 0.35 kg m⁻³, respectively, for maize. WUE increased with the amount of irrigation applied during the dry growing season of 2001-2002, but was less sensitive to irrigation during the wet season of 2002-2003. Long-term simulation using weather data from 1961 to 1999 showed that initial soil water at planting was adequate (at 82% of crop available water) for wheat establishment due to the high rainfall during the previous maize season. Preseason irrigation for wheat commonly practiced by local farmers should be postponed to the most sensitive growth stage (stem extension) for higher yield and WUE in the area. Preseason irrigation for maize is needed in 40% of the years. With limited irrigation available (100, 150, 200, or 250 mm per year), 80% of the water allocated to the critical wheat growth stages and 20% applied at maize planting achieved the highest WUE and the least water drainage overall for the two crops.     

Effects of irrigation water salinity and electrostatic water treatment for sugarcane production

Excess salinity in irrigation water reduces sugarcane yield and juice quality. This study was conducted to compare the effect of irrigation with water of 1.3 dS m⁻¹ vs. 3.4 dS m⁻¹ on sugarcane yield and quality, and to evaluate whether an electrostatic conditioning treatment of the water influenced the salt effects. The study was conducted in a commercial field divided into large plots ranging from 1.0 to 1.2 ha in size. Cane and sugar yields were reduced approximately 17% by the 3.4 dS m⁻¹ water compared to the 1.3 dS m⁻¹ water, but juice quality parameters were not affected. Conditioning of the irrigation water using a device called an ‘electrostatic precipitator’ which claimed to affect various water properties had no effect on cane yield, juice quality or soil salinity levels. The detrimental effect of the high salt irrigation water was somewhat less than might be expected, probably due to good late summer rainfall which may have flushed the root zone from the excessive salts.     

Yield and quality of melon grown under different irrigation and nitrogen rates

During 2 years, a melon crop (Cucumis melo L. cv. Sancho) was grown under field conditions to investigate the effects of different nitrogen (N) and irrigation (I) levels on fruit yield, fruit quality, irrigation water use efficiency (IWUE) and nitrogen applied efficiency (NAE). The statistical design was a split-plot with four replications, where irrigation was the main factor of variation and N was the secondary factor. In 2005, irrigation treatments consisted of applying daily a moderate water stress equivalent to 75% of ETc (crop evapotranspiration), a 100% ETc control and an excess irrigation of 125% ETc (designated as I₇₅, I₁₀₀ and I₁₂₅), while the N treatments were 30, 85, 112 and 139 kg N ha⁻¹ (designated as N₃₀, N₈₅, N₁₁₂ and N₁₃₉). In 2006, both the irrigation and N treatments applied were: 60, 100 and 140% ETc (I₆₀, I₁₀₀ and I₁₄₀) and 93, 243 and 393 kg N ha⁻¹ (N₉₃, N₂₄₃ and N₃₉₃). Moderate water stress did not reduce melon yield and high IWUE was obtained. Under severe deficit irrigation, the yield was reduced by 22% mainly due to decrease fruit weight. The relative yield (yield/maximum yield) was higher than 95% when the irrigation depth applied was in the range of 87-136% ETc. In 2006, the interaction between irrigation and N was significant for yield, fruit weight and IWUE. The best yield, 41.3 Mg ha⁻¹, was obtained with 100% ETc at N₉₃. The flesh firmness and the placenta and seeds weight increased when the irrigation level was reduced by 60% ETc. The highest NAE was obtained with quantities of water close to 100% ETc and increased as the N level was reduced. The highest IWUE was obtained with applications close to 90 kg N ha⁻¹. The I₂₄₃ and I₃₉₃ treatments produced inferior fruits due to higher skin ratios and lower flesh ratios. These results suggest that it is possible to apply moderate deficit irrigation, around 90% ETc, and reduce nitrogen input to 90 kg ha⁻¹ without lessening quality and yields.     

