Evapotranspiration Water Use Efficiency Research Articles

Effects of plant spacing on evapotranspiration for estimating crop coefficient of Japonica rice

A field experiment was conducted to evaluate the evapotranspiration (ET), crop coefficient (Kc), and water use efficiency (WUE) of rice in two unique transplanting systems: Jejer Manten (JM) and Jajar Legowo (JL) under irrigated conditions. Research studies in Indonesia attribute JM and JL with high yields and water productivity compared to the conventional tile (TL) system using Indica rice. There is no scientific research on the effect of JM and JL on ET for estimating Kc in both Indica and Japonica rice. The aim of the study is to evaluate the influence of JM, JL, and TL on ET, Kc, and WUE of Japonica rice at different rice growth stages. Crop ET and water surface evaporation beneath the rice canopy (Ew) were measured by lysimeters installed in each transplanting system. The average of Kc was calculated at the vegetative, reproductive, and ripening stages. The yield was higher in JM and JL compared to TL. In terms of water conservation and efficiency, JL outperforms JM and TL due to lower ET, Kc values, and higher WUE. Selecting an appropriate transplanting system is subject to local conditions and water availability .

Simulating drought tolerance of peanut varieties by maintaining photosynthesis under water deficit

Over two-third of global peanuts are grown mainly in seasonally rainfed regions across arid and semi-arid zones where drought is a major yield limiting factor. Breeders are targeting drought adaptive traits by selecting high yielding genotypes under water-limited environments. Recently, several peanut varieties have been developed that exhibit drought tolerant characteristics. Crop models can be used to simulate the impact of these traits for different environments. The overall goal of this study was to develop an approach to simulate drought tolerant traits using the CROPGRO-Peanut model and assess the long-term yield response to these desired traits. Four peanut varieties and one advanced breeding line variety with varying degrees of drought tolerance response were grown under both field and rainout shelter conditions in 2019 and 2020. The trait of maintaining photosynthesis under water deficit was observed in the rainout shelter experiments and incorporated into the crop model as a new drought tolerance cultivar coefficient. The evaluation results with independent data showed that the modified model simulated peanut growth and yield under water-limited conditions reasonably well. The rainfed yield, seasonal evapotranspiration (ET), and grain water use efficiency (WUE) were simulated for both drought tolerant and baseline peanut varieties at two representative sites using weather data from 1998 to 2020. The drought tolerant mechanism of maintaining photosynthesis under water deficit was shown to be an advantageous trait for peanut varieties, which produced higher simulated rainfed yield with enhanced seasonal ET and grain WUE, especially for dry seasons. The simulated photosynthesis and yield were sensitive to values of the drought tolerant factor over an expected range of values. Further research is needed on other potential drought tolerant mechanisms, such as maintaining nitrogen fixation, pod harvest index and leaf growth under drought.

Maize response to irrigation and nitrogen under center pivot, subsurface drip and furrow irrigation: Water productivity, basal evapotranspiration and yield response factors

