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In order to assess the climatological risk in terms of the dry week probabilities and length of the growing period of Indian Sundarbans region for successful crop planning, the present study was conducted using long term rainfall data from 1984 to 2018 received in Gosaba CD (Community Development) block of Indian Sundarbans. The probability of a rainfall events with 25 %, 50%, 75 % probabilities were estimated. Markov Chain model was used to estimate the initial, conditional probabilities of dry and wet weeks along with the probability of two consecutive wet and dry weeks considering 10 mm and 20 mm rainfall thresholds. Length of growing period (LGP) was calculated using Moisture adequacy index computed by the soil water balance method of Thornthwaite and Mather. Weekly rainfall varied from 1.11 mm in 51st Standard Meteorological Week (SMW) with standard deviation of ± 3.41 to 88.49 mm in 29th SMW with standard deviation of ± 58.19.50 % chance of getting more than 20 mm and 10 mm weekly rainfall was observed from 20th (23.37 mm) to 41st SMW (30.64 mm) and 17th (14.63 mm) to 42nd SMW (16.87 mm) respectively. The risk of dry spells was very higher from 42nd to 17th SMW. Average LGP of the study area was 237.4 days with standard deviation of ± 29.88.Probability of a week being stress free growing period and moderately drought period was more than 50 % from 18th to 48th SMW and 49th to 5th SMW respectively. Grass pea, potato with straw mulch and green gram can be included in the rice based cropping system during winter and summer seasons for sustainable intensification of the cropping systems in Indian Sundarbans region.

The present study was conducted to analyze cropping intensity of four blocks (Mogra-Chinsurah, Polba-Dadpur, Singur and Haripal) of the Gangetic alluvial zone of India using multi-dated Sentinel-2 data in 2018–19 cropping year. It was observed that during peak growing stage all crops ascribed higher Normalized Difference Vegetation Index NDVI values (0.4 to 0.73) and NDVI became as low as 0.06 when the fields were vacant. Sentinel-2 data acquired in the peak crop growing period during each cropping season were carefully selected, and NDVI was computed over the whole study area. Rule-based classification was applied for cropping sequence and cropping intensity classification based on the occurrence and non-occurrence of crops using NDVI threshold (0.4). Sentinel-2 images acquired on 22/10/2018, 6/12/2018, 30/1/2019 and 30/4/2019 were used for masking of trees and non-agricultural area. October 22, January 30 and April 30 imageries demonstrated peak crop growing period during kharif, rabi and pre-kharif seasons whereas December 6 image represented occurrence of no or little crop in the study area. Crop acreage was the highest in Polba-Dadpur block during all the three seasons. The crop–fallow—crop sequence occupied the highest areas (43%) followed by crop–crop–crop sequence (39%). 50% and 39% of the total cultivated land was under 200% and 300% cropping intensities. Overall, accuracies of cropping system and cropping intensity classification were 88.54% and 87.85%, respectively. Sentinel-2 data can be successfully used for cropping system analysis which helps in crop planning and management.

Most simulations of food production in response to various climates to date have used simulations of the same crop over multiple years. This study evaluated the impact of projected climate on performance of rice-lentil-groundnut cropping sequence in New Alluvial Zone of West Bengal, India, using DSSAT model. The study period consisted of baseline (1980–2010), mid-century (2040–2069) and end-century (2070–2099). Advancement in days to anthesis (2–13 days) was simulated for rice during the future periods. For lentil and groundnut, average advancement in days to anthesis was 1 day. Days to maturity were shortened by 3–16 days for rice and 0–7 days for lentil. Nevertheless, for groundnut, the days to maturity were simulated to increase by 1–9 days. The impact on final biomass and yield was simulated with and without CO2 fertilization, and the positive impact of CO2 fertilization was prominent for all the three crops. When CO2 fertilization effect was considered, the yield of rice was projected to increase by 11–32%. On the other hand, yield of lentil and groundnut was estimated to change by − 31 to − 12% and − 33 to + 8%, respectively. Enhanced CO2 could mitigate the magnitude of yield reduction due to enhanced temperature. Rice was benefited due to the carryover effect of residue from preceding groundnut and, hence, could sustain the yield on a long term. The study could also quantify the uncertainty in simulation of yield due to selection of GCMs.

