Pan Evaporation Replenishment Research Articles

Water production function and optimal irrigation programme for drip irrigated castor (Ricinus communis L.)

Water shortage for crop production necessitates adequate knowledge of the crop water production function to make decisions on water allocation for optimum returns from castor crop under surface drip irrigation. The study was conducted in rabi 2009-10 at Agricultural college farm, Rajendranagar, Hyderabad. The different drip irrigation schedules at 40, 60 and 80 per cent pan evaporation replenishment levels either kept constant throughout the crop life or combinations at vegetative, flowering and development stages were compared with surface check basin at (0.8 IW/CPE ratio) irrigation. The results showed that drip irrigation at 0.6 Epan replenishment up to flowering and 0.8 Epan later on registered comparable seed yields with drip irrigation scheduled at either at 0.6 or 0.8 Epan and was significantly superior over other treatments and the best fit water production function was quadratic (R2= 0.99). The optimum quantity of water (ETc) for maximum net returns under prevailing prices (water and castor @ `10 and 30 ha/mm and kg/ha, respectively) was 381.4 ha mm with a resultant seed yield of 3611 kg/ha. The gross returns, net returns and net return/rupee invested varied from ` 72194 to 144447/ha, ` 36808 to 108018/ha and 1.040 to 3.049, respectively.

Replacing conventional surface irrigation with micro-irrigation in vegetables can alleviate arsenic toxicity and improve water productivity

Arsenic (As), a heavy metal(loid), is exceedingly hazardous and carcinogenic and harms people, soil, plants, and water. Vegetable consumption can be a source for the absorption of As in humans. To find a feasible mitigation technique, a field experiment was conducted with broccoli (cv. Green Magic) and cauliflower (cv. Pusa Snowball) in geogenically arsenic-contaminated areas (West Bengal, India) for two consecutive years in a randomized block design replicated seven times with surface irrigation of 20 mm depth, gravity drip and sprinkler irrigation at 1.0 and 0.7 of pan evaporation replenishment. Results revealed that the lowest As accumulation in the edible heads was accomplished by micro-irrigation (0.34 and 0.31 mg kg−1) over the farmer's practice of surface irrigation (0.42 and 0.38 mg kg−1) for broccoli and cauliflower. Micro-irrigation improved the average head yield by 5.26 and 6.53%, weight by 6.37 and 3.06%, and diameter by 1.14 and 1.23% for broccoli and cauliflower respectively and also resulted in substantial water saving to an extent of 37.3%. Further reduction in As stress reduced the activity of antioxidant enzymes like catalase, superoxide dismutase and peroxidase; and reduced the dietary carcinogenic risk like Severity Adjusted Margin of Exposure (SAMOE) from moderate-high to low. Accordingly, drip irrigation without water stress can benefit vegetable growing in the As-contaminated regions based on the competitive advantage.

Effect of gravity-fed drip irrigation and nitrogen management on flowering quality, yield, water and nutrient dynamics of gladiolus in an Indian inceptisol

Gladiolus is a promising flower crop during winter season and its popularity is growing fast due to its higher price in the market. However, the productivity and quality of the crop in resource-scarce region are constrained by improper irrigation and nitrogen management practices. Based on this presumption, the current study has been developed with the precise objectives of examining the effect of gravity-fed drip irrigation scheduling coupled with integrated nitrogen management on growth, yield, water productivity and macronutrients distribution in soil and plant system of gladiolus. The field experiment accommodating four irrigation levels (surface irrigation I1, and gravity drip irrigation at 1.0, 0.8 and 0.6 (I2, I3 and I4) of pan evaporation replenishment) and three levels of nitrogen management (100% recommended dose of nitrogen (RDN) as vermicompost, 50% RDN as vermicompost + 50% RDN as fertilizer and 100% RDN as fertilizer, respectively N1, N2 and N3) was conducted during three consecutive rabi seasons on gladiolus. I2N2 furnished highest spike/plot (72.9), florets/spike (10.6), longest spike length (66.7 cm), greatest spike weight (43.0 g) and maximum spike yield (10458 kg ha−1) which were at par with I2N2. Highest crop water productivity (CWP) of 9.06 kg m−3 was accomplished in I4N2 followed by I3N2 (8.84 kg m−3). Drip irrigation, on average, could save water by 20.6% for I2, 36.6% for I3 and 52.4% for I4 and improve CWP by 50.2% for I2, 65.2% for I3 and 65.2% for I4 as compared with I1. Two predictive models were developed based on flower yield vs. I and ETa. Ky for total growing season was estimated at 0.66 (R2= 0.91). Maximum soil water storage was accumulated in the surface layer and well distributed down the layers underneath in drip irrigation system, while the reverse trend was noticed in the surface irrigation. Higher availability of soil N and leaf N concentrations were obtained with I2N2 and I3N2 and lower with I1N1. Based on maximum spike yield, water productivity, substantial water saving and N economy, I2N2 and I3N2 emerged superior for the selected inceptisol.