Information and data about quantification and comparison of crop water productivity indices for various irrigation levels and methods and nitrogen (N) application timings “simultaneously” under the same conditions do not exist. Unprecedented and extensive field experiments were conducted for maize (Zea mays L.) in 2016 and 2017 under center pivot (CP), subsurface drip irrigation (SDI) and furrow irrigation (FI) methods with full irrigation treatment (FIT), 80 % FIT, 60 % FIT and rainfed treatment (RFT) with three N application timings. N treatments were: (i) traditional (TN), (ii) non-traditional-1 (NT-1) and (iii) non-traditional-2 (NT-2). Irrigation-yield production functions (IYPF); evapotranspiration-yield production functions (ETYPF), basal evapotranspiration (ETb), crop water productivity (CWP), irrigation water use efficiency (IWUE); evapotranspiration water use efficiency (ETWUE) and yield response factors (Ky) were quantified for each treatment and irrigation method. SDI method required the least seasonal irrigation amount in achieving maximum yield, followed by CP (>~30 mm more than SDI) and FI (>~55 mm more than SDI). Average crop water requirement for achieving maximum grain yield varied among the N treatments within and between the irrigation methods. Irrigation amounts for achieving maximum yields were about 160, 175 and 175 mm in TN, NT-1 and NT-2 nitrogen treatments, respectively, in the CP method; 130, 150 and 150 mm in TN, NT-1 and NT-2 nitrogen treatments, respectively, in the SDI method; and 184 mm in TN management in the FI method. The highest grain yield production per 25.4 mm of applied irrigation followed the order of CP-TN (2.07 Mg ha−1)>SDI-NT-2 (1.91 Mg ha−1)>FI-TN (1.22 Mg ha−1). Across all treatments for the given irrigation method, the highest averaged CWP of 3.00 kg m−3 (slope = 0.067 kg m−3) was observed in the SDI method (p < 0.05) followed by 2.84 kg m−3 (slope = 0.052 kg m−3) in the CP method (p < 0.05) and 2.51 kg m−3 (slope = 0.046 kg m−3) in the FI method. The lowest ETb was observed in FI-TN (169 mm), followed by CP-NT-2 (172 mm) and SDI-TN (255 mm). For two consecutive years, N treatments did not have significant (p > 0.05) influence on IWUE in the CP or SDI methods. The highest IWUE, CWP and ETWUE were always obtained with limited irrigation treatments (60 % FIT and/or 80 % FIT) whereas the lowest with FIT. Maize under limited irrigation management had Ky < 1 with CP, SDI and FI along with lower Ky values than the respective TN treatment in CP and SDI, suggesting that the yield reduction is impacted to a lesser degree from the magnitude of water stress. The overall conclusion disclosed that utilizing the combination of limited irrigation (80 % FIT) with NT-1 fertigation under SDI and CP, while 80 % FIT under FI can be viable management practices for achieving high grain yield and CWP in conditions similar to those presented in this research.

Fine Soil Texture Is Conducive to Crop Productivity and Nitrogen Retention in Irrigated Cropland in a Desert-Oasis Ecotone, Northwest China

Agricultural production in oases requires extensive irrigation and nitrogen (N) inputs, which result in a high incidence of non-point-source pollution. Information on how soil texture affects crop productivity and water and N use efficiency is needed to improve N management in oases. A two-year field study with six free-draining leaching pits was set up to quantify soil water content (SWC), drainage, yield, N uptake, soil residual N, N leaching, water-use efficiency (WUE), and N fertilizer-use efficiency (NFUE) on sandy-textured soils in a young oasis field (24 years, YOF) and loam-textured soils in an old oasis field (&gt;60 years; OOF) within an intensive oasis agricultural zone in Northwest China. The results showed that sand content in the YOF was significantly higher than that in the OOF (p &lt; 0.01), while both clay and silt contents in the YOF were significantly lower than those in the OOF (p &lt; 0.01). Soil water storage (SW) in the 0–100 cm soil layer, evapotranspiration water-use efficiency (WUEET) and irrigation water-use efficiency (WUEIrrig) in the OOF were, respectively, 87.1, 23.5, and 24.1% higher than those in the YOF (p &lt; 0.05), and deep drainage in the YOF was 6.2 times higher than that in the OOF (p &lt; 0.01). Maize N uptake and soil N accumulation in the OOF in the 0–100 cm soil layer were, respectively, 33.4 and 10.3% higher than those in the YOF (p &lt; 0.05), and N leaching loss in the YOF was 1.65 times higher than that in the OOF (p &gt; 0.01). Crop yield and NFUE in the OOF were, respectively, 23.9 and 27.2% higher than those in the YOF (p &lt; 0.05). These results indicated that sandy-textured soils with high sand content were not conducive to water and N retention, resulting in lower crop yields and water- and fertilizer-use efficiency in YOF. Therefore, it is imperative that management practices in sandy-textured land promote improvements in soil structure and maintain the long-term productivity of the young cultivated fields.