Cropping intensification is a solution to ensure global food security amid the threats of climate change and variability. Crop models are used extensively to evaluate the performance of single crop for a particular year under future climate. However, very few literatures are available on the application of crop models to evaluate intensive cropping systems. The study attempts to address this issue by evaluating the impact of projected climate derived from 29 GCMs during four future scenarios (mid and end-century under RCP4.5 and RCP8.5) on the performance of rice–wheat-groundnut cropping sequence in Mohanpur, India, using the sequence analysis module of DSSAT. A marked reduction in crop duration was simulated for rice (4 to 17 days) and wheat (1 to 16 days) during all four future scenarios. On the contrary, the duration of groundnut increased by 1–4 days. Under elevated CO2 concentration, an increase in biomass was simulated for all three crops. During future periods under elevated CO2, the yield of rice tends to increase under all the future scenarios whereas wheat and groundnut could decrease the magnitude of yield reduction due to an increase in temperature. Rice was benefited due to the carry-over effect of residue from preceding groundnut and, hence, could sustain the yield on the long-term. The uncertainty in simulation due to the selection of GCMs was also quantified. The study provided a better understanding on how a cropping sequence responds to projected climate rather than a single crop in a sequence, which can be used to develop better adaptation strategies.

A traditional scented rice (cv. Radhunipagal) was tested under varied spacing (20 cm × 20 cm, 20 cm × 15 cm, 15 cm × 15 cm and 20 cm × 10 cm) and seedling age (25, 35 and 45 days) during wet (kharif) season of 2018 at B.C.K.V., Nadia, West Bengal. Seedling age caused significant variation in life duration and summed GDD from 147.9 days and 2436°C day (25-day aged) to 162.0 days and 2753°C day (45-day aged), but with maturity in same meteorological week. Square planting (15 cm × 15 cm or 44 hills m-2) resulted in highest grain yield (2.52 t ha-1), which was 2.85, 11.01 and 4.56% greater over wider (20 cm × 15 cm and 20 cm × 20 cm) and closer spacings (20 cm × 10 cm). Radhunipagal rice raised with 25-days old seedlings recorded the highest grain yield (2.53 t ha-1) and maximum heat use efficiency (0.90 kg ha-1 °C day-1), and that yield was 0.12 and 0.22 t ha-1 greater over the crops planted with 35 and 45-days old seedlings during wet season. Spacing could not influence the cooking and processing quality (gelatinization temperature, kernel elongation ratio and aroma) except protein content of milled rice in the study. Radhunipagal paddy planted with 45-day aged seedlings recorded maximum protein content (6.36%) and alkali spreading value (score 3.27).

The research portrays the fate of a new herbicide mixture of fomesafen and quizalofop-ethyl. The soil samples viz. red lateritic soil (A), coastal saline soil (B) and black soil (C) were fortified separately for fomesafen and quizalofop-ethyl at 0.5 (T1) and 1.0 mg kg−1 (T2) doses and incubated at 20, 30 and 40°C. A satisfactory mean recovery, precision and linearity proved that the methods were accurate. Both the herbicides followed first + first order kinetics. Higher persistence of fomesafen was observed in Soil C than Soil B and Soil A with 22.38–53.75 days half-life, whereas quizalofop-ethyl showed higher stability in Soil A than Soils B and C with half-life of 0.93–12.07 days. Both compounds showed faster rates of dissipation at increased temperature, irrespective of soil type. The current study will help to predict the effect of temperature on the dissipation of herbicides in different soil under real field scenario.