Standardization of stage wise water requirement in drip irrigated Kinnow mandarin orchards under sub-tropical conditions


 An experiment on drip irrigation scheduling based on pan evaporation replenishment was conducted in Kinnow orchard at Punjab Agricultural University, Ludhiana during 2010-2018. Year was divided into six stages (stage 1 to stage VI) including two months in each stage. First treatment included irrigation scheduling with 30 and 40% ER, treatment two with 40 and 60% ER, treatment three with 60 and 80% ER, alternatively during stages I to VI. However, fourth and fifth treatments had irrigation with 80% ER and 30% ER, respectively, in all the stages. Maximum daily open pan evaporation (9.15 mm) was recorded in May and minimum (1.19 mm) was recorded in January. The water requirement varied from 2.8 liters day-1 tree-1 in stage-I to 58.3 liters day-1 tree-1 in stage-III. Linear increase in vegetative and reproductive growth was observed with increase in irrigation water. Polynomial relationship studies indicated the increase in water quantity applied to Kinnow with increase in temperature subject to the prevailing relative humidity. Similarly, volumes of water applied increased with increased mean evaporation. The study concluded that drip irrigation scheduling with 60 to 80% ER alternatively, starting from January to December save significant amount of water, without affecting yield and quality of Kinnow under subtropical conditions.

Techno-economic evaluation of gravity fed drip irrigation and nitrogen nutrition on gladiolus in Gangetic alluvial plains of eastern India

Optimization of water and nitrogen is vital for gladiolus production. Field experiments were carried out during rabi seasons of 2012-13, 2013-2014 and 2014-15 to evaluate the four irrigation regimes (gravity-fed drip irrigation schedule at 0.6, 0.8 and 1.0 of pan evaporation replenishment, E0 including surface irrigation as control) and three settings of nitrogen nutrition (100% RDN as vermicompost, 50% RDN as vermicompost + 50% RDN as fertilizer and 100% RDN as fertilizer) on gladiolus cv. American beauty. The results showed that under assured irrigation water supply, maximum spike and corm yields, gross return, net return and BCR (3.44) was obtained with optimal drip irrigation at 1.0 E0 with 50% RDN as vermicompost + 50% RDN as fertilizer. However, under limited irrigation water supply, moderate deficit drip irrigation at 0.8 E0 with 50% RDN as vermicompost + 50% RDN as fertilizer was found most viable alternative in deriving higher yields, gross return, net return and BCR (3.32). Under water scarce, reasonable good yields, gross return, net return and BCR (2.62) was accomplished with higher deficit drip irrigation at 0.6 E0 with 50% RDN as vermicompost + 50% RDN as fertilizer. The findings highlight the techno-economic feasibility of low-cost gravity drip irrigation and nitrogen management for efficient utilization of available groundwater and nitrogen resources for profitable gladiolus cultivation in Gangetic alluvial plains of eastern India.

