Crop water productivity and economic evaluation of drip-irrigated soybeans (Glyxine max L. Merr.)
© Adeboye et al. 2015
Received: 28 November 2014
Accepted: 28 July 2015
Published: 19 August 2015
Effective management of water under irrigated agriculture is crucial to ensure food security. One crop that has high irrigation economic potential at local and international scales is soybean. This article presents the outcome of field experiments conducted in the dry seasons of 2013 and 2014 in Nigeria on the effects of deficit irrigation (DI) practices on reproductive stages of soybean. The experimental factor was the timing of irrigation. The five treatments were full irrigation (FI); skipping of irrigation every other week during flowering; pod initiation; seed filling and maturity stages.The crop was planted in a randomized complete block design with three replicates and inline drip irrigation was used to apply water. Leaf area index, dry above-ground biomass and seed yield were measured and the soil water balance approach was used to determine seasonal crop water use.
Seasonal crop water use for the treatment in which deficit irrigation was imposed at seed filling stage was 364 mm while for the control treatment with full irrigation, seasonal crop water use was 532 mm. The seed yield reduced by 18.8 and 21.9% when DI was imposed during flowering and pod initiation, respectively. Similarly, the seed yield reduced by 24.4 and 47.9% when DI was imposed during maturity and seed filling. Water productivity (WP) reduced by 6.8 and 12.4% when DI was used during flowering and pod initiation, respectively. However, WP reduced by 20 and 35% during maturity and seed filling. DI during reproductive stages reduced economic water productivity by 6.7–35% while revenue was reduced by 18.5–47.7%.
Full irrigation should be practiced to maximize water productivity. Weekly skipping of irrigation during seed filling will substantially reduce the seed yield and water productivity while skipping during flowering may be a viable option when water is scarce and land is not limiting. Economic evaluation will guide policy makers at basin scales for formulating improved and efficient water management plans under all varying weather conditions. DI can be used to optimise water productivity. The results will be beneficial in adopting deficit irrigation in a manner that will improve economic water productivity.
KeywordsSoybean Deficit irrigation Dry above-ground biomass Water productivity Irrigation water productivity Harvest index Nigeria
The need for reduction in water use by agriculture is being advocated globally due to stiffer competition among fresh water users such as industry and the environment. Several suggestions have been made to optimize the use of water for crop production. One of them is that water should be applied to crops when they need it most, that is when shortage of water could lead to significant reduction in yield. This approach is called regulated, pre-planned or deficit irrigation (DI) . DI is a means of reducing crop water use while minimizing adverse effects on crop yield [2–4]. In order to adopt DI, information on the responses of crops to water deficit at various stages is required.
Articles have been published on the possibility of saving irrigation water without significant reduction in the yield through DI. Available data show that an equivalent or greater yield can be obtained by delaying irrigation until soybeans are in the reproductive stage of growth as compared with (FI) full irrigation . Stegman et al.  stated that a short period of water stress during flowering may lead to a drop in flowers and pods at the lower canopy but this will be compensated by increased pod set at the upper node when irrigation resumes later in the crop life. Stegman et al.  concluded that water stress in the full pod to seed fill stage was most detrimental to yield in soybeans. A parameter for assessing the effect of DI on crop yield is called the crop response factor (ky). It is the measure of sensitivity of a crop to DI . Crop response factors vary from one crop to the other, cultivar, stage of growth, duration of DI, irrigation method and management. A value of ky greater than 1 indicates that the expected relative decrease in yield for a given evapotranspiration deficit is proportionally greater than the evapotranspiration deficit . The level of accuracy of the crop response factor depends on range and data for yield and evapotranspiration and assumes a linear relationship of the data. Research on identifying the critical stage where water stress can reduce yield and performance of soybean is still in progress. Bustomi Rosadi et al.  investigated the effects of water stress during the vegetative stage of soybeans. They found that the optimal water management of soybean with the highest yield efficiency occurred when the water stress coefficient was 0.80 for the vegetative phase.
