Irrigation frequency and amount affect yield components of summer squash (Cucurbita pepo L.)

The aim of this study carried out in Van, Turkey was to determine the most suitable irrigation frequencies and quantities in summer squash (Cucurbita pepo L. cv. Sakız) grown under field conditions. Irrigation quantities were based on pan evaporation (E_pan) from a screened class-A pan. Irrigation treatments consisted of two irrigation intervals (I1: 5 days; I2: 10 days), and three pan coefficients (K_cp1: 0.45; K_cp2: 0.65 and K_cp3: 0.85). Plants were adequately watered from seed sowing to first fruit emergence, then, scheduled irrigations were initiated at 5- and 10-day intervals.Irrigation quantities applied to the treatments varied from 279 to 475 mm; seasonal plant water consumption or evapotranspiration (E_t) of irrigation treatments varied from 336 to 539 mm; and the summer squash yield varied from 22.4 to 44.7 t ha⁻¹. The highest total yield was obtained from I1K_cp3 treatment. However, K_cp2 treatments had the earliest yield. Treatments irrigated with higher amount of water generally gave lower irrigation water use efficiency (IWUE) values than others. E_t/E_pan ratios of treatments ranged from 0.12 to 1.16. Moreover, irrigation treatments had significant effects (P<0.01) on yield and there were significant positive linear relations among irrigation water, plant water consumption, fruit traits and yield.In conclusion, K_cp3 treatment with 5-day irrigation interval is recommended for summer squash grown under field conditions in order to get higher summer squash yield. However, if the irrigation water is scarce, it will be suitable to irrigate summer squash frequently using K_cp1 values.     

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.     

Effect of irrigation method and quantity on squash yield and quality

Squash yield and quality under furrow and trickle irrigation methods and their responses to different irrigation quantities were evaluated in 2010 spring and fall growing seasons. A field experiment was conducted using squash (Cucurbita pepo L.) grown in northern Egypt at Shibin El Kom, Menofia. A randomized split-plot design was used with irrigation methods as main plots and different irrigation quantities randomly distributed within either furrow or trickle irrigation methods. Irrigation quantity was a fraction of crop evapotranspiration (ET_c) as: 0.5, 0.75, 1.0, 1.25, and 1.5 ET_c. Each treatment was repeated three times, two of five rows from each replicate were left for squash seed production. In well-watered conditions (1.0 ET_c), seasonal water use by squash was 304 and 344 mm over 93 days in spring and 238 and 272 mm over 101 days in fall under trickle and furrow irrigation methods, respectively. Squash fruit yield and quality were significantly affected by season and both irrigation method and quantity. Fruit number and length were not affected by irrigation method and growing season, respectively. Interaction between season and irrigation quantity significantly affected leaf area index, total soluble solid (TSS), and fruit weight. Moreover, seed yield and quality were significantly affected by growing season and both irrigation method and quantity except harvest index, which was not affected by irrigation method. Significant differences for the interaction between season and irrigation method were only found for seed yield and 100 seeds weight. Except for harvest index, no significant difference was observed by interaction between season and irrigation quantity. Both fruit and seed yields were significantly affected in a linear relationship (r² ≥ 0.91) by either deficit or surplus irrigation quantities under both irrigation methods. Adequate irrigation quantity under trickle irrigation, relative to that of furrow, enhanced squash yield and improved its quality in both growing seasons. Fall growing season was not appropriate for seed production due to obtaining many of empty seeds caused by low weather variables at the end of the season. The results from small experiment were extrapolated to large field to find out optimal irrigation scheduling under non-uniform of irrigation application.     