Effect of regulated deficit irrigation on yield and water use efficiency of grapes

Thompson Seedless grafted on Dogridge was irrigated at variable rates of pan evaporation replenishment at different growth stages for consecutive five years (2012–13 to 2016–17) with the objective of developing the grower friendly irrigation schedule. The new schedule standardized by applying regulated deficit irrigation (RDI) to the vines at the rate of 60% evaporation replenishment (ER) at shoot growth and berry setting to harvest and at the rate of 20% ER at bud differentiation and development, bloom to shatter stage saved considerable amount of water (45.7%) without affecting the yield and quality of the grapes. In the standardized RDI schedule, 460 mm of irrigation water was applied to realize a Brix yield of 4t/ha with a WUE of 0.34 t/cm/ha when compared to standard irrigation control STD 80-T1 (irrigating at uniform rate of 80% ER at all the growth stages) where 848 mm irrigation water was applied to attain a brix yield of 3.5t/ha with a WUE of 0.18 t/cm/ha. The petiole nutrient content at bud differentiation was not significantly influenced by irrigation treatments. However, at full bloom stage significantly low petiole N content was recorded in SDI 40-T3(irrigating at 40% ER at all growth stages) and RDI-T6 irrigating at 40% ER and reducing to 20% ER at bud differentiation, cane maturity, fruit bud development and bloom to shatter stages) while low petiole P content was recorded only in RDI-T6.

Evaluating stage-wise irrigation water requirement of sweet orange (Citrus sinensis) c.v. Sathgudi grown on Alfisols

A field experiment on stage-wise water requirement was conducted on pan evaporation replenishment through drip irrigation system in a 10-year-old bearing sweet orange (Citrus sinensis Osbeck) cv. Sathgudi at AICRP Fruits(Citrus), Citrus Research Station, Dr YSR Horticultural University, Tirupati, Andhra Pradesh, during 20122017. The treatments comprised: irrigation schedule with 30% ER in stage-I, III, V and 40% ER in stages II, IV and VI (T1), irrigation schedule with 40% ER in stage-I, III, V and 60% ER in stages II, IV and VI (T2), irrigation schedule with 60% ER in stage-I, III, V and 80% ER in stages II, IV and VI (T3), irrigation schedule with 80% ER in stage I to VI (T4) and irrigation schedule with 30% ER in stage I to VI (T5) with four replications in a randomized block design. The maximum canopy volume (20m3), average number of fruits of fruits (288 fruits/plant) and total soluble solids (10.63°Brix) were recorded at 80-80-80-80-80-80% ER from stage I (January-February) to stage VI (November-December). However, maximum fruit yield (46.91 kg/plant and 13 t/ha), less incidence of dry root rot (8.33%) and highest benefit: cost ratio (1.48) were recorded at 60-80-60-80-60-80% ER in stages I to VI. The reduction in irrigation from 80% ER to 30% ER during any stage resulted in consequent reduction in yield from 13.00 to 10.19 t/ha. Hence, it is recommended that irrigation at 60-80-60-80-60-80% ER from stages I (January-February) to VI (November-December) for better plant growth, fruit yield and quality with efficient utilization of water, besides water saving of 13% per plant and highest benefit with and also low incidence of dry root rot disease (8.33%) for Ambia bahar crop of sweet orange under Rayalaseem region of Andhra Pradesh.

Yield and economic return response of silage maize to different levels of irrigation water in a sub-humid zone