Water stress during the reproductive stage has also been found to influence the number and seeds per pod . Water stress at the late reproductive stage accelerated senescence, reduced the seed filling period and pod sizes . Korte et al.  concluded after comparing three irrigations on eight cultivars of soybean that a single irrigation during pod elongation was the most beneficial to soybeans because it increases seeds per plant and irrigation at seed enlargement increases seed weight. Irrigation of soybeans at any stage did not significantly increase yield or only slightly increased the yield above that of non-irrigated treatment if the rainfall is sufficient to supply the water requirement . Karam et al.  investigated the effects of DI at full flowering (R2) stage of soybeans. They reported that DI reduced above-ground biomass and seed yield by 16 and 4%, respectively, and that DI at seed filling at the beginning of seed formation (R5) stage reduced these two parameters by 6 and 28%, respectively. However, they did not investigate economic implications of DI on soybean. Torrion et al.  examined the effects of DI on eight soybean cultivars. They reported that a season-long deficit irrigation strategy significantly reduced the seed yield but they did not evaluate the economic effects of DI. Sincik et al.  investigated the effects of DI on soybeans. They reported that non-irrigated and all deficit irrigation treatments significantly reduced biomass and seed yield and that leaf area indices were significantly reduced at all growth stages. However, they also did not evaluate the economic implications of DI on the crop.
Garcia et al.  investigated the effects of DI regimes on yield and water productivity of different genotypes of soybean. The results showed that DI significantly reduced dry matter, canopy height, and maximum leaf area index. They reported that seed yield increased at a rate of 7.20 kg for every mm of total seasonal water use and that irrigation water productivity (IWP) significantly differed among different genotypes, a feature which can be used as a criterion for achieving greater yields in supplemental irrigation. Gercek et al.  obtained the highest seed yield of soybeans at full irrigation. The highest values of water productivity (WP) and IWP were obtained when 75 and 50% of the full crop water use was applied, while lower total yield was obtained when 50% of the water use was applied.
Water productivity of soybean can be increased by eliminating irrigation at the vegetative stage when evapotranspiration is predominantly by water evaporation from the soil . Reduction in the yield varies from one place to the other where DI is practiced. Environmental and soil factors determine the level of soil water evaporation and availability of water in the soil for plant use. Therefore, there is a need to carry out a comprehensive assessment on the impact of DI on the yield of crops before implementing it as a policy program. This assessment will be used in convincing farmers and other stakeholders on the benefits that may be derived from such approaches.
If drip irrigation is managed properly, it could optimise water use for crop production in addition to other benefits. The objectives of this study were to determine the effects of DI at reproductive stages, by applying a drip irrigation system, on yield components, water productivity (WP), irrigation water productivity (IWP), economic water productivity, and economic returns of soybeans in Ile-Ife, Nigeria. It is located in Ogun-Osun River Basin, southwest of Nigeria.
The study was carried out during the dry seasons of 2013 and 2013/2014 at the teaching and research farms of Obafemi Awolowo University, Ile-Ife, Nigeria. Ile-Ife town is located at latitude 7°28′0″N and longitude 4°34′0″E, 271 m above mean sea level. It is in the sub-humid area of Nigeria. The dry seasons extend from November to March, and the climate is conducive for the cultivation of grains and legumes under total and supplementary irrigation. In the recent times, there is variability in monthly distribution of rainfall in terms of depth, time of occurrence and areal distribution. These fluctuations in the daily rainfall often make it risky to grow crops during the rainy seasons or difficult to make a precise prediction of rainfall contributions to crop water use during dry seasons.