灌水模式及下限对滴灌棉花产量和品质的影响

为探索滴灌条件下棉花优质高效灌溉指标,在新疆石河子研究了地下滴灌(SSDI)和膜下滴灌(SDI)条件下不同灌水控制下限对棉花耗水量、品质以及水分利用率的影响.结果表明,相同滴灌模式,棉花蕾期耗水量随灌水控制下限的提高而增加,花铃期水分胁迫处理的棉花阶段耗水量普遍低于对照处理;蕾期适度水分胁迫(灌水控制下限为60% FC)花铃期充分供水(灌水控制下限为75% FC)处理(SDI-7和SSDI-7)有利于籽棉产量的提高,与对照处理相比,籽棉产量提高了14.48%(SDI-7)和11.60%(SSDI-7);水分处理对棉花衣分、棉纤维整齐度的影响不明显,蕾期和花铃期水分胁迫对棉纤维上半部平均长度的影响随水分胁迫程度的加重而加剧,蕾期适度水分胁迫(灌水控制下限为60% FC)有利于棉纤维断裂比强度的提高.相同水分处理,地下滴灌棉花产量和灌溉水利用率均高于膜下滴灌棉花.与对照处理相比,蕾期和花铃期灌水控制下限分别为60% FC和75% FC,灌水定额为30 mm处理在节约灌溉水的同时提高了籽棉产量并改善了棉纤维品质,可作为石河子垦区滴灌棉花适宜的灌水指标.     

Effect of amount and timing of subsurface drip irrigation on corn yield

A field study was conducted at North Platte, Nebraska in 2007–2009, imposing eight irrigation treatments, ranging from dryland to fully irrigated. Four of the eight treatments allowed for various degrees of water stress only after tasseling and silking. In 2007, corn yield ranged from 8.9 Mg ha^?1 with a season total of 41 mm of irrigation water to 11.5 Mg ha^?1 for the fully irrigated treatment (264 mm of irrigation water). The treatment with the greatest reduction in irrigation water after tasseling and silking (158 mm) had a mean yield of 10.9 Mg ha^?1, only 0.6 Mg ha^?1 less than the fully irrigated treatment. In 2009, yields ranged from 12.6 to 13.5 Mg ha^?1. There were no significant yield differences between the irrigation treatments for several possible reasons: more in-season precipitation and cooler weather required less irrigation water; much of the irrigation water was applied after the most water-stress sensitive stages of tasseling and silking; and lower atmospheric demand allowed for soil water contents well below 50 % management allowed depletion (MAD) not to cause any yield losses.     

Effect of irrigation amounts applied with subsurface drip irrigation on corn evapotranspiration, yield, water use efficiency, and dry matter production in a semiarid climate

Quantifying the local crop response to irrigation is important for establishing adequate irrigation management strategies. This study evaluated the effect of irrigation applied with subsurface drip irrigation on field corn (Zea mays L.) evapotranspiration (ETc), yield, water use efficiencies (WUE = yield/ETc, and IWUE = yield/irrigation), and dry matter production in the semiarid climate of west central Nebraska. Eight treatments were imposed with irrigation amounts ranging from 53 to 356 mm in 2005 and from 22 to 226 mm in 2006. A soil water balance approach (based on FAO-56) was used to estimate daily soil water and ETc. Treatments resulted in seasonal ETc of 580–663 mm and 466–656 mm in 2005 and 2006, respectively. Yields among treatments differed by as much as 22% in 2005 and 52% in 2006. In both seasons, irrigation significantly affected yields, which increased with irrigation up to a point where irrigation became excessive. Distinct relationships were obtained each season. Yields increased linearly with seasonal ETc (R² = 0.89) and ETc/ETp (R² = 0.87) (ETp = ETc with no water stress). The yield response factor (ky), which indicates the relative reduction in yield to relative reduction in ETc, averaged 1.58 over the two seasons. WUE increased non-linearly with seasonal ETc and with yield. WUE was more sensitive to irrigation during the drier 2006 season, compared with 2005. Both seasons, IWUE decreased sharply with irrigation. Irrigation significantly affected dry matter production and partitioning into the different plant components (grain, cob, and stover). On average, the grain accounted for the majority of the above-ground plant dry mass (≈59%), followed by the stover (≈33%) and the cob (≈8%). The dry mass of the plant and that of each plant component tended to increase with seasonal ETc. The good relationships obtained in the study between crop performance indicators and seasonal ETc demonstrate that accurate estimates of ETc on a daily and seasonal basis can be valuable for making tactical in-season irrigation management decisions and for strategic irrigation planning and management.     