The costal saline zone of West Bengal in India is the home for millions of the world’s poorest and most vulnerable people. Due to gradual increase in salt accumulation on soils of the costal saline zone of West Bengal in India from winter to summer days, cultivation of the second crop in winter season becomes possible in a limited area. To address this issue, field experiment was conducted both in rainy and winter seasons of 2016–2017 and 2017–2018 in this zone to study the feasibility of incorporating different winter pulses (lentil and grass pea) in the rice based cropping system. The experiment was conducted in strip plot design having two factors namely, Factor I: Six dates of sowing of rice at an interval of one week (2nd week of June to 3rd week of July) and Factor II: Two land situations (Medium-upland and Medium-lowland). Date of sowing significantly influenced dry matter and macro-nutrients (NPK) partitioning in rice. Irrespective of land situation, crop sown on 1st and 2nd dates recorded significantly higher grain yield and macro-nutrient uptake by rice. Date of sowing of rice and land situation also significantly influenced the seed and stover yield of different pulse crops. Pulse crops sown on 1st and 2nd dates recorded significantly higher seed yield in coastal saline ecology of West Bengal, India.

This study compares thirteen rice-based cropping systems in the coastal part of West Bengal, India in terms of productivity, profitability, energetics, and emissions. Information on the crop management practices of these systems was collected on 60 farms through a questionnaire survey. Rice-bitter gourd system was observed to have the highest system yield (49.88 ± 4.34 tha-1yr-1) followed by rice-potato-ridge gourd (37.78 ± 2.77 tha-1yr-1) and rice-potato-pumpkin (36.84 ± 2.04 tha-1yr-1) systems. The rice-bitter gourd system also recorded the highest benefit:cost ratio (3.92 ± 0.061). The lowest system yield and economics were recorded in the rice-fallow-fallow system. Rice-sunflower system recorded highest specific energy (2.54 ± 0.102 MJkg-1), followed by rice-rice (2.14 ± 0.174 MJkg-1) and rice-fallow-fallow (1.91 ± 0.327 MJkg-1) systems, lowest being observed in the rice-bitter gourd (0.52 ± 0.290 MJkg-1) and rice-pointed gourd (0.52 ± 0.373 MJkg-1) systems. Yield-scaled GHGs (YSGHG) emission was highest (1.265 ± 0.29 t CO2eqt-1 system yield) for rice-fallow-fallow system and was lowest for rice-vegetable systems. To estimate the uncertainty of the YSGHG across different systems under study, Monte-Carlo Simulation was performed. It was observed that there was a 5% probability of recording YSGHG emission > 1.15 t CO2eqt-1 system yield from different cropping systems in the present experiment. Multiple system properties such as productivity, economics, energy, and emission from all rice-based systems taken together, the rice-vegetable system performed consistently well across parameters and may be practised for higher economic returns with judicious and sustainable utilization of resources in the coastal saline tracts of the region.

Tuber initiation and tuber bulking stages are critical part of various phenological phases for potato production. Tuber initiation covers the period from the formation of spherical rhizome ends, the flowering and the start of tuber bulking. In general, the tuberization spans from 3 to 5 weeks after emergence and ends with the row closer i.e. canopies in adjacent rows touch each other across the furrow. Hence, this rapid growth seeks critical agronomic management practices such as irrigation and fertilization. It majorly influences the growth of stems, foliar area, dry weight and number of tubers particularly at the phase of tuber initiation. During these phenological stages, potato crops are susceptible to the infestation of late blight diseases caused by Phytophthora infestans and largely affects the potato production. Thus identifying the crop risk using remote sensing approaches can provide an efficient potato growth monitoring framework. In the context of monitoring crop dynamics, quad-pol Synthetic Aperture Radar (SAR) data has proven to be effective due to its sensitivity towards dielectric and geometric properties. In addition to SAR data, optical remote sensing data derived vegetation information can provide an improved insight into crop growth when combined with SAR data. In this research, quad-pol RADARSAT-2 and Sentinel-2 optical data are analyzed to monitor potato tuberization phase over Bardhaman district in the state ofWest Bengal, which is one of the major potato growing regions in India. The proposed approach uses polarimetric parameters such as backscatter intensities, ratio (HH/VV, VH/VV, linear depolarization ratio), and co-pol correlation (ρHH–VV) along with the vegetation indices derived from the Sentinel-2 data for understanding the spatio-temporal dynamics. The initial results show a promising accuracy in monitoring the dynamics of potato tuberization. Integration of such earth observation (EO) data, in conjunction with in-situ field measurements, might significantly enhance the current capabilities for crop monitoring.

