An analysis of the effect of the vertical fissuring in mole-drained soils on drain performances

Numerical solutions of the seepage equation of groundwater flow were used in an analysis of the effect on drain performance of the herring-bone pattern of vertical fissuring, with fractures fanning out from the central slit, in mole-drained soils. Drain performances were assessed from values of the dimensionless parameter $\text{W}{}_{\mathrm{<mtext>m</mtext>}}\text{=}\text{2E}{}_{\mathrm{<mtext>m</mtext>}}\text{qD}{}^2$, where E_m is the ‘seepage potential’ at the position of maximum water-table height when the steady rainfall is q and the drain spacing is 2D. W_m decreased with increase in the length of the fractures and, to a lesser extent, with decrease in the spacing of them, showing that the fracturing enables a mole-drainage system to cope with higher rainfall rates and to produce more rapid water-table drawdowns.     

Effect of mixed cation solutions on hydraulic soil properties

Hydraulic conductivity (K) and soil water diffusivity (D) characterizing water flow under saturated and unsaturated conditions, respectively, were determined for a sandy loam and a clay loam soil, using water with different combinations of total electrolyte concentrations, C (i.e., 20, 40, 80, 125 and 250 meq 1^?1) and sodium adsorption ratios, SAR (i.e., 0, 20, 30, 40, 80 and ∞ mmole $\text{l}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$). Both K and D were found to increase with C and decrease with SAR. In low sodium adsorption ratio ranges (i.e., up to 20) the requirement of electrolyte concentration to maintain relative hydraulic conductivity = 0.5 was relatively more for sandy loam than for clay loam soil. However, the trend for electrolyte concentration requirements for the two soils was reversed at high sodium adsorption ratios (i.e. > 20). A spline function was used to draw the best fitting line through the data points of horizontal absorption experiments.     

Wheat root distribution,water extraction pattern and grain yield as influenced by time and rate of irrigation

The effect of first irrigation (26, 40 and 54 days after seeding) and the rate of irrigation (5.5, 7.5 and 9.5 cm) applied subsequently at $\text{IW}\text{E}{}_{\mathrm{<mtext>pan</mtext>}}$ ratio of 0.9 on wheat root distribution, water extraction pattern and grain yield was studied on a barrier-free, sandy loam soil. The crop developed a more extensive root system when the first irrigation was applied after 26 days than after 40 and 54 days. With the first irrigation on the 26th day, the crop, receiving subsequent irrigations less frequently but at a heavier rate, developed a deeper root system than the crop receiving frequent, light irrigations. The water extraction pattern corresponded with the root distribution pattern. A relatively small difference in root density in the deeper layers caused a greater difference in soil water content than in the upper layers. Light and frequent irrigations produced maximum grain yields. However, for developing an extensive root system and enhancing water utilization in the subsoil, an early, light irrigation with subsequent irrigations applied less frequently at a relatively heavier rate seems desirable.     

Evaluation of a crop water stress index for irrigation scheduling of bermudagrass

This study was conducted to assess crop water stress index (CWSI) of bermudagrass used widely on the recreational sites of the Mediterranean Region and to study the possibilities of utilization of infrared thermometry to schedule irrigation of bermudagrass. Four different irrigation treatments were examined: 100% (I₁), 75% (I₂), 50% (I₃), and 25% (I₄) of the evaporation measured in a Class A pan. In addition, a non-irrigated treatment was set up to determine CWSI values. The status of soil water content and pressure was monitored using a neutron probe and tensiometers. Meanwhile the canopy temperature of bermudagrass was measured with the infrared thermometry. The empirical method was used to compute the CWSI values. In this study, the visual quality of bermudagrass was monitored seasonally using a color scale. The best visual quality was obtained from I₁ and I₂ treatments. Average seasonal CWSI values were determined as 0.086, 0.102, 0.165, and 0.394 for I₁, I₂, I₃, and I₄ irrigation treatments, respectively, and 0.899 for non-irrigated plot. An empirical non-linear equation, Qave=1+⌊6[1+(4.853 CWSIave)^2.27]^−0.559⌋$Q_{\text{ave}}=1+⌊6{[1+{(4.853\text{CWS}{\text{I}}_{\text{ave}})}^{2.27}]}^{-0.559}⌋$, was deduced by fitting to measured data to find a relation between quality and average seasonal CWSI values. It was concluded that the CWSI could be used as a criterion for irrigation timing of bermudagrass. An acceptable color quality could be sustained seasonally if the CWSI value can be kept about 0.10.     