Meteorological data at the weather station in the two seasons (standard deviations in parentheses)
Relative humidity (%)
Global solar radiation (Wm−2)
Irrigation treatments in the two seasons
Irrigation was maintained weekly during all growth stages: flowering (beginning and full bloom), pod initiation (beginning and full pod), seed filling (beginning and full seed) and (beginning and full maturity) maturity stage (reference treatment)
Irrigation was skipped every other week during flowering only
Irrigation was skipped every other week during pod initiation only
Irrigation was skipped every other week during seed filling only
Irrigation was skipped every other week during maturity only
The experimental field was harrowed at the beginning of the fieldwork in both seasons. Force up™ was applied at a rate of 3 L ha−1 on the prepared land to control Heteropogon contortus (L.). The experiment was laid out in a randomized complete block design with three replicates. Due to the dryness of the soil shortly before planting, the field was pre-wetted to a depth of 20 mm in order to initiate seed germination. The cultivar TGX 1448 2E, an indeterminate variety, was planted on February 2, 2013 (first season) and November 8, 2013 (second season). In the first season, delay in the procurement of irrigation equipment coupled with logistic challenges was responsible for the commencement of the experiment in the stated time. Three seeds were sown on flat land at a depth of 4 cm with plant spacing 0.6 by 0.3 m, which produced 55,556 plants ha−1. Each plot contained 68 plants (12 m2) arranged in four rows that is, 17 plants per row. Seedlings were thinned to one plant per stand after full establishment. An alleyway of 1 m was used in separating the plots from each other to allow for easy movement. The area of the field was 19 m by 15 m (285 m2). At the borders of the field, trenches (0.3 m by 0.4 m) were constructed to divert rainwater away from the plots. The inline polyvinyl chloride (PVC) drip pipes (3/4″ Blank Tube) pre-spaced at 0.3 m intervals were arranged in rows and locked (3/4″ EZ lock coupler) at the downstream end of each row to prevent leakage of water. Water locks (3/4″ EZ lock coupler) were placed at the upstream ends of drip pipes to control the application of water. Water was pumped using a gasoline engine (6.5 hp) from a distant stream into an overhead 2,500 L plastic tank (8 m high) and connected through a pipe (1/2″ blank tube) via a water filter (Dripworks, Inc., CA, USA) to the drip lines (rows) in the plots. Water flowed from the overhead tank into the drip lines by gravity.
Insects and beetles were controlled by using Magic Force™ (Jubaili Agro Chemicals) at a rate of 1.5 L ha−1 regularly. The single coefficient approach was used to estimate daily crop water use . After maturity on May 25, 2013 (112 days after planting (DAP)) and February 25, 2014 (110 DAP), an area of 5.37 m2 in the central rows was harvested from each of the plots and the seed yields per ha were estimated.
Dry biomass (DBM)
At intervals of 7 days from 14 DAP in both seasons, the above-ground biomasses were measured from an area of 0.358 m2 in each plot from two replicates. The above-ground biomass was oven-dried at a temperature of 70°C for 48 h until constant weight and the DBM per unit area was estimated. Harvest Index (HI) was determined from the ratio of the mass of the seed yield to that of oven dry biomass .
Design of the drip irrigation system
A pressure-compensating inline drip line (Dripworks, Inc., CA, USA) with emitter capacity of 2.2 L h−1 with operating pressure of 100 kPa was used. Each lateral was 5 m long and contained 17 point inline emitters pre-spaced at intervals of 0.3 m. The volume of water required per plant per day was determined from the ratio of the product of peak evapotranspiration and wetted area occupied by each plant to the emission uniformity. Irrigation frequency was determined from the ratio of the readily available moisture to the peak crop water use. The average amounts of water applied during initial, mid and late stages were 1.13, 6.69 and 3.83 mm day−1, respectively.
Measurement of soil moisture
In the two seasons, the average numbers of weekly irrigations for T1111, T0111, T1011 were 13, 12 and 12, respectively, while for T1101 and T1110, they were 11 and 12 times.
Leaf area index (LAI) and soil evaporation measurement
Above and below photosynthetically active radiation (PAR) and leaf area index (LAI) were measured using an AccuPAR LP 80 (Decagon Devices, Inc., WA, USA) near noon until maturity at average intervals of 7 days from 14 DAP in both seasons. Ten measurements of the above and below PARs were taken from three replicates of each treatment by placing the probe (line sensor) perpendicularly to the rows above and below the plant canopy. The average value of LAIs measured was computed for each of the treatments. A total of 14 consecutive measurements of LAIs was made in each irrigation season. The daily LAI for each treatment was determined by interpolation of the measured values.
Seasonal soil water evaporation (SEP) was determined by summing daily evaporation from emergence until maturity.
Seasonal crop water use (SWU)
In order to determine the crop coefficient factor, the difference (Δ) between the yields for the treatments where irrigation was skipped for 7 days every other week and that of FI was determined. The same procedure was used for the seasonal transpiration (STP).