Yield and quality of two tomato (Solanum lycopersicum L.) cultivars as influenced by drip and furrow irrigation using waters having high residual sodium carbonate

Performance of tomato when irrigated with sodic waters particularly under drip irrigation is not well known. A field experiment was conducted for 3 years to study the response of tomato crop to sodic water irrigation on a sandy loam soil. Irrigation waters having 0, 5 and 10 mmol_c L⁻¹ residual sodium carbonate (RSC) were applied through drip and furrow irrigation to two tomato cultivars, Edkawi (a salt tolerant cultivar) and Punjab Chhuhara (PC). High RSC of irrigation water significantly increased soil pH, ECe and exchangeable sodium percentage progressively; the increases were higher in furrow compared to drip irrigation. Effect of high RSC on increasing bulk density and decreasing infiltration rate of soil was also pronounced in furrow-irrigated plots. Higher soil moisture and lower salinity near the plant was maintained under drip irrigation than under furrow irrigation. Performance of the two cultivars was significantly different; pooled over 2002–03 and 2003–04 seasons, PC yielded 38.8 and 30.0 Mg ha⁻¹ and Edkawi yielded 31.8 and 22.9 Mg ha⁻¹ under drip and furrow irrigation, respectively. At RSC10, cultivar PC produced 38 and 46% higher fruit yield than cultivar Edkawi under drip and furrow irrigation, respectively. Reduction in fruit yield at higher RSC was due to lower fruit weight under drip irrigation and due to reduced fruit number as well as fruit weight under furrow irrigation. Decrease in fruit weight was more pronounced in cultivar Edkawi than in cultivar PC. Increase in RSC lowered quality of the fruits except the ascorbic acid content. High RSC under drip irrigation, in general, had lesser deteriorating effect on the fruit quality particularly for cultivar PC than under furrow irrigation. For obtaining high tomato yield and better-quality fruits using high RSC sodic waters, drip irrigation should be preferred over furrow irrigation. Better performance of local cultivar PC compared to Edkawi at medium and high RSC suggests that cultivars categorized as tolerant to salinity should be evaluated in the sodic environment particularly when irrigated with high RSC sodic waters.     

Tuber yield, water and fertilizer productivity in early potato as affected by a combination of irrigation and fertilization

Excessive amounts of irrigation water and fertilizers are often utilized for early potato cultivation in the Mediterranean basin. Given that water is expensive and limited in the semi-arid areas and that fertilizers above a threshold level often prove inefficacious for production purposes but still risk nitrate and phosphorous pollution of groundwater, it is crucial to provide an adequate irrigation and fertilization management. With the aim of achieving an appropriate combination of irrigation water and nutrient application in cultivation management of a potato crop in a Mediterranean environment, a 2-year experiment was conducted in Sicily (South Italy). The combined effects of 3 levels of irrigation (irrigation only at plant emergence, 50% and 100% of the maximum evapotranspiration - ETM) and 3 levels of mineral fertilization (low: 50, 25 and 75 kg ha⁻¹, medium: 100, 50 and 150 kg ha⁻¹ and high: 300, 100 and 450 kg ha⁻¹ of N, P₂O₅ and K₂O) were studied on the tuber yield and yield components, on both water irrigation and fertilizer productivity and on the plant source/sink (canopy/tubers dry weight) ratio. The results show a marked interaction between level of irrigation and level of fertilization on tuber yield, on Irrigation Water Productivity and on fertilizer productivity of the potato crop. We found that the treatments based on 50% ETM and a medium level of fertilization represent a valid compromise in early potato cultivation management. Compared to the high combination levels of irrigation and fertilization, this treatment entails a negligible reduction in tuber yield to save 90 mm ha⁻¹ year⁻¹ of irrigation water and 200, 50 and 300 kg ha⁻¹ year⁻¹ of N, P₂O₅ and K₂O, respectively, with notable economic savings for farmers compared to the spendings that are usually made.     