Long-Term Winter Wheat (Triticum aestivum L.) Seasonal Irrigation Amount, Evapotranspiration, Yield, and Water Productivity under Semiarid Climate

A long-term field experiment was conducted from 2002 to 2014 for the evaluation of yield and water productivity of three winter wheat varieties&mdash;Kharkof, Scout 66, and TAM107&mdash;under sprinkler irrigation at New Mexico State University Agricultural Science Center at Farmington, NM. Winter wheat daily evapotranspiration was estimated following the United Nations Food and Agriculture Organization FAO crop coefficient approach (ETc = Kc ETo), and crop water use efficiency (CWUE), evapotranspiration water use efficiency (ETWUE), and irrigation water use efficiency (IWUE) were estimated for each growing season. There was inter-annual variation in seasonal precipitation and irrigation amounts. Seasonal irrigation amounts varied from 511 to 787 mm and the total water supply varied from 590 to 894 mm with precipitation representing a range of 7.7&ndash;24.2%. Winter wheat daily actual evapotranspiration (ETc) varied from 0.1 to 14.5 mm/day, averaging 2.7 mm/day during the winter wheat growing seasons, and the seasonal evapotranspiration varied from 625 to 890 mm. Grain yield was dependent on winter wheat variety, decreased with years, and varied from 1843.1 to 7085.7 kg/ha. TAM107 obtained the highest grain yield. Winter wheat CWUE, IWUE, and ETWUE were also varietal dependent and varied from 0.22 to 1.01 kg/m3, from 0.26 to 1.17 kg/m3, and from 0.29 to 0.92 kg/m3, respectively. CWUE linearly decreased with seasonal water, and IWUE linearly decreased with seasonal irrigation amount, while CWUE, IWUE, and ETWUE were positively correlated with the grain yield for the three winter wheat varieties, with R2 &ge; 0.85 for CWUE, R2 &ge; 0.69 for IWUE, and R2 &ge; 0.89 for ETWUE. The results of this study can serve as guidelines for winter wheat production in the semiarid Four Corners regions. Additional research need to be conducted for optimizing winter wheat irrigation management relative to planting date and fertilization management to reduce the yield gap between winter wheat actual yield and the national average yield.

Crop Evapotranspiration, Irrigation Water Requirement and Water Productivity of Maize from Meteorological Data under Semiarid Climate

Under the semiarid climate of the Southwest United States, accurate estimation of crop water use is important for water management and planning under conservation agriculture. The objectives of this study were to estimate maize water use and water productivity in the Four Corners region of New Mexico. Maize was grown under full irrigation during the 2011, 2012, 2013, 2014 and 2017 seasons at the Agricultural Science Center at Farmington (NM). Seasonal amounts of applied irrigation varied from 576.6 to 1051.6 mm and averaged 837.7 mm and the total water supply varied from 693.4 to 1140.5 mm. Maize actual evapotranspiration was estimated using locally developed crop coefficient curve and the tabulated United Nations Food and Agriculture Organization (FAO) crop coefficients, and from this maize water productivity was determined. Maize actual daily evapotranspiration (ETa) varied from 0.23 to 10.2 mm and the seasonal ETa varied with year and ranged from 634.2 to 697.7 mm averaging 665.3 mm by the local Kc curve, from 687.3 to 739.3 mm averaging 717.8 mm by the non-adjusted FAO Kc values, and from 715.8 to 779.6 mm averaging 754.9 mm with the FAO adjusted Kc values. Maize irrigation requirements varied from 758.4 to 848.3 mm and averaged 800.2 mm using the local developed Kc and varied from 835.5 to 935.6 mm and averaged 912.2 mm using FAO Kc. The net irrigation requirement varied from 606.8 to 678.6 using local Kc curve, and from 682.78 to 748.5 mm when adopting the FAO Kc values. Average irrigation requirement was 641 mm under the local Kc option and 730 mm under FAO Kc values option. Maize crop water use efficiency (CWUE) ranged from 1.3 to 1.9 kg/m3 and averaged 1.53 kg/m3, evapotranspiration water use efficiency (ETWUE) values were higher than CWUE and varied from 2.0 to 2.3 kg/m3, averaging 2.1 kg/m3. Maize irrigation water use efficiency (IWUE) was varied with years and averaged 1.74 kg/m3. There were strong relationships between maize CWUE and maize seasonal irrigation amounts of IWUE and the seasonal irrigation amounts with R2 of 0.97 and 0.92, respectively. Maize CWUE increased linearly with maize IWUE with a coefficient of determination R2 of 0.99, while IWUE showed a strong quadratic relationship with ETWUE (R2 = 0.94). The results of this study can be used as a guideline for maize water management under the semiarid conditions in northwestern New Mexico and other locations with similar climate and management conditions. Irrigation requirements for maize should be adjusted to the local meteorological conditions for optimizing maize irrigation requirement and improving maize water productivity.