Field studies were conducted during the summers of 2007 and 2008 to determine the response of silage maize (Zea mays L.) to different levels of irrigation water to guide programs for the development of improved irrigation management practices for sub-humid zones. The experiments were carried out in Bursa, Marmara region, Turkey. Silage maize plants (cv. ‘Ada-523’) were subjected to different levels of irrigation using a drip system in the field on a clay-loam soil. Fully irrigated (FI = 100%) plants were irrigated at 100% pan evaporation (Epan) replenishment with 7-day intervals. In other treatments, irrigation was applied as excessive (EI = 125% Epan) and deficit (DI-75 = 75% Epan, DI-50 = 50% Epan, DI-25 = 25% Epan, NI – no irrigation). Plant height, first ear height, stem diameter, number of ears per plant and net income decreased with decreases in the amount of irrigation, but the effect of soil water deficit on the number of leaves per plant and ear ratio in forage was minor. The highest forage yields were obtained with EI (125% Epan), FI (100% Epan) and DI-75 (75% Epan) treatments. FI treatment produced the highest net income based forage yield. Severe soil water deficit substantially reduced forage yields and net income in both years. The results showed that full irrigation during the whole growing season is preferable for higher forage yield and net income. However, in regions of water scarcity, farmers should adopt the deficit irrigation (DI75 = 75%, DI-50 = 50% and DI-25 = 25% Epan) approach to achieve economically sustainable crop production. As an alternative to full irrigation during the entire growing season, the irrigation at a rate of DI-75% Epan can be recommended as optimal level because it achieved irrigation water savings of 25%, an increase of 16% in forage yield irrigation water use efficiency, satisfactory crop morphological characters and an acceptable net income with a yield loss of only approximately 7% compared with full irrigation.

Effect of drip irrigation and polyethylene mulching on fruit yield and quality of guava cv. Allahabad Safeda under meadow orcharding

A field experiment was conducted during 2009–2012 with an objective of improving yield and quality of guava under drip irrigation and polyethylene mulching in ultra high density planting (2.0 m × 1.0 m). The experiment plot of guava (four-year-old) was irrigated with a drip irrigation system having two emitters per plant of two LPH capacity based on four irrigation levels (40, 60, 80 and 100%) of pan evaporation (PE) replenishment and one ring basin irrigation method (control). UV stabilized black polyethylene mulching (100 μ thickness) was done during October-November (2009). Higher fruit number (27.3), fruit weight (107.3 g) and fruit yield (16.92 kg m−3) were recorded by application of irrigation at 80% PE (T3) per day per plant coupled with black polyethylene mulching. Maximum water saving (47.52%) was recorded through drip irrigation and polyethylene mulching as compared to control (unmulched basin irrigation). Fruit yield varied from a maximum value of 16.92 kg m−3 canopy volume in drip irrigation 80% PE level with black polyethylene mulching as compared to minimum in control (8.21 kg m−3). Drip irrigation coupled with polyethylene mulching resulted in better quality of fruits in terms of increased TSS (12.1°Brix), total sugars (6.61%), ascorbic acid (169.2 mg 100 g−1) and reduced acidity (0.27%) as compared to the minimum TSS (10.1°Brix), total sugars (6.12%), ascorbic acid (159.6 mg/100 g) and increased acidity (0.34%) in control.

Optimizing levels of water and nitrogen applied through drip irrigation for yield, quality, and water productivity of processing tomato (Lycopersicon esculentum Mill.)

The main goal of this study was to evaluate the effects of different levels of irrigation water and nitrogen on yield, quality, and water productivity of processing tomato grown in clay-loam soil. Three water levels of pan evaporation (Epan) replenishment applied via drip irrigation (1.00 × Epan, 0.75 × Epan, and 0.50 × Epan) and four N application rates with fertigation (0, 60, 120, and 180 kg N·ha−1) were tested in the sub-humid climate conditions of Turkey during the 2010 and 2011 growing seasons. The highest marketable yields were observed with full irrigation (1.00 × Epan) for each season. Decreasing irrigation rate generally improved dry matter, total soluble solids, total sugars, titratable acidity, lycopene and total carotene, and decreased fruit NO3-N content and fruit total protein content slightly. The highest water productivity was obtained with a moderate soil water deficit (0.75 × Epan). The 180 kg N·ha−1 fertilization rate produced the highest values for marketable yield, fruit size, total soluble solids yield, NO3-N, and total protein content. Increasing N rate also increased the values of fruit total sugars and titratable acidity. Increasing both irrigation and N levels increased the NO3-N and protein contents. The higher lycopene and total carotene values were obtained in the treatments of 60 and 120 kg N·ha−1. Increasing N supply improved the water productivity with the 3 irrigation application ratios. Considering the quantity and quality for the processing and water productivity, the 0.75 × Epan irrigation regime and a 120 or 180 kg·ha−1 nitrogen supply can considered optimal.