Use of saline aquaculture wastewater to irrigate salt-tolerant Jerusalem artichoke and sunflower in semiarid coastal zones of China

In 2004 and 2005, the feasibility of agricultural use of saline aquaculture wastewater for irrigation of Jerusalem artichoke and sunflower was conducted in the Laizhou region using saline aquaculture wastewater mixed with brackish groundwater at different ratios. Six treatments with different electrical conductivities (EC) were included in the experiment: CK1 (rainfed), CK2 (irrigation with freshwater, EC of 0.02 dS m⁻¹), and saline aquaculture wastewater (EC of 39.2 dS m⁻¹) mixed with brackish groundwater (EC of 4.4 dS m⁻¹) at volumetric ratios of 1:1, 1:2, 1:3, and 1:4 with corresponding EC of 22.0, 16.1, 13.2, and 11.4 dS m⁻¹. Soil electrical conductivity (ECe) in the saline aquaculture wastewater irrigation treatments was significantly higher (P ≤ 0.05) than that in the rainfed or freshwater irrigation treatments, and the maximum value occurred in the 22.0 dS m⁻¹ treatment. The sodium adsorption ratio (SAR) ranged from 4.1 to 11.7 mmol^1/2 L^−1/2 and increased with decreasing salinity of irrigation water. The biomass of Jerusalem artichoke significantly decreased (P ≤ 0.05) when irrigated with saline aquaculture wastewater compared to the rainfed or freshwater irrigation treatments; however, the effect of salinity on root biomass was much smaller than the aerial parts. Concomitantly, the highest tuber yield of Jerusalem artichoke occurred in the 11.4 dS m⁻¹ treatment, while the highest seed yield of sunflower occurred in the rainfed treatment. Additionally, nitrogen and phosphorus concentrations of Jerusalem artichoke were significantly higher in the 11.4 dS m⁻¹ treatment than the other treatments. This study demonstrated that properly diluted saline aquaculture wastewater can be used successfully to irrigate Jerusalem artichoke with higher economic yield and nutrient removal, but not sunflower due to the difference in salt tolerance.     

Corn crop response under managing different irrigation and salinity levels

Non-uniformity of water distribution under irrigation system creates both deficit and surplus irrigation areas. Water salinity can be hazard on crop production; however, there is little information on the interaction of irrigation and salinity conditions on corn (Zea Mays) growth and production. This study evaluated the effect of salinity and irrigation levels on growth and yield of corn grown in the arid area of Egypt. A field experiment was conducted using corn grown in northern Egypt at Quesina, Menofia in 2009 summer season to evaluate amount of water applied, salinity hazard and their interactions. Three salinity levels and five irrigation treatments were arranged in a randomized split-plot design with salinity treatments as main plots and irrigation rates within salinity treatments. Salinity treatments were to apply fresh water (0.89 dS m⁻¹), saline water (4.73 dS m⁻¹), or mixing fresh plus saline water (2.81 dS m⁻¹). Irrigation treatments were a ratio of crop evapotranspiration (ET) as: 0.6ET, 0.8ET, 1.0ET, 1.2ET, and 1.4ET. In well-watered conditions (1.0ET), seasonal water usable by corn was 453, 423, and 380 mm for 0.89EC, 2.81EC and 4.73EC over the 122-day growing season, respectively. Soil salt accumulation was significantly increased by either irrigation salinity increase or amount decrease. But, soil infiltration was significantly decreased by either salinity level or its interaction with irrigation amount. Leaf temperature, transpiration rate, and stomata resistance were significantly affected by both irrigation and salinity levels with interaction. Leaf area index, harvest index, and yield were the greatest when fresh and adequate irrigation was applied. Grain yield was significantly affected in a linear relationship (r² ≥ 0.95) by either irrigation or salinity conditions with no interaction. An optimal irrigation scheduling was statistically developed based on crop response for a given salinity level to extrapolate data from the small experiment (uniform condition) to big field (non-uniformity condition) under the experiment constraints.     