Evapotranspiration, Grain Yield, and Water Productivity of Spring Oat (Avena sativa L.) under Semiarid Climate

Spring oat (Avena sativa) is produced for grain, hay, and green manure and can be integrated into a cropping system as a cover crop. Twenty-eight oat genotypes (G1, G2, G3, …., G28), selected for their adaptability to the Southwestern United States, were evaluated for their yield performance under sprinkler irrigation during four growing seasons (2005-2008) at the Agricultural Science Center at Farmington, New Mexico State University. The genotypes were arranged in randomized complete blocs design with four replications. Irrigation scheduling was based on evapotranspiration and the depletion criterion of 40% to 45% total available water (TAW) was practiced to prevent the plants from experiencing any water stress. Crop evapotranspiration estimated by the FAO crop coefficient and reference evapotranspiration approach was low about 2 mm/day during crop initial stage and increased with plant growth and reached the maximum during crop mid-season or reproductive stage. It decreased during crop late season. Daily crop evapotranspiration varied from 0.5 to 12.6 mm in 2008 and the seasonal Spring oat evapotranspiration varied from 535.8 to 591 mm. Averaged across the four growing seasons, oat evapotranspiration was 570.4 mm. The results showed that Spring oat plant height varied significantly with genotypes and ranged from 59.1 to 100.8 cm. Oat grain yield significantly varied with years and genotypes. Grain yield varied from 3386 to 6498 kg/ha and average yield was 4245, 4265, 5477, and 4025 kg/ha during the 2005, 2006, 2007 and 2008, respectively. The best performing genotypes were G1, G2, G7, G19, G20, G21 and G23 with average yield greater than 4800 kg/ha while G3, G13, G17 and G27 showed the lowest yield among the genotypes. Oat crop water use efficiency (CWUE) varied with genotype and years and ranged from 0.53 to 1.07 kg/m3 and averaged 0.65, 0.78, 0.91 and 0.70 kg/m3 in 2005, 2006, 2007 and 2008, respectively. The highest CWUE was achieved by G19 and the lowest CWUE was obtained by G13. Irrigation water use efficiency (IWUE) which represents the quantity of yield produced per cubic meter of water, varied from 0.57 to 1.20 kg/m3 while evapotranspiration water use efficiency (ETWUE) varied with genotype and year and ranged from 0.57 to 1.21 kg/m3 with the overall IWUE mean of 0.83 kg/m3 and ETWUE mean of 0.81 kg/m3.

Large-Scale and Long-Term Trends and Magnitudes in Irrigated and Rainfed Maize and Soybean Water Productivity: Grain Yield and Evapotranspiration Frequency, Crop Water Use Efficiency, and Production Functions