Economic analysis was done for the two seasons in order to know the profitability of using inline drip irrigation in the cultivation of the crop. The costs of the water tank plus plumbing work, drip lines and accessories and the pumping machine plus PVC hose remained unchanged. The costs of these items were spread over a period of 10 years. The costs of the following items vary from one season to the other due to the economic situation in the area: land preparation, seeds, herbicides, weeding, insecticides, harvesting, threshing and transportation. The researchers hired a plumber to assist in the setting up and coupling of the irrigation accessories. The water pumped from the stream by the researchers themselves was not paid for. The cost of pumping is basically the money spent on petrol and occasional maintenance of the 6.5 hp pumping engine. The cost of pumping water ranged from US$ 987 ha−1 for FI to US$ 675 ha−1 for DI during seed filling. The addition of the costs of all the items above was used to determine the total cost of production for each treatment. Price of the crop was US$ 541 per ton as at the time of harvest . The product of the average seed yields and price per ton gave the total revenue for each treatment. The difference between total cost of production and gross returns gave the financial benefit or loss. English et al.  approach was used in explaining the scenario of water-limiting conditions.
Under the water-limiting situation, land is available but water is limited. In this case, additional land can be brought under irrigation if water is saved by practising DI. The irrigation plan that produces the optimum water and economic water productivity is considered to be the most promising. The trends of WP and IWP among the treatments were compared. The amounts of water saved per unit area during the deficit irrigation treatments and the possibility of increasing the opportunity costs of the irrigation water in the study area were examined. The potential increase in farm income from additional land is an opportunity cost of the water saved during DI.
The statistical software SAS was used for the data analysis. The analyses of variance (ANOVA) of the LAI, seed yields and HI were carried out by using the Duncan Multiple Range Test at significant level α = 0.05 and means were compared.
Results and discussion
Leaf area index and dry biomass
LAI (m2 m−2) during the crop cycle in the two seasons
FL (R1) 49 DAP
PI (R3) 63 DAP
PF (R6) (86 DAP)
MT (R7-R8) (109 DAP)
3.8 ± 0.4a
5.5 ± 0.3a
7.1 ± 0.3a
2.2 ± 0.1a
3.1 ± 0.2ab
4.6 ± 0.2b
4.8 ± 0.4b
0.6 ± 0.3c
2.8 ± 0.2b
4.9 ± 0.3ab
4.2 ± 0.8bc
0.6 ± 0.2c
2.7 ± 0.5b
4.5 ± 0.2b
3.6 ± 0.2c
0.5 ± 0.1c
3.3 ± 0.7ab
4.8 ± 0.6ab
4.5 ± 0.2b
1.4 ± 0.2b
3.4 ± 0.3a
2.6 ± 0.1a
1.3 ± 0.3a
1.0 ± 0.0a
2.4 ± 0.4ab
2.1 ± 0.1b
1.0 ± 0.0a
0.7 ± 0.0d
2.9 ± 0.1abc
2.3 ± 0.2ab
1.1 ± 0.1a
0.8 ± 0.0b
3.2 ± 0.4ab
2.3 ± 0.2ab
1.0 ± 0.0a
0.4 ± 0.0e
2.7 ± 0.0bc
2.5 ± 0.1ab
1.2 ± 0.1a
0.8 ± 0.0c
Seasonal water use, dry matter and seed yield
Growth stages, crop water use (mm) and number of irrigations in the both seasons
Late season (101–112)
Seasonal crop water use (mm)
No. of weekly irrigation
No. of days irrigation was skipped
Relationship between yield decrease and decrease in evapotranspiration
The crop response factor is expressed by the slope of the regression equation. The seasonal ky of 2.24 in this study is higher than 0.85 for soybean under DI . This implies that the moisture stress imposed on the crop was severe and the rate of decrease in seed yield is proportionally higher than the relative deficit SWU. Reduction in the seed yields of soybean is inevitable under DI . In the 2013 irrigation season, yield reductions were 9.3, 25.4, 41.8 and 25.7% (p < 0.05) for T0111, T1011, T1101 and T1110, respectively. Similarly, in the 2013/2014 irrigation season, yield reductions for T0111, T1011, T1101 and T1110 were 28.3, 18.4, 53.9 and 23.0%, respectively. Average seasonal reductions in the seed yields were 18.8 and 21.9% (p > 0.05) for T0111 and T1011 (Table 4). Similarly, average seasonal and significant reductions were 47.9 (p < 0.05) and 24.4% (p > 0.05) for T1101 and T1110. This implies that DI during the seed filling and commencement of maturity in soybeans could lead to a reduction in seed yields by half.