Effects of salinity and fertigation practice on cotton yield and N recovery

The purpose of optimal water and nutrient management is to maximize water and fertilizer use efficiency and crop production, and to minimize groundwater pollution. In this study, field experiments were conducted to investigate the effect of soil salinity and N fertigation strategy on plant growth, N uptake, as well as plant and soil ¹⁵N recovery. The experimental design was a 3 × 3 factorial with three soil salinity levels (2.5, 6.3, and 10.8 dS m⁻¹) and three N fertigation strategies (N applied at the beginning, end, and in the middle of an irrigation cycle). Seed cotton yield, dry matter, N uptake, and plant ¹⁵N recovery significantly increased as soil salinity level increased from 2.5 to 6.3 dS m⁻¹, but they decreased markedly at higher soil salinity of 10.8 dS m⁻¹. Soil ¹⁵N recovery was higher under soil salinity of 10.8 dS m⁻¹ than those under soil salinity of 6.3 dS m⁻¹, but was not significantly different from that under soil salinity of 2.5 dS m⁻¹. The fertigation strategy that nitrogen applied at the beginning of an irrigation cycle had the highest seed cotton yield and plant ¹⁵N recovery, but showed higher potential loss of fertilizer N from the root zone. While the fertigation strategy of applying N at the end of an irrigation cycle tended to avoid potential N loss from the root zone, it had the lowest cotton yield and nitrogen use efficiency. Total ¹⁵N recovery was not significantly affected by soil salinity, fertigation strategy, and their interaction. These results suggest that applying nitrogen at the beginning of an irrigation cycle has an advantage on promoting yield and fertilizer use efficiency, therefore, is an agronomically efficient way to provide cotton with fertilizer N under the given production conditions.     

The effects of irrigation methods with effluent and irrigation scheduling on water use efficiency and corn yields in an arid region

A great challenge for the agricultural sector is to produce more food from less water, particularly in arid and semi-arid regions which suffer from water scarcity. A study was conducted to evaluate the effect of three irrigation methods, using effluent versus fresh water, on water savings, yields and irrigation water use efficiency (IWUE). The irrigation scheduling was based on soil moisture and rooting depth monitoring. The experimental design was a split plot with three main treatments, namely subsurface drip (SSD), surface drip (SD) and furrow irrigation (FI) and two sub-treatments effluent and fresh water, which were applied with three replications. The experiment was conducted at the Marvdasht city (Southern Iran) wastewater treatment plant during 2005 and 2006. The experimental results indicated that the average water applied in the irrigation treatments with monitoring was much less than that using the conventional irrigation method (using furrows but based on a constant irrigation interval, without moisture monitoring). The maximum water saving was obtained using SSD with 5907 m³ ha⁻¹ water applied, and the minimum water saving was obtained using FI with 6822 m³ ha⁻¹. The predicted irrigation water requirements using the Penman-Monteith equation (considering 85% irrigation efficiency for the FI method) was 10,743 m³ ha⁻¹. The pressure irrigation systems (SSD and SD) led to a greater yield compared to the surface method (FI). The highest yield (12.11 × 10³ kg ha⁻¹) was obtained with SSD and the lowest was obtained with the FI method (9.75 × 10³ kg ha⁻¹). The irrigation methods indicated a highly significant difference in irrigation water use efficiency. The maximum IWUE was obtained with the SSD (2.12 kg m⁻³) and the minimum was obtained with the FI method (1.43 kg m⁻³). Irrigation with effluent led to a greater IWUE compared to fresh water, but the difference was not statistically significant.     