<abstract><title><italic>Abstract.</italic></title> Large-scale quantification and mapping of crop water use efficiency (CWUE), evapotranspiration water use efficiency (ETWUE), and crop yield production functions, especially on a long-term and large-scale basis, are important to effectively evaluate and manage freshwater resources in relation to agricultural production. The overall objectives of this study were to quantify and map the long-term (1986-2009) magnitudes, trends, and frequency distributions of CWUE and ETWUE on a county and statewide scale and develop yield production functions on a county, zonal, and statewide scale for irrigated and rainfed maize and soybean in Nebraska. From 1986 to 2009, total increases of 31%, 37%, 29%, and 33% were observed for irrigated maize, rainfed maize, irrigated soybean, and rainfed soybean yields, respectively. During that period, grain yields increased annually by 166 kg ha^-1 for irrigated maize and by 84 kg ha^-1 for rainfed maize. The yield increases on an annual basis for irrigated and rainfed soybean were about 50 and 30 kg ha^-1, respectively. Irrigated and rainfed maize ET_c peak frequency occurred at 600 and 400 mm, respectively, and irrigated and rainfed soybean ET_c peaks were at 500 and 400 mm, respectively. On average, irrigated maize ET_c was 52%, 46%, 35%, and 25% greater than rainfed maize ET_c in zone 1 (semi-arid), zone 2, zone 3, and zone 4 (sub-humid), respectively. For soybean, irrigated ET_c was 41%, 29%, and 15% higher than rainfed soybean ET_c in zones 2, 3, and 4, respectively (soybean is not grown in zone 1, the driest zone in western Nebraska). Irrigated CWUE for maize for all counties (90 counties for a 24-year period) had a mean value of 1.74 kg m^-3 [standard deviation (SD) = 0.37 kg m^-3] and ranged from 2.07 kg m^-3 in sub-humid zone 4 to 1.33 kg m^-3 in semi-arid zone 1. For soybean, the statewide average (78 counties for a 24-year period) irrigated CWUE was 0.64 kg m^-3 (SD = 0.14 kg m^-3) and ranged from 0.81 to 0.54 kg m^-3. The ETWUE had a mean of 2.32 kg m^-3 (SD = 0.52 kg m^-3) for maize and a mean of 1.01 kg m^-3 (SD = 0.55 kg m^-3) for soybean. On a statewide average basis, about 74% and 3% of the variability in rainfed and irrigated maize yields, respectively, was explained by ET_c alone. For rainfed soybean, ET_c explained about 44% of the variability in yield; however, no strong relationship was observed between irrigated soybean yield and ET_c. Maize CWUE showed substantial increases (from 1986 to 2009) of 35% and 36% in zones 1 and 2, and lesser increases of 17% and 15% were observed in zones 3 and 4, indicating that zones with smaller yields could increase CWUE more effectively by proper irrigation, soil, and crop management. These wide variations in CWUE and ETWUE indicate that there is a significant potential to increase the efficiency of current Nebraska crop production systems. The CWUE and ETWUE maps and the zonal and statewide average yield production function data presented in this study can be useful for evaluating the differences in these variables across the state for close monitoring, assessment, resource allocation, and management decisions.

Interannual Variation in Long-Term Center Pivot–Irrigated Maize Evapotranspiration and Various Water Productivity Response Indices. II: Irrigation Water Use Efficiency, Crop WUE, Evapotranspiration WUE, Irrigation-Evapotranspiration Use Efficiency, and Precipitation Use Efficiency

AbstractQuantification of various water use efficiency (crop water productivity) indices for different irrigation regimes can aid in making effective in-season water management decisions and developing crop water productivity models. However, these critical variables can be affected by interannual variation in climatic conditions, and long-term research that provides such data and information is extremely rare. Maize (Zea mays L.) irrigation water use efficiency (IWUE), crop water use efficiency (CWUE), evapotranspiration water use efficiency (ETWUE), annual precipitation use efficiency (ANNPUE), growing season precipitation use efficiency (GRSPUE), and the newly developed growing season precipitation use efficiency with respect to rainfed yield (GRSPUErainfed) were measured under full and limited irrigation and rainfed conditions from 2005 to 2010 in south-central Nebraska. An additional new irrigation efficiency term [irrigation-evapotranspiration use efficiency (IRRETUE)] was developed and tested to ev...

Soybean Yield, Evapotranspiration, Water Productivity, and Soil Water Extraction Response to Subsurface Drip Irrigation and Fertigation

