Simulated ET Research Articles

Optimizing Wheat Water Productivity as Affected by Irrigation and Fertilizer-nitrogen Regimes in an Arid Environment

The present study evaluated the applicability of the CropSyst model under variable climatic, irrigation, and fertilizer-nitrogen regimes. The objective was to analyze wheat productivity responses to water and N-application for optimizing water productivity in an arid irrigated environment. Evaluation analysis showed that the model provided very satisfactory estimates for the emergence, flowering and physiological maturity dates. The performance of the model was reasonable as demonstrated by the close correspondence between simulated grain yield, biomass accumulation, seasonal ET, and irrigation water productivity (WPI) with measured data. The normalized root mean square error ranged between 5 and 10% for most of the parameters. Overall, the Willmott index of agreement between simulated and observed values of grain yield, biomass and seasonal ET were 0.99, 0.98 and 0.97, respectively. The validated model was employed to assess interactive effects of irrigation and fertilizer N on grain yield and water productivity indices. Scenario analyses indicated that WPI and WPET (ET water productivity) ranged from 0.16 to 2.07 kg m -3 , and from 0.07 to 1.49 kg m -3 , respectively. For predicting the best N and water application practices for maximization of water productivity, the best option found by the model was application of water and nitrogenous fertilizer in 70% and 90% of the required values, respectively, for WPI, and equal to the required values (100%) for WPET. The simulations demonstrated that the current wheat productivity of 5.0 Mg ha -1 obtained by the local farmers can be achieved at 140 kg ha -1 fertilizer N and 30% deficit irrigation regime with a WPI of 1.73 kg m -3 . The CropSyst model can be applied to derive best management options in terms of N and irrigation application of wheat under arid conditions.

Analyzing wheat productivity responses to climatic, irrigation and fertilizer-nitrogen regimes in a semi-arid sub-tropical environment using the CERES-Wheat model

In order to enhance crop productivity in water-limited environments, there is a need to evaluate and apply water-saving management practices. This study examined the applicability of the CERES-Wheat model under variable climatic, irrigation, and fertilizer-nitrogen (N) regimes. The objective was to analyze wheat yield responses to water- and N-application for optimizing crop productivity under water limitations in a semi-arid sub-tropical irrigated environment. Evaluation analysis showed that performance of the model was reasonable as indicated by close correspondence of simulated crop phenology, biomass accumulation, grain yield, and soil water and N use with measured data. The normalized root mean square of deviations ranged between 10 and 20% for most of the parameters. Cumulative probability distribution of simulated grain yield and ET showed that for a given irrigation regime, fertilizer N had greater effect on yield than on ET and caused greater water productivity. Scenario analysis also demonstrated that grain yield and water productivity response to irrigation were influenced by extractable water capacity of soils. Soil effects on grain yield were more pronounced under I 0 regime, and the effect decreased with increase in irrigation. Post-sown irrigation was more effective under conditions of low initial soil water. Initial soil mineral-N status influenced the amount of fertilizer N for a given initial soil water and post-sown irrigation scenario.

Integration of MODIS data into a simple model for the spatial distributed simulation of soil water content and evapotranspiration

A precise simulation of soil water content (SWC) and actual evapotranspiration (ET a) in a region or a catchment depends on the accuracy of the spatial data inputs. In this study, we developed a simple grid-based soil water balance model. In this model, remotely sensed vegetation data are used to estimate spatial distributions of daily SWC and ET a rates. The model was validated by comparing simulated SWC with the measured by gravimetric method and time domain reflectometry (TDR) at an experimental test site located in Northeastern Germany in the time period 1993–1998. The index of agreement IA and the root-mean-square error obtained from the comparison of the TDR measurements to the simulated values ranged from 0.45 to 0.80 and from 0.029 to 0.061 cm 3/cm 3, respectively. The comparison of simulated ET a rates to those measured by four large-scale lysimeters at another test site showed IA values above 0.87 and R 2 values higher than 0.59. For the regional application of the model, a method was developed to integrate the Moderate Resolution Imaging Spectrometer (MODIS) vegetation data into the model. The MODIS data used in our study consist of 16-day normalized difference vegetation index and 8-day leaf area index products. Regarding the spatial application of the model, our approach was tested in a catchment located in Northeastern Germany in 2001–2003. A sufficient correlation between daily discharge rates measured at two observation gauges in the catchment and the corresponding simulated discharge rates and also good correlations between the simulated ET a rates and the MODIS-leaf area index values indicate that the model is an appropriate simulation tool at regional scale if the corresponding additional spatial databases regarding surface and soil properties are available.

ON-FARM SCHEDULING STUDIES AND CERESMAIZE SIMULATION OF IRRIGATED CORN

A field study was conducted to evaluate an irrigation scheduling model (KanSched) using seven center pivot irrigated corn sites in south central Kansas from 1999 to 2001. Portions of each center pivot irrigation system were modified to apply various irrigation amounts. Site-specific irrigation, weather, and field data were used in KanSched to create comparative irrigation schedules for each test zone of each site. Those schedules were also used in the CERES-Maize corn growth simulation model. Irrigation treatments included deficit amounts ranging from 10 to 180 mm while excess irrigation amounts ranged from 8 to 139 mm. KanSched calculated crop evapotranspiration (ETks) ranged from 370 to 488, 356 to 426, and 386 to 566 mm, while CERES-Maize simulated crop ET ranged from 418 to 585, 398 to 699, and 409 to 712 mm for all sites in 1999, 2000, and 2001, respectively. Analyses of measured corn grain yield versus a KanSched water balance ratio [Rw = (Net irrigation + Effective rain + Soil water depletion) / ETks] indicated that crop yield was highest at a water balance ratio of 1.0 (full irrigation). Measured yield from all treatments ranged from 9.5 to 13.1, 7.4 to 14.4, and 3.8 to 16.1 Mg ha-1 while CERES-Maize simulated corn yield ranged from 7.9 to 13.8, 6.9 to 17.1, and 6.6 to 13.8 Mg ha-1 in 1999, 2000, and 2001, respectively. In general, substantial deficit irrigation amounts reduced measured grain yield especially in drier years on south central Kansas farm sites. While the CERES-Maize model simulated average yield from all sites and years was equal to the average measured yield, the model over-predicted measured yields in the lower end of the measured yield range and under predicted yield in the upper end of the measured yield range. Thus, the CERES-Maize model may be adequate for large spatial and temporal simulations, but may not be adequate to simulate individual sites and deficit yield conditions.