The effect of organic manuring and water quality on water transmission parameters and sodication of a sandy loam soil

Water transmission characteristics under saturated and unsaturated conditions were studied in a sandy loam soil with (F₁) and without (F₀) long-term farmyard manure (FYM) treatments, in relation to sodium adsorption ratios (SAR) and electrolyte concentrations of water. The effect of FYM and ratios of Ca²⁺ : Mg²⁺ in water at a given SAR on sodication of the soil was also studied.Saturated hydraulic conductivity (k) and weighted mean diffusivity ($\text{D}\text{?}$) were slightly higher for F₁ than for F₀, whereas sodication indices like Gapon constant (K_G), Krishnamoorthy-Davis-Overstreet constant (K_KDO) and Vanselow constant (K_V) were slightly smaller. The k and $\text{D}\text{?}$ decreased with an increase of SAR and decrease of electrolyte concentration, the effect of SAR being more pronounced. There was proportionately a sharper decrease in the k and $\text{D}\text{?}$ values at SAR 10 with total electrolyte concentrations of 10–40 meq 1^?1. However, with a total electrolyte concentration of 80 meq 1^?1, there was a smaller drop at SAR 10.A small difference in the build-up of exchangeable sodium percentage (ESP) in F₁ and F₀ treatments at a given SAR suggests that, apart from slightly improving water transmission parameters, the use of FYM also reduces the sodication hazard in a soil irrigated with sodic waters. An increase in the Ca²⁺ : Mg²⁺ ratio from 25:75 to 75:25 slightly decreased the values of K_G, K_KDO and K_V, thus indicating somewhat more preference for Ca²⁺ to Mg²⁺ at a given SAR, which was more so in F₁ soil. This fact could also be expressed in terms of a slight shift of thermodynamic exchange constant (K) and standard free energy change of the exchange reaction (ΔG⁰_r). The presence of some unidentified Na⁺ releasing minerals in the soils studied was observed and correction for exchangeable Na⁺ determination applied.     

Irrigation planning in cotton through simulation modeling

Experiments were undertaken at CCS Haryana Agricultural University Farm, Sirsa (India) to estimate the optimum irrigation schedule for cotton resulting in minimum percolation losses. The sprinkler line source technique was adopted for creating various irrigation regimes at different crop growth stages. The SWASALT (Simulation of Water And SALT) model after calibration and validation provided water balance components. The wa-ter management response indicators (WMRI's) such as transpiration efficiency E_t/(Irr + P), relative transpiration E_t/E_tp, evapotranspiration efficiency ET/(Irr + P), soil moisture storage change ΔW/W_int (deficit/excess) and percolation loss Perc/(Irr. + P) were evaluated using water balance components as estimated by the simulation study. Under limited water supply conditions, the optimum irrigation depth was found to be 57 mm at crop growth stages with pre-sowing and 1^st irrigation of 120 mm and 80 mm respectively for sandy clay loam underlain by sandy loam soil (Type I). The corresponding values of relative transpiration, transpiration efficiency and evapotranspiration efficiency were 0.65, 0.65 and 0.89 respectively. The crop yield varied linearly with increasing irrigation depth which was evident from increase in relative transpiration with increasing depth of water application. However, increased depth of irrigation resulted in less moisture utilisation from soil storage (20% depletion at 40 mm depth and 4.4% moisture built up at 100 mm depth). The extended simulation study for sandy soil underlain by loamy sand (Type II) indicated that two pre-sowing irrigations each 40 mm and subsequent irrigations of 40 mm at an interval of 20 days depending upon rainfall were optimum. This irrigation scenario resulted in zero percolation loss accompanied by 74% relative transpiration and 14 per cent soil moisture depletion. Received: 20 November 1995     

Evapotranspiration components determined by sap flow and microlysimetry techniques of a vineyard in northwest China: Dynamics and influential factors