Water requirements in growth stages and effects of deficit irrigation on fruit productivity of drip irrigated Nagpur mandarin (Citrus reticulata)

The field experiment on irrigation scheduling based on pan evaporation replenishment through drip irrigation system was conducted to find out the water requirements in critical growth stages of 8-10 years old bearing Nagpur mandarin (Citrus reticulata Blanco) during 2009-2012 at NRC for Citrus, Nagpur. In this trial five levels of pan evaporation based irrigation schedules with respect to critical water requirement, plant growth, soil and leaf nutrient status, yield and fruit quality was investigated. The irrigations were scheduled on percent of pan evaporation replenishment (ER) in various stages of growth and fruit development. The different stages considered in this study are: Stage-I (Jan-Feb), Stage-II (Mar-Apr), Stage-III (May-Jun), Stage-IV (Jul-Aug), Stage-V (Sep-Oct) and StageIV (Nov-Dec).The treatments were irrigation schedule with 30% ER in stage-I, III, V and 40% ER in stages II, IV and VI (T1), irrigation schedule with 40% ER in stage-I, III, V and 60% ER in stages II, IV and VI (T2), irrigation schedule with 60% ER in stage-I, III, V and 80% ER in stages II, IV and VI (T3), irrigation schedule with 80% ER in stage-I to VI (T4) and irrigation schedule with 30% ER in stage-I to VI (T5) with three replications in Randomized Block Design. The study indicated that the irrigation water requirement of drip irrigated Nagpur mandarin scheduled at 80% ER in stages I to VI ranged from 35.3 to 188.1 litres during 2009-2012. The growth of plant height (4.73 m) and stock girth (66.37 cm) was more in irrigation scheduled at 80% ER in stages I to VI. There is a significant in increase in canopy volume (68.97 m3) in irrigation scheduled at 80% ER in stages I to VI. The average fruit yield recorded was 16.09 tonnes per ha. in irrigation scheduled 80% ER in stages I to VI. The average fruit weight, Total Soluble Solids, juice percentage was high in irrigation at 80% ER in stages I to VI in comparison with other irrigation schedules. The study revealed that the irrigation scheduling at critical water need affect the plant growth, yield and fruit quality of Nagpur mandarin with drip irrigation scheduling less than 80% ER in all stage.

Crop coefficients for prediction of evapotranspiration and irrigation requirements of drip irrigated castor (Ricinus communis L.)

A study was conducted on castor (Ricinus communis L.) in winter 2009-10 at Agricultural College Farm, Rajendranagar, Hyderabad with different drip irrigation schedules at 40, 60 and 80% pan evaporation replenishment levels either kept constant throughout the crop life or combinations at vegetative, flowering and development stages were compared with surface check basin method, irrigated at 0.8 IW/CPE ratio to derive crop coefficients (Kc) for drip irrigated castor. The Kc values were also used to suggest methodology for determination of periodic and peak irrigation requirements of castor for field application. The Kc values worked out varied between 0.345 to 0.822 and the average Kc values for different phenological phases of germination and establishment, vegetative, flowering, capsule development,seed filling and maturity periods were 0.449, 0.626,0.771, 0.940, 0.677 and 0.38, respectively. The peak irrigation, net irrigation and gross irrigation water requirements worked out were 808.7 m , 32.11cm and 3 3567.4 m , respectively for drip irrigated castor.

Research review on Irrigation scheduling and water requirement in citrus

Citrus is the main fruit group grown in tropical as well as sub-tropical climate of more than 150 countries in the world. Irrigation scheduling and water requirement of the citrus crops are one of the main concerns of the modem citrus fruit production irrespective of availability of natural resources. A large number of research findings have emerged world over on irrigation scheduling and water requirements of the citrus based on available soil water content and its depletion and based on pan evaporation replenishment. The research review of the literature has revealed best promising results on irrigation scheduling based on depletion patterns of soil available water content, irrigation schedules of various citrus crops and fertigation. Irrigation water management with proper water use is one of the prime concerns of modem horticulture irrespective of soil and water resource availability. A variety of recommendations have reviewed the world over on irrigation scheduling based on analysis of meteorological parameters, evapo-transpiration, depletion of available water content, soil and leaf water potential. The review of the literature has revealed best promising results on irrigation scheduling based on depletion patterns of soil available water content. Similarly, irrigation scheduling has shown good responses on growth, yield, and quality compared to calender method of irrigation schedules. The present status of the review of irrigation scheduling and water requirement of citrus cultivars is clearly presented in this research review article.