The seed yields for full irrigation in both seasons are significantly higher than those subjected to DI. This result is similar to the findings of Sincik et al.  that non-irrigated and all deficit irrigation treatments significantly reduced biomass and seed yield and yield components. The T test at 95% confidence limit shows that the average seasonal seed yields are significantly different (p < 0.05). The yields of soybean in this study especially for full irrigation and DI compare well with the data in literature. For instance, yields for T1111 are between 3.6 and to 3.7 t ha−1 for fully irrigated soybean and higher than the average seed yields under different DI . The yield range in this study is similar to 2.16–3.93 t ha−1 and 1.98–3.59 t ha−1 for DI irrigation ; 2.3 to 3.5 t ha−1 under different DI  and 2.07 to 3.76 t ha−1 .
Soil water balance
Seasonal evaporation, transpiration, crop water use and seed yields in the two seasons
Yield (t ha−1)
Water productivity and irrigation water productivity
Water productivity, irrigation water productivity and harvest index for full and DI
2013 irrigation season
2013/2014 irrigation season
WP (kg ha mm−1)
IWP (kg ha mm−1)
WP (kg ha mm−1)
IWP (kg ha mm−1)
Water productivity and harvest index
HI reduced significantly (p < 0.05) by 15.1% for T1111, 5.35, and 9.60% for T1011 and T1110, respectively, compared with T0111 in the first season (Table 6). Similarly, HI reduced significantly by 32.4 and 12.2% for T1101 and T0111, respectively, whereas the reductions were 13.3 and 15.0% for T1011 and T1110 in 2013/2014 season. Substantial reduction in HI for T1101 was due to the reduction in STP because of consecutive depletion of the moisture in the root zone, which aborted fruits set, reduced fruit filling and hence reduced the yield. This trend shows that water stress during seed filling can reduce significantly the HI of soybean. Pooled over the years, WP and IWP were significantly correlated with HI (p < 0.05), for WP (SEE = 1.12) and for IWP (SEE = 3.36), respectively. This indicates that HI accounts for 53 and 44% of the variability in WP and IWP, respectively. According to the models, the minimum permissible HIs for the cultivar under investigation were 33.2 and 40.5% for WP and IWP. Improvement in the WPs and IWPs in this study was due to improved HIs under DI. Based on the data, it can be inferred that the cultivar TGX 1448 2E had efficient canopy in producing seeds. Results of this study are in agreement with Neyshabouri and Harfield  and Westgate et al.  who suggested that WP of soybeans could be improved by increasing its HI.
Economic analysis of the use of drip method in cultivating soybean under full and DI conditions
Yield (t ha−1)
Total cost of production ha−1 (US$ × 103)
Total revenue (US$ × 103)
Loss (US$) × 103
Economic productivity (US$ ha−1 mm−1)
Water limited conditions
Average seasonal economic water productivity of 2.42 US$ ha−1 mm−1 under FI was higher than those of T0111, T1110, T1011, and T1101 by 6.7, 19.9, 24.3 and 35.0%, respectively (Table 7). The trend of increase shows that economic water productivity increases with the amount of water due to evapotranspiration. The cost of drip lines and their accessories constituted about 36.9–41.3% of the total cost of production. The skipping of irrigation for 7 days in T0111, T1011 and T1110 reduced the cost of production by 1.33% while the skipping of irrigation for 21 days (T1101) reduced the cost of production by 5.16% compared to T1111.
Shortage of water is often a constraint in crop production especially in dry seasons. In such water-limiting conditions, the water saved by DI can be used to irrigate additional land and thereby increasing farm income [1, 40]. Skipping of irrigation for 7 days every other week during flowering, pod initiation, and maturity conserved about 8.23, 12.2 and 11.4 L of water per m2, respectively. DI for 21 days during seed filling conserved 14.1 L m−2 (141 mm ha−1). It constitutes 22.1% of average SWU for FI to produce 2.31 t ha−1 and 23.7 to 27.5% for DI to produce 1.26–1.96 t ha−1. The water conserved could be used for increasing land productivity for soybeans or for cultivating other crops such as vegetables in addition to soybeans during dry seasons in the study area. Under such conditions, skipping of irrigation during the stated reproductive stages is an appropriate irrigation strategy.