Large areas of vineyards have been established in recent years in arid region of northwest China, despite limited water resources. Water to support these vineyards is mainly supplied by irrigation. Accurate estimation of vineyard evapotranspiration (ET) can provide a scientific basis for developing irrigation management. Transpiration and soil evaporation, as two main components of ET, were measured separately in a vineyard in this region by heat balance sap flow system and micro-lysimeters during the growing season of 2009. Diurnal and seasonal dynamics of sap flow and its environmental controls were analyzed. Daily sap flow rate (SR_l) increased linearly with solar radiation (R_s), but showed an exponential increase to its maximum curve as a function of vapor pressure deficit (VPD). Residuals of the two regressions both depended on volumetric soil water content to a depth of 1.0 m (VWC). VWC also significantly influenced SR_l. The relationship of them could be expressed by a piecewise regression with the turnover point of VWC = 0.188 cm³ cm⁻³, which was ∼60% of the field capacity. Conversely, soil evaporation (E_s) increased exponentially with VWC. Thus, we recommended keeping VWC in such vineyards slightly above ∼60% of the field capacity to maintain transpiration while reducing soil evaporation. Vineyard transpiration (T_s) was scaled from sap flow by using leaf area (A_l) as it explained 60% of the spatial variability of sap flow. Vine transpiration was 202.0 mm during the period from April 28 to October 5; while that of E_s was 181.0 mm. The sum of these two components was very close to ET estimated by the Bowen ratio energy balance method (386.9 mm), demonstrating the applicability of sap flow for measuring grape water use in this region.     

Effects of winter wheat row spacing on evapotranpsiration, grain yield and water use efficiency

A field study was conducted from 2002 to 2007 to investigate the influence of row spacing of winter wheat (Triticum aestivum L.) on soil evaporation (E), evapotranspiration (ET), grain production and water use efficiency (WUE) in the North China Plain. The experiment had four row spacing treatments, 7.5 cm, 15 cm, 22.5 cm, and 30 cm, with plots randomly arranged in four replicates. Soil E was measured by micro-lysimeters in three seasons and ET was calculated from measurements of soil profile water depletion, irrigation, and rainfall. The results showed that E increased with row spacing. Compared with the 30-cm row spacing (average E = 112 mm), the reduction in seasonal E averaged 9 mm, 25 mm, and 26 mm for 22.5 cm, 15 cm, and 7.5 cm row spacings, respectively. Crop transpiration (T) increased as row spacing decreased. The seasonal rainfall interception and seasonal ET were relatively unchanged among the treatments. In three out of five seasons, the four different treatments showed similar grain yield, yield components and WUE. We conclude that for winter wheat production in the North China Plain, narrow row spacing reduced soil evaporation, but had minor improvements on grain production and WUE under irrigated conditions with adequate nutrient levels.     

Corn and alfalfa production as influenced by limited irrigation

Summary Several corn and alfalfa varieties were subjected to varying levels of water deficits under field conditions over a two-year period at the Utah State University Evans farm at Logan, Utah. Dry matter yields of corn and alfalfa varieties showed a linear relationship to evapotranspiration (E _t . In most cases grain yields also showed a linear response to E _t . When relative yields of dry matter and grain of corn varieties were related to relative E _t it was found that the slopes of the linear regression lines changed more between the two years than between the varieties within a given year. It was found that yields predicted by Hanks' (1974) model were highly correlated with measured yields for both corn and alfalfa.in coperation with Agric. Exp. StnGraduate student and professor, respectively     

Evapotranspiration predictions: a comparison among GLEAMS,Opus, PRZM-2, and RZWQM models in a humid and thermic climate

Environmental fate models are increasingly used to evaluate potential impacts of agrochemicals on water quality to aid in decision making. However, errors in predicting processes like evapotranspiration (ET), which is rarely measured during model validation studies, can significantly affect predictions of chemical fate and transport. This study compared approaches and predictions for ET by GLEAMS, Opus, PRZM-2, and RZWQM and determined effects of the predicted ET on simulations of other hydrology components. The ET was investigated for 2 years of various fallow–corn growing seasons under sprinkler irrigation. The comparison included annual cumulative daily potential ET (ET_p), actual ET, and partitioning of total ET between soil evaporation (E_s) and crop transpiration (E_t). When measured pan evaporation was used for calculating ET_p (the pan evaporation method), Opus, PRZM-2, and RZWQM predicted 74, 65, and 59%, respectively, of the 10-year average ET reported for a nearby site. When the energy-balance equations were used for calculating ET_p (the combination methods), GLEAMS, Opus, PRZM-2, and RZWQM predicted 84, 105, 60, and 72% of the reported ET, respectively. The pan evaporation method predicted a similar amount of ET to the combination methods for bare soil, but predicted less ET when both E_s and E_t occurred. RZWQM reasonably predicted partitioning of ET to E_s, while GLEAMS and Opus over-predicted this partitioning. A close correlation between soil water storage in the root zone and ET suggests that accurate soil water content predictions were fundamental to ET predictions. ©     