Yield and economic return of drip‐irrigated vegetable production in Turkey

Field experiments were conducted for 2 years (2004 and 2005) on sandy loam soil in south Marmara region of Turkey to study the effect of five levels of pan evaporation replenishment (20%, 40%, 60%, 80%, and 100%) on marketable yield, irrigation water productivity (IWP), and economic return of tomato (Lycopersicon esculentum), pepper (Capsicum annuum), green bean (Phaseolus vulgaris), and eggplant (Solanum melongena) under a drip irrigation method. The highest mean marketable yield (2 years) of tomato (87.5 t ha−1), pepper (59.2 t ha−1), green bean (7.6 t ha−1), and eggplant (46.5 t ha−1) was recorded at 100%, 100%, 80%, 100%, and 80% of pan evaporation replenishment, respectively. The IWP of tomato (23.6 kg m−3), pepper (16.5 kg m−3), green bean (2.6 kg m−3), and eggplant (13.6 kg m−3) was the maximum at 80%, 80%, 40%, and 80% of pan evaporation replenishment, respectively. The results revealed that a further increase in irrigation amount resulting from 100% of pan evaporation replenishment did not increase the marketable yield of crops but reduced the IWP significantly. The net return increased with the increase in pan evaporation replenishment. The results revealed that the pepper is the most profitable crop, followed by tomato, eggplant, and green bean.

Yield, irrigation production efficiency and economic returns of broccoli under variable drip irrigation and lateral spacing.

Field studies were carried out for 2 years (2001 – 2003) on clay loam soil to determine the effect of variable irrigation (50, 100, 150 and 200% of pan evaporation replenishment) and lateral spacing (0.5 and 1.0m) on yield, irrigation production efficiency and economic return of broccoli (Brassica oleracea). The irrigation was applied when sum of daily pan evaporation (5 years) from United States Weather Bureau (USWB) Class A open pan reached approximately up to 16.3mm after accounting for rainfall. The crop was irrigated by drip irrigation system. Irrigation at 150% of pan evaporation replenishment and 0.5m lateral spacing resulted in higher marketable yield of primary and secondary flowers. A further increase in irrigation amount resulted from 200% pan evaporation replenishment reduced marketable flower yield significantly. The higher irrigation production efficiency was recorded at 50% of pan evaporation replenishment and 0.5m lateral spacing and it decreased significantly with an increase in irrigation amount and lateral spacing Irrigation at 150% of pan evaporation replenishment resulted in a higher net return and benefit-cost ratio. The lateral spacing of 1.0m gave higher net return and benefit-cost ratio as compared to lateral spacing of 0.5m. The seasonal water applied and marketable flower yield, gross return, net return and benefit-cost ratio exhibited quadratic relationship which can be used for optimising economic return of broccoli under variable irrigation and lateral spacing. The results revealed that drip irrigation system is profitable for broccoli production inspite of high initial investment.Journal of Science and Technology (Ghana) Vol. 27 (2) 2007: pp. 109-119

Effect of differential soil moisture and nutrient regimes on postharvest attributes of onion (Allium cepa L.)