Abstract. Soybean [Glycine max (L.) Merr.] yield, irrigation water use efficiency (IWUE), crop water use efficiency (CWUE), evapotranspiration water use efficiency (ETWUE), and soil water extraction response to eleven treatments of full, limited, or delayed irrigation versus a rainfed control were investigated using a subsurface drip irrigation (SDI) system at a research site in south-central Nebraska. The SDI system laterals were 0.40 m deep in every other row middle of 0.76 m spaced plant rows. Actual evapotranspiration (ET a ) was quantified in all treatments and used to schedule irrigation events on a 100% ET a replacement basis in all but three of the eleven treatments (i.e., 75% ET a replacement was used in two, and 60% ET a replacement was used in one). The irrigation amount (I a ) applied at each event was 100% of the ET a amount, except for two 100% ET a treatments in which only 65% or 50% of the water needed to cover the treatment plot area was applied to enable a test of a partial surface area-based irrigation approach. The first irrigation event was delayed until soybean stage R3 (begin pod) in two 100% I a treatments, but thereafter they were irrigated with either 100% or 75% ET a replacement. Two 100% ET a and 100% I a treatments also were used to evaluate soybean response to nitrogen (N) application methods (i.e., a preplant method versus N injection using the SDI system). Soybean ET a varied from 452 mm for the rainfed treatment to 600 mm (30% greater) for the fully irrigated treatment (100% ET a and 100% I a ) in 2007, and from 473 to 579 mm (20% greater) for the same treatments, respectively, in 2008. Among the irrigated treatments, 100% ET a and 65% I a had the lowest 2007 ET a value (557 mm), whereas 100% ET a and 50% I a had the lowest 2008 ET a (498 mm). The 100%, 75%, and 60% ET a treatments with 100% I a had respective actual ET a values that declined linearly in 2008 (i.e., 579, 538, and 498 mm), but not in 2007. Seasonal totals for ET a versus I a exhibited a linear relationship (R 2 = 0.68 in 2007 and R 2 = 0.67 in 2008). Irrigation enhanced soybean yields from rainfed yield baselines of 4.04 ton ha -1 in 2007 and 4.82 ton ha -1 in 2008) to a maximum of 4.94 ton ha -1 attained in 2007 with the delay to R3 irrigation treatment (its yield was significantly greater, p -1 attained in 2008 with the 100% ET a and 100% I a preplant N treatment. Seed yield had a quadratic relationship with irrigation water applied and a linear relationship with ET a that was stronger in the drier year of 2007. Each 25.4 mm incremental increase in seasonal irrigation water applied increased soybean yield by 0.323 ton ha -1 (beyond the intercept) in 2007 and by 0.037 ton ha -1 in 2008. Each 25.4 mm increase in ET a generated a yield increase of 0.114 ton ha -1 (beyond the intercept) in 2007, but only 0.02 ton ha -1 in the wetter year of 2008. This research demonstrated that delaying the onset of irrigation until the R3 stage and practicing full irrigation thereafter for soybean grown on silt loam soils resulted in yields (and crop water productivity) that were similar to full-season irrigation scheduling strategies, and this result may be applicable in other regions with edaphic and climatic characteristics similar to those in south-central Nebraska.

Impact of Water and Nitrogen Management Strategies on Maize Yield and Water Productivity Indices under Linear-Move Sprinkler Irrigation