Combined effect of technical, meteorological and agronomical factors on solid-set sprinkler irrigation: I. Irrigation performance and soil water recharge in alfalfa and maize

In this work, maize (Zea mays L.) and alfalfa (Medicago sativa L.) were irrigated in two adjoining plots with the same sprinkler solid-set system. Irrigation was evaluated between four sprinklers in the central position within each plot, above the canopy with pluviometers and in the soil with a FDR probe. Maize and alfalfa were simultaneously irrigated under the same operational and technical conditions during two seasons: in 2005, the solid-set irrigation system layout was rectangular, 15 m between sprinklers along the irrigation line and 15 m among lines (R15 × 15), and the seasonal irrigation applied according to the crop evapotranspiration (ET_c); in 2006, the solid-set layout was R18 × 15 and the seasonal irrigation was around 30% lower than the ET_c. The irrigation depth above the canopies (ID_C) and the soil water recharge after irrigation (RW) were monitored using a 3 m × 3 m grid (25 points in 2005 and in 30 points in 2006). For maize, RW was assessed both in the lines of plants (CL) and between the lines (BCL).The average values of ID_C were similar between crops during both seasons but the uniformity (CUC) of the ID_C noticeably depended on the crop: the differences were greater between crops than between sprinklers spacings (R15 × 15 and R18 × 15). The CUC of ID_C, the RW and the CUC of RW were greater for alfalfa than for maize. The CUC of ID_C was greater than the CUC of RW for both crops. The RW was significantly related with the ID_C throughout the irrigation season for alfalfa. The correlation was weaker for maize, with important differences between positions and between growth stages. At the beginning of the season, the RW significantly correlated with the ID_C, both in the CL and BCL positions. However, the correlation weakened when the maize grew, especially in the CL, because the maize plants redistributed the water.The results show that the height and canopy architecture of the crop must be considered in the analysis of the sprinkler water distribution as factors influencing the irrigation performance.     

Irrigation, tillage and mulching effects on soybean yield and water productivity in relation to soil texture

Depleting groundwater resources in Indian Punjab call for diversifying from rice to crops with low evapo-transpiration needs and adopting water-saving technologies. Soybean offers a diversification option in coarse- to medium-textured soils. However, its productivity in these soils is constrained by high soil mechanical resistance and high soil temperature during early part of the growing season. These constraints can be alleviated through irrigation, deep tillage and straw mulching. This 3-years field study examines the individual and combined effects of irrigation, deep tillage, and straw mulching regimes on soybean yield and water productivity (WP) in relation to soil texture. Combinations of two irrigation regimes viz., full irrigation (I_f), and partial irrigation (I_p) in the main plot; two tillage regimes viz., conventional-till (CT)-soil stirring to 0.10 m depth, and deep tillage (DT)-chiseling down to 0.35 m depth followed by CT in the subplot; and two mulch rates viz., 0 (M₀) and 6 t ha⁻¹ (M) in the sub-subplot on two soils differing in available water capacity were evaluated.Seed yield was greater in the sandy loam than in the loamy sand reflecting the effects of available water capacity. Irrigation effects were greater on loamy sand (40%) than on sandy loam (5%) soil. Deep tillage benefits were also more on loamy sand (14%) compared to sandy loam (5%) soil. Yield gains with mulching were comparable on the two soils (19%). An evaluation of interaction effects showed that mulching response was slightly more in I_p (20%) than in I_f regimes (17%) in the sandy loam; while in the loamy sand, mulching gains were comparable (18-19%) in both irrigation regimes. Benefits of deep tillage in the loamy sand soil were more in I_p (20%) than in I_f regimes (17%). Deep tillage and straw mulching enhanced WP (ratio of seed yield/water use) from 1.39 to 1.97 kg ha⁻¹ mm⁻¹ in I_p regime, and from 1.87 to 2.33 kg ha⁻¹ mm⁻¹ in I_f regime in the loamy sand soil. These effects on WP were less in the sandy loam soil with greater available water capacity. Yield and WP gains are ascribed to deeper and denser rooting due to moderation of soil temperature and water conservation with straw mulching and tillage-induced reduction in soil mechanical resistance. Root mass in CTM₀, CTM, DTM₀ and DTM was 2.79, 5.88, 5.34 and 5.58 mg cm⁻² at pod-filling in the loamy sand soil. Comparable yield responses to deep tillage or mulching in the loamy sand soil suggest that either of the options, depending on their cost and availability considerations, can be employed for improving soybean yield and water productivity.     