Despite higher yields in T1111, the maximum revenue of US$ 1300 could not provide financial benefit let alone T1101 that received the minimum water in the two seasons (Table 6). This clearly shows that the use of drip irrigation in the cultivation of the crop is not financially sustainable for a peasant farmer despite the spread of the fixed cost over 10 years. A peasant farmer may only benefit from the use of drip lines after several years of continuous cultivation of the crop, adequate maintenance of the facility or if the entire fixed cost is carried by the government or donor agencies. The production of drip lines locally using less expensive and durable materials could reduce the total cost of production during irrigation. The financial benefits at the end of a cropping season depend on strategies used in reducing the cost of production and the available price of the crop in the market.
Assessment of crop water and economic productivity of drip irrigation for soybean was carried out in Ile-Ife during the 2013 and 2013/2014 dry seasons. Results show that deficit irrigation reduced leaf area index, transpiration, number of seeds per plant, seasonal water use and seed yield. Duration of the growth stages and the total number of days in which irrigation was skipped also contributed to the severity of the effects of deficit irrigation on LAI, dry matter, seasonal water use and seed yields. Due to the long period of seed filling (average of 35 days in the two seasons), DI reduced LAI and dry matter such that further application of water during the short period of maturity could not compensate for the reduction and thereby resulted in significant reduction in the seed yield. Although deficit irrigation during flowering and pod initiation reduced LAI, compensation was made after subsequent water application during the season and the effects on the dry matter and seed yield was minimal. Subjection of soybeans to water stress for consecutive 7 days during flowering and total of 21 days during seed filling did not significantly reduce the number of seeds per pod. Peak water productivity was obtained under full irrigation. Water and irrigation water productivity may be increased by skipping irrigation 7 days every other week during pod initiation and commencement of maturity. The water conserved during deficit irrigation could be used to increase opportunity cost. If the primary objective is to increase the seed yield or land productivity of soybeans, full irrigation is hereby recommended. The outcomes of the economic analysis under water-limiting conditions provide information for policy makers at basin scale for formulating improved and efficient water management plans under similar weather conditions. The results will be beneficial in adopting deficit irrigation in a manner that will improve crop water and economic productivity on local and international scales.
irrigation water productivity
day of the year
day after planting
photosynthetically active radiation
leaf area index
seasonal evaporation from soil
seasonal water use
irrigation water applied
analysis of variance
standard error of estimate
OB wrote the proposal and designed the experiment, carried out the field work, analysed, interpreted the data collected from the field and wrote the manuscript. BS coordinated and did oversee the entire research activities, participated in the design, corrected the proposal, and revised the manuscript. KO participated in the design, revised the proposal, supervised the field work in Nigeria, and corrected the manuscript. KC revised the proposal and corrected the manuscript. All authors read and approved the final manuscript.
We would like to thank Prof. O.O. Jegede of the Department of Physics, Obafemi Awolowo University, Nigeria for sharing meteorological data with us and Mr. A. Jejelola of the Institute for Agricultural Research and Training (IAR&T) Ibadan, Obafemi Awolowo University House Station for providing technical assistance during the fieldwork. We are sincerely grateful to Dutch government under Netherlands Fellowship Programme (NFP) for providing the funding for this project. We would also like to thank the reviewer and editors of the journal for their constructive and objective criticisms and suggestions for improvement of the manuscript.