The Costal Saline Zone (CSZ) of West Bengal, India is dominated by rice-fallow-fallow system cropping system. Only 4% of the cultivated area of the coastal zone can be irrigated with available sweet water. To cope up with the present situation is introduction of new high value crops to catch the fallow winter period emphasizing on water saving technologies. In this way mono-cropped saline soils of coastal region can be converted into multiple cropping through the adoption of zero tillage potato technology. Soils of the CSZ show multi-nutritional deficiencies and these deficiencies adversely affect the crop. To address this issue, field experiment was conducted in winter season of 2016−2018 in CSZ of West Bengal, India with the focal objectives of studying the feasibility of potato under zero-tilled-mulched condition in CSZ of West Bengal; assessing the effect of foliar nutrient management practices on growth, yield, quality and economics of potato. The foliar nutritional supplementation with 2% Urea at 30 & 50 days after planting (DAP) of potato along with 0.1% Boron at 30 DAP not only increased tuber number and yield but also quality parameters of potato tuber such as TSS, tuber hardness, vitamin C etc. were significantly increased. It may thus be concluded that 2% Urea at 30 & 50 at DAP of potato along with 0.1% Boron at 30 DAP as foliar application is the best foliar nutrient management option for potato grown under zero tillage and mulching in coastal saline soils of West Bengal, India.

Field spectroscopic study was performed using a hand-held Field Spectroradiometer to examine spectral variability between healthy and late blight disease infected potato canopy. The purpose was to select a suitable spectral feature in the visible-near infrared region for late blight disease initiation and severity during winter season. The spectral regions at which significant differences in bio-optical response was observed between healthy and diseased canopy include, 680-730nm (47.84%), 750-900nm (76.14%) and 860-1040nm (68.60%). Correlation study was carried out among different spectral variables, sensitive to PLB disease, and field measured PLB disease severity. Out of all the spectral variables, Red-Edge Normalised Difference Vegetation Index (NDVI705) and Disease Water Stress Index (DWSI) showed significant negative correlation (0.87 and 0.84 at 95% confidence level) and capable to predict the different level of potato late blight disease severity. A remote sensing based novel disease severity method was developed from the above mentioned spectral variables using multi-linear regression model and validated with very high correlation (R2 = 0.883). The scoring method developed could be a good proximal indicator for real-time field monitoring of potato late blight disease.

Due to seasonal dry-season salt accumulation in the coastal saline zone (CSZ) of West Bengal, India, the cultivation of winter crops (following summer rice) is rare. To address this issue, field experiments were conducted over two years (2016–18) in the CSZ to study the feasibility of cropping system intensification through incorporating grass pea into the dominant rice-fallow rotation. The experiment was conducted in strip plot design with two factors namely, Factor A: Six dates of rice sowing (at one-week intervals—2nd week of June to 3rd week of July) and Factor B: Two land situations (Medium-upland and Medium-lowland). The experiment was simulated using APSIM (Agricultural Production Systems sIMulator) utilizing the APSIM-SWIM water balance module to understand the mechanisms of seasonal soil salinity dynamics and the associated crop responses. The results suggest that irrespective of land situation, early sown rice (2nd week of June) produces higher dry matter and yield compared to late sown crops. This early rice sowing also facilitated better subsequent grass pea performance, by avoiding the worst of the salinity build-up and drought stress later in the winter. The model performed well in simulating the observed rice and grass pea yields (R2 = 0.97 with low bias (slope, α = 0.93, intercept, β = 149 kg ha−1), RMSE = 558 kg ha−1). It may be concluded that ASPIM-SWIM is an effective tool to understand, assess and predict the complex bio-physical mechanisms of ground water and soil salinity dynamics in rice-pulse-based cropping systems of CSZ of West Bengal.