Drip irrigation of tea (Camellia sinensis L.): 1. Yield and crop water productivity responses to irrigation

The effects of drip irrigation on the yield and crop water productivity responses of four tea (Camellia sinensis (L.) O. Kuntze) clones were studied four consecutive years (2003/2004-2006/2007), in a large (9 ha) field experiment comprising of six drip irrigation treatments (labelled: I₁-I₆) and four clones (TRFCA PC81, AHP S15/10, BBK35 and BBT207) planted at a spacing of 1.20 m × 0.60 m at Kibena Tea Limited (KTL), Njombe in the Southern Tanzania in a situation of limited water availability. Each clone × drip irrigation treatment combination was replicated six times in a completely randomized design with 144 net plots each with an area of 72 m². Clone TRFCA PC81 gave the highest yields (range: 5920-6850 kg dried tea ha⁻¹) followed by clones BBT207 (5010-5940 kg dried tea ha⁻¹), AHP S15/10 (4230-5450 kg dried tea ha⁻¹) and BBK35 (3410-4390 kg dried tea ha⁻¹) and drip irrigation treatment I₂ gave the highest yields, ranging from 4954 to 6072 kg dried tea ha⁻¹) compared with those from other treatments (4113-5868 kg dried tea ha⁻¹). Most of these yields exceeded those (4200 kg dried tea ha⁻¹) obtained from overhead sprinkler irrigation system in Mufindi also Southern Tanzania, and Kibena Estate itself. Results showed that drip irrigation of tea not only increased yields but also gave water saving benefits of up to 50% from application of 50% less water to remove the cumulative soil water deficit (treatment I₂), and with labour saving of 85% for irrigation. The yield of dried tea per mm depth of water applied, i.e., “the crop water productivity” for drip irrigation of clones TRFCA PC81, BBT207 and BBK35, in 2003/2004 for instance, were 9.3, 8.5 and 7.1 kg dried tea [ha mm]⁻¹, respectively. The corresponding values in 2004/2005 were 2.7, 4.5 and 2.0 kg dried tea [ha mm]⁻¹ while the yield responses from clone AHP S15/10 were linear decreasing by 1 and 1.6 kg dried tea [ha mm]⁻¹ in 2003/2004 and 2004/2005, respectively. In 2005/2006 the crop water productivity from clones TRFCA PC81, AHP S15/10, BBK35 and BBT207 were 4.5, 0.4, 5.2 and 6.9 kg dried tea [ha mm]⁻¹, respectively with quadratic yield response functions to drip irrigation depth of water application. The results are presented and recommendations and implications made for technology-transfer scaling-up for increased use by large and smallholder tea growers.     

Runoff nitrogen from a large sized paddy field during a crop period

Nutrient load management is an important environmental issue because nutrient loads from farmlands degrade surface waters as a result of anthropogenic eutrophication. Nitrogen load from a large sized paddy field during the crop period was examined from the results of field measurements carried out in 2004. The 1.5 ha paddy field was located east of Biwa Lake. Irrigation water volume and ponded water depth were continuously observed. Field measurements were carried out at least once a week to analyze total nitrogen (TN) concentration in the irrigation water and ponded water. Daily inflow and outflow of nitrogen was obtained by multiplication of the nitrogen concentration and transported water volume, consisting of irrigation, precipitation, evapotranspiration, percolation and surface discharge. Water outflow volume was calculated by a tank model that consisted of three small tanks connected to represent ponded water depth differences in the large paddy field. The calculated nitrogen load was 18.8 kg ha⁻¹, with 7.2 kg ha⁻¹ from surface drainage and 11.6 kg ha⁻¹ from percolation loss. The runoff nitrogen value of 18.8 kg ha⁻¹ was within the range of the reported values investigated in a medium-sized paddy field. The observed value was close to the value for a low percolation flux paddy field where less irrigation water has been applied. These results suggest that less irrigation water keep runoff nitrogen low. This also indicates that irrigation water management can reduce nitrogen load from large sized paddy fields.     