Growth and yield of oleic sunflower (Helianthus annuus L.) under drip irrigation in very strongly saline soils

A four-year trial was set up to test the feasibility of growing oleic sunflower in a very strongly saline wasteland with drip irrigation in the Ningxia plain of Northwest China. The soil salinity expressed as electrical conductivity of the saturation paste extract (EC _e ) was around 28 dS/m, and soil nutrient was deficient in the upper 120 cm depth. The experiment included five soil matric potential (SMP) treatments, with the SMP at 20-cm depth immediately under the emitters maintained to be higher than ?5, ?10, ?15, ?20 and ?25 kPa after sunflower establishment. Drip irrigation consistently created a favourable soil moisture and low-salinity region in the root zone when the SMP was maintained higher than ?25 kPa. The sunflower dry seed yield decreased by 3.8 % for each unit increase in seasonal average soil salinity in the root zone. Plant vegetative growth, yield characteristics, irrigation frequency and irrigation amount all increased with the increase in SMP from ?25 to ?5 kPa, and the highest irrigation water use efficiency was available when the SMP was between ?10 and ?15 kPa (the amount of applied water was around 750 mm). Leaching of salts by drip irrigation gradually turned the very strongly saline soil into a moderately saline soil. This research suggests that drip irrigation can be successfully used in oleic sunflower cultivation in this highly saline soil and a SMP threshold between ?10 and ?15 kPa is suggested for irrigation scheduling.     

Effect of N-enriched co-compost on transpiration efficiency and water-use efficiency of maize (Zea mays L.) under controlled irrigation

Population growth, urban expansion and economic development are increasing competition for water use between agriculture and other users. In addition, the high rate of soil degradation and declining soil moisture in the Sub-Saharan African Region have called for several crop production management and irrigation options to improve soil fertility, reduce water use by crops and produce ‘more crops per drop of water’. Notwithstanding this, considerable variations exist in the literature on water-use efficiency, WUE_cwu (economic yield per water used) for maize (Zea mays L.) across climates and soil management practices. Different views have been expressed on the effect of different rates of nitrogen (N) application on transpiration efficiency, TE (biomass produced per unit of water transpired). The objectives of the study were to assess the effect of different rates of N-enriched municipal waste co-compost and its derivatives on TE, WUE_cwu and yield of maize (Z. mays L.) in comparison to inorganic fertiliser. The greenhouse pot experiment was conducted in Accra, Ghana on a sandy loam soil (Ferric Lixisol) using a split plot design. The main plot treatments were soil (S), dewatered faecal sludge (DFS), municipal solid waste compost (C), co-compost from municipal solid waste and dewatered faecal sludge (Co), compost enriched with (NH₄)₂SO₄ (EC), co-compost enriched with (NH₄)₂SO₄ (ECO), (NH₄)₂SO₄ and NPK15-15-15 + (NH₄)₂SO₄. The sub-plot treatments were different rates of application of nitrogen fertiliser applied at the rate of 91, 150 and 210 kg N ha⁻¹ respectively. Maize cv. Abelehii was grown in a poly bag filled with 15 kg soil. Eight plants per treatment were selected randomly and used for the collection of data on growth parameters forth-nightly. At physiological maturity two plants per treatment were also selected randomly from each treatment plot for yield data. The results showed that TE of maize (Z. mays) varied for the different treatments and these are 6.9 Pa in soil (S) alone to 8.6 Pa in ECO. Increase in N application rate increased TE at the vegetative phase for fast nutrient releasing fertilisers (DFS, ECO, EC, NPK + (NH₄)₂SO₄, (NH₄)₂SO₄) and at the reproductive phase for slow nutrient releasing fertilisers (C and CO). Water-use efficiency increased significantly as rate of N application increased. Treatment ECO improved crop WUE_cwu and was 11% and 4 times higher than that for NPK + (NH₄)₂SO₄ or soil alone; and 18-36% higher than those for DFS and CO. Treatment ECO used less amount of water to produce dry matter yield (DMY) and grain yield (GY) that was 5.2% and 12.6%, respectively, higher than NPK + (NH₄)₂SO₄. Similarly, the DMY and GY for ECO was 8.9-18.5% and 23.4-34.7%, respectively, higher than DFS and CO. High nutrient (N and K) uptake, TE, and low leaf senescence accounts for 83% of the variations in DMY whereas WUE_cwu accounts for 99% of the variations in GY. Thus, the study concluded that different sources of fertiliser increased TE and WUE_cwu of maize differently as N application rate increases.     