A new metric called “Delta Area at Near Infrared Region” ( ${\text{DA}}_{{\text{NIR}}}$ ) has been conceptualized and implemented for estimation of green vegetation fraction (GVF) using field spectroradiometer at different growth stages of potato over two consecutive potato growing seasons (2012–2013 and 2013–2014). Vertical photograph, collocated in time and space with spectroradiometer observation, was acquired and digitally classified for GVF. While comparing with other conventional indices, ${\text{DA}}_{{\text{NIR}}}$ showed linearity at higher GVF values and capable of capturing the movement of the curve caused by soil-vegetation mixture between inflection point and near infrared peak. Among all the univariate models, ${\text{DA}}_{{\text{NIR}}}$ showed the highest accuracy with ${\text{R}}^{2}=0.94$ and ${\text{RMSE}}=7.0$ . The new index also exhibited the highest sensitivity for the entire range of GVF while comparing with other indices; however, the sensitivity decreases at higher values especially above 70%. Stepwise multiple linear regression (SMLR) and partial least squares regression (PLSR) were performed using all the spectral variables. The prediction accuracy was further improved over univariate analysis wherein PLSR was able to predict the vegetation fraction with the highest accuracy ( ${\text{R}}^{2}=0.94$ and ${\text{RMSE}}=5.32$ ). In both SMLR and PLSR, ${\text{DA}}_{{\text{NIR}}}$ contributed significantly to improve the estimation accuracy. These findings suggest that ${\text{DA}}_{{\text{NIR}}}$ can be used as a surrogate indicator of GVF independently or in combination with other vegetation indices to further improve the estimation accuracy.

The accumulative moisture stress of potato crop was detected using Field Spectroradiometer data. Different degree of stress was created by manipulating the amount and interval between two consecutive irrigations. The daily soil moisture was simulated using Hydrus-1D and validated (r = 0.805 and RMSE = 0.015). The ambient soil moisture 0.9), at higher level of accumulative stress beyond 5.0, the values get saturated except for 1091–1303 nm. Hence, the band-depth-maxima at 1091–1303 nm is sensitive to wider range of stress and may be used for targeted irrigation technique to maintain safe irrigation zone.

In the coastal zone of the Ganges Delta, water shortages due to soil salinity limit the yield of dry season crops. To alleviate water shortage as a consequence of salinity stress in the coastal saline ecosystem, the effect of different water-saving (WS) and water-conserving options was assessed on growth, yield and water use of tomato, two field experiments were carried out at Gosaba, West Bengal, India in consecutive seasons during the winter of 2016&ndash, 17 and 2017&ndash, 18. The experiment was laid out in a randomized block design with five treatments viz., surface irrigation, surface irrigation + straw mulching, drip irrigation at 100% reference evapotranspiration (ET0), drip irrigation at 80% ET0, drip irrigation at 80% ET0 + straw mulching. Application of drip irrigation at 80% ET0 + straw mulching brought about significantly the highest fruit as well as the marketable yield of tomato (Solanum lycopersicum L.). The soil reaction (pH), post-harvest organic carbon, nitrogen, phosphorus and potassium (N, P and K) status and soil microbial population along with the biochemical quality parameters of tomato (juice pH, ascorbic acid, total soluble solids and sugar content of fruits) were significantly influenced by combined application of drip irrigation and straw mulching. Surface irrigation significantly increased the salinity level in surface and sub-surface soil layers while the least salinity development was observed in surface mulched plots receiving irrigation water through drip irrigation. The highest water productivity was also improved from drip irrigation at 80% ET0 + straw mulched plots irrespective of the year of experimentation. Such intervention also helped in reducing salinity stress for the tomato crop. Thus, straw mulching along with drip irrigation at 80% ET0 can be recommended as the most suitable irrigation option for tomato crop in the study area as well as coastal saline regions of South Asia. Finally, it can be concluded that the judicious application of irrigation water not only increased growth, yield and quality tomatoes but also minimized the negative impact of soil salinity on tomatoes grown in the coastal saline ecosystem of Ganges Delta.