<abstract><title><italic>Abstract.</italic></title> With uncertainty in future irrigation water availability and regulations on nutrient application amounts, experimentally determined effects of “controllable” management strategies such as nitrogen (N), water, and their combination on crop water productivity (CWP, also known as crop water use efficiency) and actual evapotranspiration (ET_a) are essential. The effects of various N application rates (0, 84, 140, 196, and 252 kg ha^-1) under fully irrigated (FIT), limited irrigation (75% FIT), and rainfed conditions on maize (Zea mays L.) yield and various CWP indices were investigated in 2011 and 2012 growing seasons under linear-move sprinkler irrigation in south central Nebraska. CWP was presented as crop water use efficiency (CWUE), irrigation water use efficiency (IWUE), and evapotranspiration water use efficiency (ETWUE). The seasonal rainfall amounts in 2011 and 2012 were 371 mm and 296 mm, respectively, as compared with the long-term average of 469 mm. Two experimental seasons were contrasted with extreme warmer temperatures, greater solar radiation, and lower rainfall in 2012. Maximum grain yield of 12.68 metric tons ha^-1 and 14.42 tons ha^-1 was observed in 2011 and 2012, respectively, under the fully irrigated and 252 kg N ha^-1 treatment. Grain yield was linearly related to ET_a and curvilinearly related to N and irrigation application amounts. Lower N treatments were more susceptible to interannual effects on the grain yield response to irrigation water amount. CWUE ranged from 1.52 kg m^-3 (FIT and 84 kg N ha^-1) to 2.58 kg m^-3 (rainfed and 196 kg N ha^-1) with an average of 2.15 kg m^-3 in 2011, and from 1.49 kg m^-3 (FIT and 0 kg N ha^-1) to 2.72 kg m^-3 (rainfed and 252 kg N ha^-1) with an average of 2.33 kg m^-3 in 2012. CWUE had a positive quadratic relationship with N application amount and decreased with both the presence and amount of irrigation at a given N application amount. The maximum IWUE for 75% FIT and FIT in 2011 was 1.80 kg m^-3 (252 kg N ha^-1) and 1.51 kg m^-3 (252 kg N ha^-1), respectively, whereas in 2012 the maximum IWUE values were 1.40 kg m^-3 (196 kg N ha^-1) and 1.78 kg m^-3 (252 kg N ha^-1), respectively. A curvilinear relationship was observed between IWUE and N application amount. An optimal N application amount of 196 kg ha^-1 was identified for the pooled data to maximize the increase in grain yield above rainfed conditions per unit of applied irrigation water under limited irrigation management practices. In 2011, ETWUE ranged from 0.22 kg m^-3 (140 kg N ha^-1) to 1.46 kg m^-3 (196 kg N ha^-1) and from -0.21 kg m^-3 (84 kg N ha^-1) to 3.74 kg m^-3 (252 kg N ha^-1) for 75% FIT and FIT, respectively, whereas in 2012 ETWUE ranged from -0.07 kg m^-3 (0 kg N ha^-1) to 1.87 kg m^-3 (252 kg N ha^-1) and from -0.14 kg m^-3 (0 kg N ha^-1) to 3.65 kg m^-3 (196 kg N ha^-1) for 75% FIT and FIT, respectively. The results support that there is an optimal N level for each irrigation regime and, in general, lower N application amounts are required to reach maximum productivity (e.g., CWUE) under limited and rainfed conditions as compared with the FIT. In other words, there is an optimal N application amount to maximize the effectiveness of irrigation water on increasing grain yield above rainfed yields. The optimal N level for maximum productivity varied not only between the irrigation levels, but also exhibited interannual variability for the same irrigation level, indicating that these variables are impacted by the climatic conditions.

Soil Water Extraction Patterns and Crop, Irrigation, and Evapotranspiration Water Use Efficiency of Maize under Full and Limited Irrigation and Rainfed Settings