Effect of field levelling quality on irrigation efficiency and crop yield

Proper land levelling in areas irrigated by canals is an essential pre-requisite for judicious use of scarce irrigation water. The concept of land levelling index, which is different from land uniformity coefficient used hitherto, has been adopted to evaluate quantitatively the precision or quality of land levelling work. Using this concept the quality of land levelling work being done in newly canal commanded areas has been assessed and it is demonstrated that the prevalent deficiency in levelling quality ranges from 21.4 to 42.2%. Field investigations have been carried out to assess quantitatively the effect of land levelling quality on irrigation and water-use efficiencies and crop yield. The study comprised five levelling indices viz., 1.2, 2.0, 2.5, 3.0 and 3.7 cm and two irrigation treatments, i.e., fixed depth and complete irrigation. The results show that irrigation application, distribution, and water-use efficiency are appreciably reduced with increase in levelling index or deterioration in levelling quality. The wheat grain yield is also similarly reduced and it is significantly less for levelling index values higher than 2.5 cm. The fixed irrigation depth treatment gives better results from the point of water economy than does the complete irrigation treatment. From this study, it can be inferred that to obtain reasonably high yield and judicious use of water at a reasonable cost the field levelling index should not have a value greater than 3.0 cm.     

滴灌水氮耦合对水氮利用及冬小麦产量的影响

以华北地区冬小麦为试验对象,参考直径20 cm标准蒸发皿的累计水面蒸发量E,通过2 a的大田试验(2012—2013),研究了大田地表滴灌条件下水氮耦合制度对作物耗水量、作物生理指标、产量、氮残留及水氮利用效率的影响,结果表明,冬小麦生育期内的耗水量、叶面积指数及产量受灌水定额的影响更为显著(P<0.05);滴灌条件下,当施氮量在120~290 kg/hm²时,水氮耦合效应对冬小麦耗水量的影响不具有统计学意义;在滴灌灌水定额为0.80E,施氮量为140~190 kg/hm²的水氮耦合模式下,冬小麦的产量较高,土壤硝态氮的当季残留较少,且进一步显著增加灌水定额和氮肥投入量将导致产量的明显下降;综合考虑冬小麦水氮利用效率和对地下水的潜在淋失风险,华北典型区滴灌水氮耦合的优化组合范围宜为灌水定额为0.80E,施氮量为140~190 kg/hm².     

干旱区秸秆覆盖对滴灌棉花生长及产量的影响

为探索秸秆覆盖对北疆滴灌棉花生长特征和产量的影响,2009—2012年期间,以小麦秸秆为材料,在非盐碱土和盐碱土2种土壤条件下,进行了无覆盖（LUM）、表层覆盖（LSM）、地表以下30 cm深处覆盖（LM30）的测坑对比试验.结果表明：秸秆覆盖对棉花生长及产量具有一定的促进效果,对盐碱土种植的棉花株高、叶面积指数和产量的促进作用显著,而对非盐碱土棉花株高、叶面积指数和产量的促进作用不明显.地表覆盖综合调控效应优于30 cm深层覆盖,尤其是在棉花花铃期,在盐分抑制方面地表覆盖要比30 cm覆盖效果好;30 cm覆盖在苗期和蕾期可以给棉花生长创造比较好的条件,而在花铃期以后这种覆盖效果不太明显;表层覆盖处理棉花产量最高,高出无覆盖处理3.2%-17.9%,高出30 cm深层覆盖3.1%-16.3%.     