MEASURED AND SIMULATED EVAPOTRANSPIRATION OF GRAIN SORGHUM GROWN WITH FULL AND LIMITED IRRIGATION IN THREE HIGH PLAINS SOILS

Water conservation in irrigated agriculture of the semiarid Great Plains relies on accurate prediction of cropwater use to gain the greatest benefit from declining irrigation water supplies. One method for estimating crop water useapplies crop specific coefficients to adjust reference evapotranspiration (ETo). We compared daily measuredevapotranspiration (ETm) of limited and fully irrigated grain sorghum to simulated ET (ETc) calculated using single and dualcrop coefficients (Kc) and a grassreferenced ETo. We also compared simulated and actual applied irrigation waterrequirements that were based on full replacement of ET. The dual Kc procedure contained separate coefficients for croptranspiration, soil water evaporation, and water stress, as compared with one coefficient in the single Kc procedure.Shortseason grain sorghum was grown in weighing lysimeters containing monolithic soil cores of Pullman, Ulysses, orAmarillo soil located in a rain shelter facility. With the dual Kc procedure, the difference during the season betweencumulative ETc and ETm varied from 2 mm to around 70 mm, and by the end of the season the maximum difference in alltreatments was about 60 mm, or 10%. The single Kc procedure underestimated final cumulative ETm in the fully irrigatedtreatments by as much as 120 mm. Simulated and actual applied irrigation amounts in the fully irrigated treatments weresimilar using the dual Kc methodology, but the single Kc methodology undersimulated irrigation needs by more than 100 mmin all treatments. The dual Kc procedure improved water use predictions compared with the single Kc procedure.

Simulation of evapotranspiration from groundnut under wet and dry conditions

A diffusion based simulation model was tested on groundnut ( Arachis Hypogaea L) in a lateritic sandy loam soil (Oxic-Haplustalf) of eastern India. Two moisture regimes, wet and dry, were induced by recharging the soil profile (1.2 m depth) to field capacity storage, whenever soil water pressure reached −0.078 m at 0.225 m (wet) and 0.6 m (dry) soil depths, respectively. Moisture retention characteristics and hydraulic conductivity curves were measured for three distinct soil layers of the experimental soil profile. Readily available meteorological, soil and plant data were used as input parameters of the model. The simulated cumulative ET (ET S) closely corresponded with the field observed cumulative ET (ET f) in the early part of the drying cycle following irrigation. However at the later part of the drying cycle ET, deviated from the ETf, this being particularly true under wet regime. The closest match between ET, and ET f was observed under dry soil water regime 50–70 days after sowing (DAS). The model underestimated the field observed ET up to 50 DAS and there after overestimated it.

Monte Carlo simulations of supercoiling free energies for unknotted and trefoil knotted DNAs

A new Monte Carlo (MC) algorithm is proposed for simulating inextensible circular chains with finite twisting and bending rigidity. This new algorithm samples the relevant Riemann volume elements in a uniform manner, when the constraining potential vanishes. Simulations are performed for filaments comprising 170 subunits, each containing approximately 28 bp, which corresponds to a DNA length of 4770 bp. The bending rigidity is chosen to yield a persistence length, P = 500 A, and the intersubunit potential is taken to be a hard-cylinder potential with diameter d = 50 A. This value of d yields the same second virial coefficient as the electrostatic potential obtained by numerical solution of the Poisson-Boltzmann equation for 150 mM salt. Simulations are performed for unknotted circles and also for trefoil knotted circles using two different values of the torsional rigidity, C = (2.0 and 3.0) x 10(-19) dyne cm2. In the case of unknotted circles, the simulated supercoiling free energy varies practically quadratically with linking difference delta l. The simulated twist energy parameter ET, its slope dET/dT, and the mean reduced writhe <w>/delta l for C = 3 x 10(-19) dyne cm2 all agree well with recent simulations for unknotted circles using the polygon-folding algorithm with identical P, d, and C. The simulated ET vs. delta l data for C = 2.0 x 10(-19) dyne cm2 agree rather well with recent experimental data for p30 delta DNA (4752 bp), for which the torsional rigidity, C = 2.07 x 10(-19) dyne cm2, was independently measured. The experimental data for p30 delta are enormously more likely to have arisen from C = 2.0 x 10(-19) than from C = 3.0 x 10(-19) dyne cm2. Serious problems with the reported experimental assessments of ET for pBR322 and their comparison with simulated data are noted. In the case of a trefoil knotted DNA, the simulated value, (ET)tre, exceeds that of the unknotted DNA, (ET)unk, by approximately equal to 1.40-fold at magnitude of delta l = 1.0, but declines to a plateau about 1.09-fold larger than (ET)unk when magnitude of delta l > or = 15. Although the predicted ratio, (ET)tre/(ET)unk approximately equal to 1.40, agrees fairly well with recent experimental measurements on a 5600-bp DNA, the individual measured ET values, like some of those reported for pBR322, are so large that they cannot be simulated using P = 500 A, d = 50 A, and any previous experimental estimate of C.