Abstract Studies were conducted to observe the effect of different soil moisture and nutrient regimes on postharvest attributes of onion irrigated with microsprinkler irrigation system under semi-arid climate for 3 consecutive years (2002–2004). Soil moisture regime consisted of four irrigation treatments based on pan evaporation replenishment (0.60, 0.80, 1.00 and 1.20 Ep). Similarly, three fertigation treatments were tried with nutrient application rates of 100 (50:25:25), 150 (75, 37.5, 37.5) and 200 (100:50:50) kg/ha of NPK. Irrigation and fertigation had marked effect on yield, postharvest attributes and storability of onion. Irrigation at 1.20 Ep and fertigation at 200 kg/ha produced higher bulb and dry matter yield, mean bulb size and weight, which decreased with the decrease in amount of irrigation and fertigation. The percentage of B-grade bulbs, which is considered commercially important, had been considerably higher at 1.20 Ep of irrigation and 200 kg/ha of fertigation. TSS increased up to 1.00 Ep and then declined slightly, whereas it varied with fertigation significantly. A decreasing trend for protein content was recorded with the increase in irrigation from 0.60 to 1.20 Ep, however, protein content increased with increase in fertigation. Irrigation at 0.80 Ep and fertigation @ 200 kg/ha resulted into minimum physiological loss in weight (%) for onion during 60 days of storage. But for extended storage period, increasing fertigation and decreasing irrigation had adverse effect on storability of bulbs. Theoretically, 416 mm irrigation water was found optimum for maximizing the dry matter yield of onion. Studies indicated that onion crop should be irrigated at 1.0 Ep under microsprinkler irrigation regime for better postharvest attributes. Similarly, fertigation @ 150 kg/ha is most desirable for micro sprinkler irrigated onion crop under semi-arid climate of India.

Effect of irrigation level on yield and bioactive amine content of American lettuce

AbstractThe influence of four levels (25, 50, 75 and 100%) of Class A pan evaporation replenishment (PER) on the marketable yield and bioactive amine content of American lettuce (Lactuca sativa cv Lucy Brown) grown under greenhouse conditions and drip irrigation was investigated. Lettuce was planted in 1.20 m × 2.10 m plots in a completely randomised block design with three replications. Lowest fresh head weights and diameters were obtained at 25% PER. Highest marketable yields and fresh head weights were obtained at 100% PER; however, no significant difference was observed when using 75% PER. The fresh head diameter was smaller only when using 25% PER. Four amines were detected in lettuce grown under 100% PER, with a total content of 7.60 mg kg−1. Spermidine was the prevalent amine, followed by putrescine, cadaverine and agmatine. Higher spermidine and cadaverine levels were observed in the outer layers of leaves than in the intermediate and inner leaves. The contents of every amine except agmatine increased with water stress; however, a significant difference was observed only between 100 and 25% PER. The concentrations of accumulated putrescine were not capable of negatively affecting the sensory quality of the lettuce. Copyright © 2005 Society of Chemical Industry

Yield and economic return of vegetable crops under variable irrigation

Field experiments were conducted for 2 years (1997 and 1998) on sandy loam soil in northwestern Botswana to study the effect of five levels of pan evaporation replenishment (20, 40, 60, 80 and 100%) on marketable yield, yield components, irrigation production efficiency and economic return of winter broccoli, carrot, rape and cabbage under a drip irrigation method. The highest mean marketable yield (2 years) of broccoli (19.1 t/ha), carrot (58.9 and 32.9 t/ha), rape (61.8 t/ha) and cabbage (97.2 t/ha) was recorded at 80% of pan evaporation replenishment. The irrigation production efficiency of broccoli (5.9 kg/m3), rape (14.6 kg/m3) and cabbage (23.6 kg/m3) was maximum at 80, 20 and 60% of pan evaporation replenishment respectively. Irrigation replenishment up to 80% of pan evaporation loss did not influence the irrigation production efficiency for total and root yield of carrot. The results revealed that a further increase in irrigation amount resulting from 100% of pan evaporation replenishment did not increase the marketable yield of crops but reduced the irrigation production efficiency significantly. The seasonal water applied and marketable yield of broccoli, carrot, rape and cabbage showed quadratic relationships (R2 = 0.85–0.98), which can be used for allocating irrigation water within and between the crops. The net return increased with the increase in pan evaporation replenishment. The results revealed that the rape crop is the most remunerative, followed by cabbage, broccoli and carrot.