Water stress in plant is associated with reduced availability of soil moisture under higher ambient temperature and wider vapour pressure deficit for a considerable period of time. Instruments like pressure chambers and porometers are being used to quantify crop water stress under field conditions, but their use is limited because of the numerous time-consuming measurements that must be made. The application of thermal indices involving canopy temperature for monitoring crop water stress and irrigation scheduling has been demonstrated by several researchers in the last five decades since the evolution of portable infrared thermometers in the 1960s. As the temperature of plant canopy is a manifestation of canopy energy balance, a water-stressed canopy is hotter than a well-watered one under the same environmental conditions. Infrared thermometer integrates the thermal radiation from all exposed surfaces in the field of view of the instrument that included the plant surface and exposed soil surfaces into a single measurement and converts it into temperature unit applying the principle of Stefan-Boltzmann law. However, different plant physiological as well as microclimatic factors like solar radiation, turbulence, air temperature and humidity must influence the canopy temperature at the time of observation. Hence, stomatal conductance and transpiration rates cannot be estimated by canopy temperature alone. In other words, canopy temperature alone is not enough to make estimates of plant water status. For this reason many researchers have attempted to normalize the canopy temperature to account for the influence of other variable microclimatic parameters like vapour pressure deficit, air temperature, wind speed, solar radiation, etc.

The regional impacts of future climate changes are principally driven by changes in energy fluxes. In this study, measurements on micrometeorological and biophysical variables along with surface energy exchange were made over a coniferous subtropical chir pine (Pinus roxburghii) plantation ecosystem at Forest Research Institute, Doon valley, India. The energy balance components were analyzed for two years to understand the variability of surface energy fluxes, their drivers, and closure pattern. The period covered two growth cycles of pine in the years 2010 and 2011 without and with understory growth. Net short wave and long wave radiative fluxes substantially varied with cloud dynamics, season, rainfall induced surface wetness, and green growth. The study clearly brought out the intimate link of albedo dynamics in chir pine system with dynamics of leaf area index (LAI), soil moisture, and changes in understory background. Rainfall was found to have tight linear coupling with latent heat fluxes. Latent heat flux during monsoon period was found to be higher in higher rainfall year (2010) than in lower rainfall year (2011). Higher or lower pre-monsoon sensible heat fluxes were succeeded by noticeably higher or lower monsoon rainfall respectively. Proportion of latent heat flux to net radiation typically followed the growth curve of green vegetation fraction, but with time lag. The analysis of energy balance closure (EBC) showed that the residual energy varied largely within ±30% of net available energy and the non-closure periods were marked by higher rainspells or forced clearance of understory growths.

An experiment was conducted to study regrowth and yield of coriander influenced by nitrogen (N) with five different urea doses (0, 1.5, 2.0, 2.5, 3.0% by volume) as foliar spray. Spraying of urea has a significant impact on growth and yield in the second cut. Leaf emergence rate (LER) was higher during initial growth phase and then drastically reduced until first cutting, whereas the stem elongation rate (SER) recorded its peak value during 75-105 DAS. Impact of foliar spray was conspicuous during the later phase of regrowth with the treatment of 2.5% urea achieving the highest SER. Additional return due to spraying was positive up to a dose of 2.5% urea and decreased thereafter. Hence, the study indicated that a foliar spray of nitrogen (2.5% urea) may be beneficial for coriander leaf production under multicut system and the crop is sensitive to rainfall, phototemperature, and morning humidity.