Long term responses of olive trees to salinity

Water demand for irrigation is increasing in olive orchards due to enhanced yields and profits. Because olive trees are considered moderately tolerant to salinity, irrigation water with salt concentrations that can be harmful for many of fruit tree crops is often used without considering the possible negative effects on olive tree growth and yield. We studied salt effects in mature olive trees in a long term field experiment (1998-2006). Eighteen-year-old olive trees (Olea europaea L.) cv. Picual were cultivated under drip irrigation with saline water composed of a mixture of NaCl and CaCl₂. Three irrigation regimes (i. no irrigation; ii. water application considering soil water reserves, short irrigation; iii. water application without considering soil water reserves and adding a 20% more as a leaching fraction, long irrigation) and three salt concentrations (0.5, 5 or 10 dS m⁻¹) were applied. Treatments were the result of the combination of three salt concentrations with two irrigation regimes, plus the non-irrigated treatment. Growth parameters, leaf and fruit nutrition, yield, oil content and fruit characteristics were annually studied. Annual leaf nutrient analyses indicate that all nutrients were within the adequate levels. After 8 years of treatment, salinity did not affect any growth measurement and leaf Na⁺ and Cl⁻ concentration were always below the toxicity threshold of 0.2 and 0.5%, respectively. Annual and accumulated yield, fruit size and pulp:stone ratio were also not affected by salts. However, oil content increased linearly with salinity, in most of the years studied. Soil salinity measurements showed that there was no accumulation of salts in the upper 30 cm of the soil (where most of the roots are present) because of leaching by rainfall at the end of the irrigation period. Results suggest that a proper management of saline water, supplying Ca²⁺ to the irrigation water, using drip irrigation until winter rest and seasonal rainfall typical of the Mediterranean climate leach the salts from the first 0-60 cm depth, and growing a tolerant cultivar, can allow using high saline irrigation water (up to 10 dS m⁻¹) for a long time without affecting growth and yield in olive trees.     

Treated sewage effluent as a source of water and nitrogen for Tifton 85 bermudagrass

The use of treated sewage effluent in agriculture has been a current practice in several countries. However, in Brazil, there are few studies about this subject. This research work aimed at evaluating the potential utilization of secondary-treated sewage effluent (STSE) as an alternative source of water and nitrogen (N) for Tifton 85 bermudagrass pasture. A field experiment was carried out at Lins, State of São Paulo, Brazil, for 2 years, using a randomized complete block design, with four replications and five treatments, as follows: (i) T1 (control) – irrigation with potable water and addition of mineral-N fertilizer (MNF) – 520 kg N ha⁻¹ year⁻¹; (ii) T2–T5 – irrigation with STSE (31.9 mg total-N L⁻¹) and addition of MNF – 0, 171.6, 343.2 and 520 kg N ha⁻¹ year⁻¹, respectively. Potable water and STSE characteristics were monitored monthly; above ground grass dry matter yield (DM) and crude protein content (CP) were determined bimonthly. Increases in DM and CP were observed for the high MNF rates associated with irrigation with STSE. STSE irrigation can efficiently substitute potable water for irrigation of Tifton 85 bermudagrass pasture and, simultaneously, save 32.2–81.0% of the recommended N rate without loss of grass DM and CP yield.     

Evaluating salinity distribution in soil irrigated with saline water in arid regions of northwest China

In arid and semi-arid regions, salinity is a serious and chronic problem for agriculture. A 3-year field experiment in the arid environment of Xinjiang, northwest China, was conducted to study the salinity change in soil resulting from deficit irrigation of cotton with non-saline, moderate saline and high saline water. The salinity profile distribution was also evaluated by an integrated water, salinity, and nitrogen model, ENVIRO-GRO. The simulated and observed salinity distributions matched well. Results indicated that after 3 years of cotton production, the average salinity in the 1.0-m soil profile was 336% and 547% of the original soil profile, respectively, for moderate saline and high saline water irrigation. If the practices continued, the average soil salinity (EC_e) in the 1.0-m soil profile would approach a steady level of 1.7, 10.8, and 14.7 dS m⁻¹, respectively, for the treatments receiving irrigation waters of 0.33, 3.62, and 6.71 dS m⁻¹. It was concluded that deficit irrigation of saline water in this region was not sustainable. Model simulation showed that a big flood irrigation after harvest can significantly reduce the salt accumulation in the soil profile, and that this practice was much more efficient for salinity control than applying the same extra amount of water during the growing season.