Evaluation of DRAINMOD using saturated hydraulic conductivity estimated by a pedotransfer function model

Direct measurement of soil saturated hydraulic conductivity (K_s) is time-consuming and therefore costly. The ROSETTA pedotransfer function model is able to estimate K_s from soil textural data, bulk density and one or two water retention points. This study evaluated the feasibility of running the DRAINMOD field-scale hydrological model with K_s input produced using ROSETTA. A hierarchical approach was adopted to estimate K_s using ROSETTA, with four limited-more extended sets of soil information used as inputs: USDA textural class (H1); texture (H2); texture and bulk density (H3); texture, bulk density, water retention at −33 kPa (θ_33 kPa) and −1500 kPa (θ_1500 kPa) (H4). ROSETTA-estimated K_s values from these four groups (H1-H4) were used in DRAINMOD to simulate drain outflows during a 4-year period from a conventional drainage plot (CD) and two controlled drainage plots (CWT1 and CWT2) located in south-east Sweden. The DRAINMOD results using ROSETTA-estimated K_s values were compared with observed values and with model results using laboratory-measured K_s values (H0). Deviations in simulated drainage outflow (D), infiltration (F) and evapotranspiration (ET) resulting from the use of ROSETTA-estimated rather than laboratory-measured K_s values were evaluated. During the study period, statistical comparisons showed good agreement on a monthly basis between observed and DRAINMOD-simulated drainage rates using five soil datasets (H0, H1, H2, H3 and H4). The monthly mean absolute error (MAE) ranged from 0.57 to 0.82 cm for CD, 0.38 to 0.41 cm for CWT1, and 0.15 to 0.22 cm for CWT2. On a monthly basis, the modified coefficient efficiency (E′) values were in the range of 0.62 to 0.74 for CD, 0.72 to 0.74 for CWT1, and 0.79 to 0.86 for CWT2. The modified index of agreement (d′) for monthly predictions ranged from 0.80 to 0.86 cm for CD, 0.87 to 0.88 cm for CWT1, and 0.89 to 0.93 cm for CWT2. The absolute values of the percent-normalised error (NE) on an overall basis when using ROSETTA-estimated rather than laboratory-measured K_s values were less than 3% in E, less than 1% in F, and less than 15% in D. The results suggest that ROSETTA-estimated K_s values can be used in DRAINMOD to simulate drainage outflows as accurately as laboratory-measured K_s values (H0) in coarse-textured soils.     

Irrigation with brackish water under desert conditions I. Problems and solutions in production of onions (Allium cepa L.)

To identify the problems and suggest solutions for onion production under brackish water irrigation in a desert environment, a series of trials with brackish water (electrical conductivity, EC_i = 4.4 dS/m) and fresh water (EC_i = 1.2 dS/m) was conducted, using both sprinkler and drip irrigation systems.Under sprinkler irrigation with brackish water the mean electrical conductivity of the saturated soil extract ($\text{EC}$_e) was about 6.0 dS/m and the yield reduction was 60%. With drip irrigation, the $\text{EC}$_e under the drippers was about 5.0 dS/m and the yield reduction was 30%. Sprinkler irrigation affected yield through a reduction in both bulb size and bulb number per unit area. Drip irrigation affected the bulb number only. In the latter system seedling death occurred during the first 40 days following field emergence. Yield reduction was completely prevented by germinating and establishing the field with freshwater irrigation before transferring to brackish water irrigation, 45 days after sowing.With the sprinkler system, onion yield with brackish water irrigation could be increased by either increasing the sowing density or by alternating between brackish and fresh water irrigation.