Response of lemongrass (Cymbopogon flexuosus) under different levels of irrigation on deep sandy soils

The growth and herbage and oil production of East Indian lemongrass (Cymbopogon flexuosus) in response to different levels of irrigation water (IW) [0.1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3 and 1.5 times cumulative pan evaporation (CPE)] were evaluated on deep sandy soils at the research farm of the Central Institute of Medicinal and Aromatic Plants, Lucknow, from 1991 to 1993. In general, an increment in the level of irrigation increased the plant height up to 0.7 IW:CPE ratio. The response of irrigation levels on tiller production of lemongrass differed with the season of harvest. Maximum tillers/clump during the 2nd, 3rd, 6th and 7th harvests were in response to irrigation levels 0.9, 0.5, 0.7 and 0.7 IW:CPE ratio, respectively. Oil content had an inverse relationship with the levels of irrigation, specially during the 1st, 2nd, 5th and 6th harvests. Significantly higher herb and essential oil yields were recorded at 0.7 IW:CPE ratio, irrespective of season of harvest. The maximum total herb (22.79 t/ha in first year and 33.11 t/ha in second year) and oil (146.2 l/ha in the first year and 205.3 l/ha in the second year) yields were recorded at 0.7 IW:CPE ratio. The quality of oil with respect to the major chemical constituents (Citral-a, Citral-b and geraniol) was not changed. At the optimum level of irrigation (0.7 IW:CPE ratio) the water used by lemongrass was 118.2 cm for first year and 123.8 cm for the second year. Water-use efficiency was found to be higher (1.66 l oil/ha-cm) in the second year than the first year (1.23 l oil/ha-cm). For optimum yield potential of lemongrass on deep sandy soils of sub-tropical climate, the crop received 17 irrigations in the first year and 14 irrigations in the second year of harvests. Irrigations were made during the dry winter and summer months. Received: 15 April 1999     

Effect of soil matric potential on tomato yield and water use under drip irrigation condition

Field experiment was carried out to investigate the effect of soil matric potential (SMP) on tomato yield, evapotranspiration (ET), water use efficiency (WUE) and irrigation water use efficiency (IWUE) under drip irrigation condition in North China Plain. The experiment included five treatments, which controlled SMP at 0.2 m depth immediately under drip emitter higher than −10 (S1), −20 (S2), −30 (S3), −40 (S4) and −50 kPa (S5), respectively, after tomato plant establishment. The results showed that different SMP affected irrigation amount and tomato ET. Irrigation amount decreased from 185 mm (S1) to 83.6 mm (S5) in 2004, and from 165 mm (S1) to 109 mm (S5) in 2005, respectively. The ET decreased from 270 mm (S1) to 202 mm (S5) in both years. However, it was found that SMP did not affect the tomato yield significantly, for the range of SMP investigated. Both WUE and IWUE increased as SMP decreased. The maximum WUE (253 and 217 kg/ha mm) and IWUE (620 and 406 kg/ha mm) were for S5 in 2 years, whereas the minimum WUE (178 and 155 kg/ha mm) and IWUE 261 and 259 kg/ha mm) were for S1 in 2004 and 2005. Based on the above results, therefore, it is recommended that if the tomatoes are well irrigated (SMP is higher than −20 kPa) during establishment, controlling SMP higher than −50 kPa at 0.2 m depth immediately under drip emitter can be used as an indicator for drip irrigation scheduling during following period of tomato growth in North China Plain.     

Effect of different drip irrigation regimes on sugar beet (Beta vulgaris L.) yield, quality and water use efficiency in Middle Anatolian, Turkey

Agricultural production has forced researchers to focus on increasing water use efficiency by improving either new drought-tolerant plant varieties or water management for arid and semi-arid areas under water shortage conditions. A field study was conducted to determine effects of seasonal deficit irrigation on plant root yield, quality and water use efficiency (WUE) of sugar beet for a 2-year period in the semi-arid region. Irrigations were applied when approximately 50–55% of the usable soil moisture was consumed in the effective rooting depth at the full irrigation (FI) treatment. In deficit irrigation treatments, irrigations were applied at the rates of 75, 50 and 25% of full irrigation treatment on the same day. Irrigation water was applied by a drip irrigation system. Increasing water deficits resulted in a relatively lower root and white sugar yields. The linear relationship between evapotranspiration and root yield was obtained. Similarly, WUE was the highest in DI25 irrigation conditions and the lowest in full irrigation conditions. According to the averaged values of 2 years, yield response factor (k _y ) was 0.93 for sugar beet. Sugar beet root quality parameters were influenced by drip irrigation levels in both years. The results revealed that irrigation of sugar beet with drip irrigation method at 75% level (DI25) had significant benefits in terms of saved irrigation water and large WUE, indicating a definitive advantage of deficit irrigation under limited water supply conditions. In an economic viewpoint, 25% saving of irrigation water (DI25) caused 6.1% reduction in the net income.     