Compliance with ethical guidelines
Competing interests The authors declare that they have no competing interests.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
- English MJ, Musick JT, Murty VV (1990) Deficit irrigation. In: Hoffman GJ, Towell TA, Solomon KH (eds) Management of farm irrigation systems. St. Joseph, MichiganGoogle Scholar
- Pereira LS, Oweis T, Zairi A (2002) Irrigation management under water scarcity. Agric Water Manage 57:175–206View ArticleGoogle Scholar
- Kirda C (2002) Deficit irrigation scheduling based on plant growth stages showing water stress tolerance. Food and Agricultural Organization of the United Nations, Deficit Irrigation Practices, Water Reports, 22, 102
- Zhang J, Sui X, Li B, Su B, Li J, Zhou D (1998) An improved water-use efficiency for winter wheat grown under reduced irrigation. Field Crops Res 59:91–98View ArticleGoogle Scholar
- Specht JE, Elmore RW, Eisenhauer DE, Klocke NW (1989) Growth stage scheduling criteria for sprinkler-irrigated soybeans. Irrig Sci 10:99–111View ArticleGoogle Scholar
- Stegman EC, Schatz BG, Gardner JC (1990) Yield sensitivities of short season soybeans to irrigation management. Irrig Sci 11:111–119View ArticleGoogle Scholar
- Steduto P, Hsiao TC, Fereres E, Raes D (2012) Crop yield response to water, FAO Irrigation and Drainage Paper No, 66, pp 124–131
- Bustomi Rosadi RA, Afandi, Senge M, Ito K, Adomako J (2007) The effect of water stress in regulated deficit irrigation on soybean yield (Glycine max [L.] Merr.). Paddy Water Environ 5:163–169View ArticleGoogle Scholar
- Momen NN, Carlson RE, Shaw RH, Arjmand O (1979) Moisture-stress effects on the yield components of two soybean cultivars. Agron J 71:86–90View ArticleGoogle Scholar
- Brevedan RE, Egli DB (2003) Short periods of water stress during seed filling, leaf senescence, and yield of soybean. Crop Sci 43:2083–2088View ArticleGoogle Scholar
- Korte LL, Williams JH, Specht JE, Sorensen RC (1983) Irrigation of soybean genotypes during reproductive ontogeny. I. Agronomic responses. Crop Sci 23(52):1–527Google Scholar
- Huck MG, Peterson CM, Hoogenboom G, Bush CD (1986) Distribution of dry matter between shoots and roots of irrigated and non-irrigated soybeans. Agron J 78:807–813View ArticleGoogle Scholar
- Karam F, Masaad R, Sfeir T, Mounzer O, Rouphael Y (2005) Evapotranspiration and seed yield of field grown soybean under deficit irrigation conditions. Agric Water Manage 75:226–244View ArticleGoogle Scholar
- Torrion JA, Setiyono TD, Graef GL, Cassman KG, Irmak S, Specht JE (2014) Soybean irrigation management: Agronomic impacts of deferred, deficit, and full-season strategies. Crop Sci 54:2782–2795View ArticleGoogle Scholar
- Sincik M, Candogan BN, Demirtas C, Büyükcangaz H, Yazgan S, Göksoy AT (2008) Deficit irrigation of soyabean [Glycine max (L.) Merr.] in a sub-humid climate. J Agron Crop Sci 194:200–205View ArticleGoogle Scholar
- Garcia y Garcia A, Persson T, Guerra LC, Hoogenboom G (2010) Response of soybean genotypes to different irrigation regimes in a humid region of the southeastern USA. Agric. Water Manage. 97:981–987View ArticleGoogle Scholar
- Gercek S Boydak E, Okant M, Dikilitas M (2009) Water pillow irrigation compared to furrow irrigation for soybean production in a semi-arid area. Agric Water Manage 96:87–92View ArticleGoogle Scholar
- Allen RG, Pereira LS, Raes D, Smith M (1998) Crop Evapotranspiration: Guidelines for computing crop water requirements, FAO Irrigation and Drainage Paper No. 56, Food and Agriculture Organization (FAO). Land and Water Development Division, Rome, p 326Google Scholar
- Siahpoosh MR, Dehghanian E (2012) Water use efficiency, transpiration efficiency, and uptake efficiency of wheat during drought. Agron J 104:1238–1243View ArticleGoogle Scholar
- Ali MH (2010) Fundamentals of irrigation and on-farm water management, vol 1. Springer Science, New York, p 578View ArticleGoogle Scholar