The effects of full and limited irrigation and rainfed maize production practices on soil water extraction and water use efficiencies were investigated in 2009 and 2010 under center-pivot irrigation near Clay Center, Nebraska. Four irrigation regimes (fully irrigated treatment (FIT), 75% FIT, 60% FIT, and 50% FIT) and a rainfed treatment were implemented. The crop water use efficiency (CWUE, or crop water productivity), irrigation water use efficiency (IWUE), and evapotranspiration water use efficiency (ETWUE) were used to evaluate the water productivity performance of each treatment. The seasonal rainfall amounts in 2009 and 2010, respectively, were 426 mm (18% below normal) and 563 mm (9% above normal). Irrigation regime impacted soil water extraction pattern, which increased with irrigation amounts. In general, the soil water extraction decreased with soil depth, and the water extraction from the top soil (0-0.30 m) accounted for the largest portion of the seasonal total water extraction as 39%, 42%, 48%, 48%, and 51% of the total extraction under rainfed, 50% FIT, 60% FIT, 75% FIT, and FIT, respectively. The rainfed treatment extracted more water from the 0.60-0.90 m and 0.90-1.2 m layers (19% and 17% of the total, respectively) than all other treatments. In general, the deepest soil layer (1.5-1.8 m) contributed about 5% to 8% to the seasonal total water extraction. The efficiency values for the same treatments varied between the years due to their dependency on the seasonal water supply, water supply impact on water extraction, climatic conditions, and their impact on yield. The CWUE increased with irrigation from 1.89 kg m-3 for the rainfed treatment to 2.58 kg m-3 for the 60% FIT in 2009 and from 2.03 kg m-3 for the rainfed treatment to 2.44 kg m-3 for the FIT in 2010. The CWUE was strongly correlated to actual crop evapotranspiration (ETa) (R2 = 0.99 in both years), irrigation amounts (R2 = 0.97 in both years), and grain yield (R2 = 0.95 in 2009 and R2 = 0.99 in 2010). The IWUE and ETWUE decreased with ETa and the irrigation amounts in 2009, while they showed the opposite trend in 2010. The IWUE ranged between 3.63 kg m-3 for FIT and 5.9 kg m-3 for 50% FIT in 2009 and between 2.52 kg m-3 for 50% FIT and 3.24 kg m-3 for 75% FIT in 2010. On average, 60% FIT resulted in the largest IWUE of 4.33 kg m-3. The measured ETWUE varied from 4.65 kg m-3 for FIT to 6.09 kg m-3 for 50% FIT in 2009 and from 5.94 kg m-3 for 50% FIT to 6.73 kg m-3 for FIT in 2010. The 60% FIT and 75% FIT had similar or greater CWUE and ETWUE than the FIT in both years. The ETWUE was usually greatest when the ETa was about 580 mm in 2009 and 634 mm in 2010, indicating that in these experimental, climate, and management conditions, the maximum ETWUE and crop water productivity can be obtained at ETa values smaller than those for the fully irrigated treatment. The 60% and 75% FIT treatments were very comparable to the fully irrigated treatment in terms of productivity performance and are viable supplemental irrigation strategies for increasing crop water productivity of maize while using (withdrawal) 40% or 25% less irrigation water under these experimental, soil and crop management, and climatic conditions.

WATER USE EFFICIENCY OF GREENHOUSE SUMMER SQUASH IN RELATION TO THE METHOD OF CULTURE: SOIL VS. SOILLESS

WATER USE EFFICIENCY OF GREENHOUSE SUMMER SQUASH IN RELATION TO THE METHOD OF CULTURE: SOIL VS. SOILLESS

Optimizing irrigation scheduling for winter wheat in the North China Plain

In the North China Plain (NCP), more than 70% of irrigation water resources are used for winter wheat ( Triticum aestivum L.). A crucial target of groundwater conservation and sustainable crop production is to develop water-saving agriculture, particularly for winter wheat. The purpose of this study was to optimize irrigation scheduling for high wheat yield and water use efficiency (WUE). Field experiments were conducted for three growing seasons at the Wuqiao Experiment Station of China Agriculture University. Eleven, four and six irrigation treatments, consisting of frequency of irrigation (zero to four times) and timing (at raising, jointing, booting, flowering and milking stage), were employed for 1994/95, 1995/96 and 1996/97 seasons, respectively. Available water content (AWC), rain events, soil water use (SWU), evapotranspiration (ET) and grain yield were recorded, and water use efficiency (WUE) and irrigation water use efficiency (IWUE) were calculated. The results showed that after a 75-mm pre-sowing irrigation, soil water content and AWC in the root zone of a 2-m soil profile during sowing were 31.1% (or 90.7% of field capacity) and 16.1%, respectively. Rainfall events were variable and showed a limited impact on AWC. The AWC decreased significantly with the growth of wheat. At the jointing stage no water deficits occurred for all treatments, at the flowering stage water deficits were found only in the rain-fed treatment, and at harvest all treatments had moderate to severe soil water deficits. The SWU in the 2-m soil profile was negatively related to the irrigation water volume, i.e. applying 75 mm irrigation reduced SWU by 28.2 mm. Regression analyses showed that relationships between ET and grain yield or WUE could be described by quadratic functions. Grain yield and WUE reached their maximum values of 7423 kg/ha and 1.645 kg/m 3 at the ET rate of 509 and 382 mm, respectively. IWUE was negatively correlated with irrigated water volume. From the above results, three irrigation schedules: (1) pre-sowing irrigation only, (2) pre-sowing irrigation + irrigation at jointing or booting stage, and (3) pre-sowing irrigation + irrigations at jointing and flowering stages were identified and recommended for practical winter wheat production in the NCP.