黄河水滴灌对葡萄生长发育及产量品质的影响

为了探究引黄滴灌对大田葡萄生长发育以及产量品质的影响,以3 a生克伦生葡萄为供试材料,开展全生育期黄河水和地下水滴灌的大田对比试验,监测全生育期内2种水质滴灌处理条件下葡萄的各项指标,分析黄河水滴灌对葡萄生长、产量和品质的影响.结果发现：黄河水能显著影响克伦生葡萄生长发育、浆果外观品质以及果实营养物质含量,能促进新梢枝条生长发育、促进果实膨大、提高果形指数C和硬度P,葡萄可溶性固形物含量TSS和浆果可溶性糖含量WSS分别较地下水处理提高了21.26%和13.59%,Ta含量降低了15.79%.综合分析表明,黄河水滴灌对促进克伦生葡萄新梢枝条生长发育、提高葡萄产量和改善浆果营养品质具有积极意义.试验可为葡萄引黄滴灌发展提供科学依据和理论参考.     

Different drip irrigation regimes affect cotton yield, water use efficiency and fiber quality in western Turkey

Decreasing in water availability for cotton production has forced researchers to focus on increasing water use efficiency by improving either new drought-tolerant cotton varieties or water management. A field trial was conducted to observe the effects of different drip irrigation regimes on water use efficiencies (WUE) and fiber quality parameters produced from N-84 cotton variety in the Aegean region of Turkey during 2004 and 2005. Treatments were designated as full irrigation (T₁₀₀, which received 100% of the soil water depletion) and those that received 75, 50 and 25% of the amount received by treatment T₁₀₀ on the same day (treatments T₇₅; T₅₀ and T₂₅, respectively). The average seasonal water use values ranged from 265 to 753 mm and the average seed cotton yield varied from 2550 to 5760 kg ha⁻¹. Largest average cotton yield was obtained from the full irrigation treatment (T₁₀₀). WUE ranged from 0.77 kg m⁻³ in the T₁₀₀ to 0.98 kg m⁻³ in the T₂₅ in 2004 growing season and ranged from 0.76 kg m⁻³ in the T₁₀₀ to 0.94 kg m⁻³ in the T₂₅ in 2005 growing season. The largest irrigation water use efficiency (IWUE) was observed in the T₂₅ (1.46 kg m⁻³), and the smallest IWUE was in the T₁₀₀ treatment (0.81 kg m⁻³) in the experimental years. A yield response factor (k_y) value of 0.78 was determined based on averages of two years. Leaf area index (LAI) and dry matter yields (DM) increased with increasing water use for treatments. Fiber qualities were influenced by drip irrigation levels in both years. The results revealed that well-irrigated treatments (T₁₀₀) could be used for the semi-arid climatic conditions under no water shortage. Moreover, the results also demonstrated that irrigation of cotton with drip irrigation method at 75% level (T₇₅) had significant benefits in terms of saved irrigation water and large WUE indicating a definitive advantage of deficit irrigation under limited water supply conditions. In an economic viewpoint, 25.0% saving in irrigation water (T₇₅) resulted in 34.0% reduction in the net income. However, the net income of the T₁₀₀ treatment is found to be reasonable in areas with no water shortage.     