- Cooper PJM, Keatinge JDH, Hughes G (1983) Crop evapotranspiration—a technique for calculation of its components by field measurements. Field Crops Res 7:299–312View ArticleGoogle Scholar
- Lu X, Jin M, van Genuchten MT, Wang B (2011) Groundwater recharge at five representative sites in the Hebei Plain China. Groundwater 49:286–294View ArticleGoogle Scholar
- Araya A, Habtu S, Hadgu KM, Kebede A, Dejene T (2010) Test of AquaCrop model in simulating biomass and yield of water deficient and irrigated barley (Hordeum vulgare). Agric Water Manage 97:1838–1846View ArticleGoogle Scholar
- Lovelli S, Perniola M, Ferrara A, Di Tommaso T (2007) Yield response factor to water (Ky) and water use efficiency of Carthamus tinctorius L. and Solanum melongena L. Agric Water Manage 92:73–80View ArticleGoogle Scholar
- Zhang H, Owie T (1999) Water-yield relations and optima irrigation scheduling of wheat in the Mediterranean region. Agric Water Manage 38:195–211View ArticleGoogle Scholar
- Igbadun HE, Mahoo HF, Tarimo AKPR, Salim BA (2006) Crop water productivity of an irrigated maize crop in Mkoji sub-catchment of the Great Ruaha River Basin Tanzania. Agric Water Manage 85:141–150View ArticleGoogle Scholar
- Food and Agricultural Organization of the United Nations (FAO): FAO food price index, at http://www.fao.org/worldfoodsituation/foodpricesindex/en/2014. Accessed 20th Jun 2014
- Egli DB (2005) Flowering, pod set and reproductive success in soya bean. J Agron Crop Sci 191:283–291View ArticleGoogle Scholar
- Nielsen DC (1990) Scheduling irrigations for soybeans with the Crop Water Stress Index (CWSI). Field Crops Res. 23:103–116View ArticleGoogle Scholar
- Doorenbos J, Kassam AH (1979) Yield response to water: FAO Irrigation and Drainage Paper No. 33, Rome, p 193
- De Costa WAJM, Shanmugathasan KN (2002) Physiology of yield determination of soybean (Glycine max (L.) Merr.) under different irrigation regimes in the sub-humid zone of Sri Lanka. Field Crops Res 75:23–35View ArticleGoogle Scholar
- Dogan E, Kirnak H, Copur O (2007) Effect of seasonal water stress on soybean and site specific evaluation of CROPGRO-Soybean model under semi-arid climatic conditions. Agric Water Manage 90:56–62View ArticleGoogle Scholar
- Candogan BN, Sincik M, Buyukcangaz H, Demirtas C, Goksoy AT, Yazgan S (2013) Yield, quality and crop water stress index relationships for deficit-irrigated Soybean [Glycine max (L.) Merr.] in sub-humid climatic conditions. Agric Water Manage 118:113–121View ArticleGoogle Scholar
- Lamm FR, Abou Kheira AA, Trooien TP (2010) Sunflower, soybean and grain sorghum crop production as affected by drip line depth, Am Soc Agri Biol Eng 26:873–882, ISSN 0883-8542
- Liu S, Zhang XY, Yang J, Drury CF (2013) Effect of conservation and conventional tillage on soil water storage, water use efficiency and productivity of corn and soybean in Northeast China. Acta Agriculturae Scandinavica Section B-Soil Plant Sci 63:383–394View ArticleGoogle Scholar
- Howell TA, Cuenca RH, Solomon KH (1990.) Crop yield response. In: Hoffman GJ et al (eds.), Management of Farm Irrigation Systems. Am. Soc. Agric. Eng (ASAE) St. Joseph, MI, pp 93–122
- Neyshabouri MR, Hatfield JL (1986) Soil water deficit effects on semi-determinate and indeterminate soybean growth and yield. Field Crops Res 15:73–84View ArticleGoogle Scholar
- Westgate ME, Whitgham K, Purcell L (2004) Soybean. In: Wringley C (ed) Encyclopaedia of grain science 2004, Elsevier, New York, pp 146–155
- Oweis T, Hachum A (2006) Water harvesting and supplemental irrigation for improved water productivity of dry farming systems in West Asia and North Africa. Agric Water Manage 80:57–73View ArticleGoogle Scholar
- Geerts S, Raes D (2009) Deficit irrigation as an on-farm strategy to maximize crop water productivity in dry areas. Agric Water Manage 96:1275–1284View ArticleGoogle Scholar