Winter pigeon pea can be considered as an alternative to boro rice cultivation particularly in the places where over exploitation of ground water is a potential threat to sustainability. The present experiment was aimed at quantifying the meteorological factors that limit the cultivation of rabi pigeon pea particularly in the upland and medium land condition. The experiment was conducted for three consecutive years during 2003-06 in the University Farm at (BCKV) Kalyani W.B. The treatments comprised different dates of sowing at seven days interval between 20 September and 7 December. The influence of meteorological factors on phenological development and yield was statistically analysed. The results revealed that the length of vegetative phase was inversely correlated to the afternoon vapour pressure deficit, average BSH and diurnal variation in temperature. On the other hand, night temperature and daylength were negatively correlated with the reproductive duration. The regression analysis showed that bright sunny days with high atmospheric vapour demanded not only induced early flowering but they also had suppressed the grain yield. Higher accumulation of GDD and PTU during vegetative phase resulted in higher grain production. On the other hand, the average day temperature, night temperature and day length during reproductive phase had negative correlation with grain yield of pigeon pea. These parameters may be considered as limiting factors for higher production. Besides that, rainfall during March had severely hampered pod formation when sown late.

Frequency and depth of irrigation play crucial role in crop yield and use efficiency of water resource. To test this hypothesis a field study was carried out in November to January of 2001�2002 to 2003�2004 on a sandy loam (Aeric haplaquept) for quantifying the frequency and depth of irrigation on growth, curd yield (CY) and water use pattern of cauliflower (Brassica oleracea L. var. botrytis). Four irrigation frequencies depending on the attainment of cumulative pan evaporation (CPE) values of: 25 (CPE25), 31(CPE31), 38 (CPE38) and 45 (CPE45) mm were placed in main-plots, with three depth of irrigation (IW) of 35 (IW35), 30 (IW30) and 25 (IW25) mm in sub-plots. Water use efficiency (WUE), net evapotranspiration efficiency (WUEET) and irrigation water use efficiency (WUEI) were computed. Marginal water use efficiency (MWUE) and elasticity of water productivity (EWP) were calculated using the relationship between CY and seasonal actual evapotranspiration (SET). A continuous increasing trend in growth parameters, yield and WUEI was recorded with the increase in SET from CPE45�IW25 to CPE31�IW30. However with further increase in SET the same decreased up to CPE25�IW35 regime. Highest WUE and WUEET obtained under CPE38�IW35 regime where SET value was 5% lower than the status of SET under CPE31�IW30. This study confirmed that critical levels of SET needed to obtain maximum curd yield or WUE, could be obtained more precisely from the knowledge of MWUE and EWP.

The amount of water used by any crop largely depends on the extent to which the soil water depletion from the root zone is being recharged by appropriate depth of irrigation. To test this hypothesis a field study was carried out in November–March of 2002–2003 and 2003–2004 on a sandy loam (Aeric haplaquept) to quantify the effect of depth of irrigation applied through micro-sprinklers on onion (Allium cepa L.) bulb yield (BY) and water use patterns. Seven irrigation treatments consisted of six amounts of sprinkler applied water relative to compensate crop (Kc) and pan (Kp) coefficient-based predicted evapotranspiration loss from crop field (ETp) (i) 160% of ETp (1.6ETp); (ii) 1.4ETp; (iii) 1.2ETp; (iv) 1.0ETp; (v) 0.8ETp; (vi) 0.6ETp; (vii) 40 mm of surface applied water whenever cumulative pan evaporation equals to 33 mm. Water use efficiency (WUE), net evapotranspiration efficiency (WUEET) and irrigation water use efficiency (WUEI) were computed. Marginal water use efficiency (MWUE) and elasticity of water productivity (EWP) of onion were calculated using the relationship between BY and measured actual evapotranspiration (ETc). Yield increased with increasing sprinkler-applied water from 0.6 to 1.4ETp. Relative to the yield obtained at 0.6ETp, yield at 1.0ETp increased by 23–25% while at 1.4ETp it was only 3–9% greater than that at 1.0ETp. In contrast, yield at 1.6ETp was 9–12% less than that at 1.4ETp. Maximum WUE (7.21 kg m−3) and WUEET (13.87 kg m−3) were obtained under 1.0ETp. However, the highest WUEI (3.83 kg m−3) was obtained with 1.2ETp. The ETc associated with the highest WUE was 20% less than that required to obtain the highest yields. This study confirmed that critical levels of ETc needed to obtain maximum BYs, or WUE, could be obtained more precisely from the knowledge of MWUE and EWP.