Effects of fixed partial root-zone drying irrigation and soil texture on water and solute dynamics in calcareous soils and corn yield

Water dynamics and salt distribution in the soil were studied under Fixed Partial Root zone Drying irrigation (FPRD) conditions in corn fields in Northern Greece. FPRD irrigation technique was applied without deficit treatment in two calcareous soils, a sandy clay loam and a sandy loam. Soil water content was recorded in the vertical profile of 0.6 m with the use of capacitance sensors in the row and interrow positions of plants. Salt built-up was monitored to the depth of the root zone, bi-weekly, by measuring electrical conductivity (EC_e) and the concentrations of soluble cations Ca²⁺, Mg²⁺, Na⁺ and K⁺ of the saturation extract on irrigated and non irrigated interrow positions. Soil moisture distribution and salt built-up in soil were used to evaluate the potentials and constraints of FPRD efficiency to sustain plant growth and crop production as a low cost drip irrigation technique. The results indicated that FPRD application on both soils was capable of supplying sufficient amounts of water on plant row. Soil analyses showed that salts accumulated to high levels in the soil surface and decreased in depth at the non irrigated interrow positions. Spatial and temporal variability of salt movement and distribution in the soil profile of 0.6 m were ascribed to soil textural differences. The development and yield of corn plants for both soils reached the usual standards for the area with a minor decrease in the sandy loam soil.     

Subsurface drip irrigation of onions: Effects of drip tape emitter spacing on yield and quality

Improved irrigation water use efficiency is an important component of sustainable agricultural production. Efficient water delivery systems such as subsurface drip irrigation (SDI) can contribute immensely towards improving crop water use efficiency and conserving water. However, critical management considerations such as choice of SDI tube, emitter spacing and installation depth are necessary to attain improved irrigation efficiencies and production benefits. In this study, we evaluated the effects of subsurface drip tape emitter spacing (15, 20 and 30 cm) on yield and quality of sweet onions grown at two locations in South Texas—Weslaco and Los Ebanos. Season-long cumulative crop evapotranspiration (ETc) was 513 mm in Weslaco and 407 mm at Los Ebanos. Total crop water input (rain + irrigation) at Weslaco was roughly equal to ETc (92% ETc) whereas at Los Ebanos, water inputs exceeded ETc by about 35%. Onion yields ranged from 58.5 to 70.3 t ha⁻¹ but were not affected by drip tube emitter spacing. Onion pungency (pyruvic acid development) and soluble solids concentration were also not significantly influenced by treatments. Crop water use efficiency was slightly higher at Weslaco (13.7 kg/m³) than at Los Ebanos (11.7 kg/m³) partly because of differences in total water inputs resulting from differences in irrigation management. The absence of any significant effects of drip tape emitter spacing on onion yield may be due to the fact that irrigation was managed to provide roughly similar irrigation amounts and optimum soil moisture conditions in all treatments.     

Effects of wastewater irrigation on soil sodicity and nutrient leaching in calcareous soils

Soil column studies were conducted with two soils to assess the effects of irrigation with wastewater on soil and groundwater quality. Upon the application of wastewater, exchange occurred between solution sodium (Na⁺) and exchangeable cations (Ca²⁺, Mg²⁺, K⁺), whereby these cations were released into solution. The average exchangeable sodium percentage (ESP) of the soils increased during leaching from 9 to 21 and 28.8 to 29.7 after applying 5.0 and 3.5 l (about 7 and 6 pore volumes) of wastewater to the soils columns, respectively. Adverse effect of high Na⁺ concentration in the wastewater on raising ESP was less pronounced in the soil having initial high ESP than in the soil with low initial ESP. Salinity of the soils was also increased with the application of wastewater and Mg²⁺ and K⁺ were leached from the soils. These losses would be more severe on soils having a low cation exchange capacity and if, uncorrected could lead eventually to their deficiencies for plant growth. When the soil columns were leached with distilled water the flow rate of one soil decreased to zero after 2.2 pore volume indicating damage to soil structure. Irrigation with wastewater, which is generally more sodic and saline than regional groundwater, increases the rate of soil sodification of shallow groundwater. A relatively simple chromatographic model was used to estimate final ESP profiles in the soils assuming the condition of local equilibrium. This approach had a limited success for one of the soil. Since the final leached concentrations are in good agreement with those of wastewater, we attribute these differences to non-uniform flow through the column. In terms of practical soil and water management, our study reveals that relatively simple means can be useful to predict the water quality in soils, their discharge to ground water, and the hazard of soil structure deterioration.