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.     

Water use by alfalfa,maize, and barley as influenced by available soil water

The availability of soil water is one of the most important determinants of crop production. Field studies were conducted to examine the relationships between relative evapotranspiration ($\text{E}\text{E}{}_{\mathrm{<mtext>max</mtext>}}$) and available water (W) for alfalfa, maize, and barley. Line source sprinkler irrigation systems were used to provide the variations in soil moisture. Actual evapotranspiration (E) was determined using the water balance method. Maximum evapotranspiration (E_max) was the highest E observed among all irrigation levels. Potential evapotranspiration (E₀) was estimated using Penman's equation to characterize the evaporative demand.The results show that the relationships between $\text{E}\text{E}{}_{\mathrm{<mtext>max</mtext>}}$ and W were different for the three crops. For alfalfa, the relationship was dependent on the physical properties of the soil and on E₀. In a clay loam soil, the decline in E from E_max commenced at a higher value of W than in a sandy loam soil. Furthermore, the rate of decline in E from E_max was dependent on E₀ and was greater as E₀ increased. In the sandy loam soil, the relationship between $\text{E}\text{E}{}_{\mathrm{<mtext>max</mtext>}}$ and W was not dependent on E₀. For maize and barley in clay loam soils, $\text{E}\text{E}{}_{\mathrm{<mtext>max</mtext>}}$ as a function of W was linear, and was not dependent on E₀. This study was compared to results reported in the literature, and it was hypothesized that differences were related mainly to the way variation in soil moisture was introduced over the measurement period.     

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.     

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.     

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.     

Yield and growth responses of kenaf (Hibiscus cannabinus L.) in a semi-arid tropical environment to irrigation regimes based on leaf water potential

Summary The growth response of kenaf (Hibiscus cannabinus L.) to four irrigation schedules based on leaf water potential _l was evaluated in a semi-arid tropical environment. Total dry matter production was unaffected by regimes in which the mean value of leaf water potential _l (mean of solar noon and dawn value) did not fall below –1.26 MPa. Stem elongation was more sensitive than dry matter accumulation to plant water stress. — The economic yield for paper pulp production (i. e. total plant dry matter production minus that of the foliage and upper 60 cm of stem) increased with the frequency of irrigation. — Growth recovery by kenaf following a period of water stress was examined. Alleviation of water stress 10 weeks after irrigation, when _l was –1.60 MPa, produced stem elongation rates that were greater than those of plants previously receiving irrigation. This ability to withstand water stress and partially compensate in growth following alleviation of the stress indicates that the kenaf crop has stress response features suitable for rainfall only production under semi-arid tropical conditions. — Irrigation schedules based on _l resulted in water applications tailored to crop requirements in that water use increased, and the time interval between irrigation decreased, with increasing canopy development as well as with increasing evaporative demand. However, erratic fluctuations in _l between irrigations make scheduling by this method difficult and the use of daily mean, dawn or noon values of _l for scheduling irrigation of kenaf cannot be recommended in environments of high evaporative demand. The factors contributing to these fluctuations in (_l) are discussed.     

Field evaluation of crop yield as affected by nonuniformity of sprinkler-applied water and fertilizers

The determination of target uniformity for sprinkler irrigation system should consider the impacts of nonuniformity of water and fertilizers on crop yield. Field experiments were therefore conducted in north China plains to address the impacts of nonuniformly applied water and fertilizers on winter wheat yield. Irrigation water and fertilizers were applied through a solid set sprinkler system. Three experimental plots were used with seasonal Christiansen uniformity coefficients (arithmetic mean of individual CUs) ranging from 62 to 82%. Each plot was divided into $\text{3}\text{m}\text{×3}\text{m}$ grids. Sprinkler water depth and concentration of fertilizer solution for each grid was measured both below and above the canopy for each individual irrigation event. The spatial distribution of soil moisture for each experimental plot was also measured periodically to determine irrigation times and amounts. On harvest, grain yield and total nitrogen content of plant stems were measured for each grid. The experimental results showed that the uniformity of fertilizer applied increased with sprinkler water uniformity. The distributions of both fertilizers and water applied through sprinkler system can be represented by a normal distribution function. Field experiments also demonstrated that the uniformity of sprinkler-applied water and fertilizers has insignificant effect on winter wheat yield for the studied uniformity range. The current standard for sprinkler uniformity (for example, the target CU is equal to or higher than 75% in China) is high enough for obtaining a reasonable crop yield in dry sub-humid regions.     

Pressurised irrigation technologies for smallholders in developing countries – a review

The findings of a study of factors influencing the uptake of pressurised irrigation technologies by smallholders in developing countries are presented. The paper reviews the physical and technical characteristics that determine their suitability for use by smallholders. It also identifies a range of pre-conditions relating to water availability, institutional support and economic opportunity that must be satisfied before smallholders will adopt even low-technology pressurised irrigation systems.The review demonstrates that where physical, economic and institutional conditions are right some forms of pressurised modern irrigation technology permit smallholder irrigation of high value crops where surface irrigation would be inappropriate. However, the paper warns against the danger of wide-scale promotion of such technologies without considering the issues of institutional and technical support. Where pressurised systems are promoted to increase water use efficiency it is essential that they be well designed, installed and operated for savings to be realised.     

An improved Lewis-Milne equation for the advance phase of border irrigation

Summary The Lewis-Milne (LM) equation has been widely applied for design of border irrigation systems. This equation is based on the concept of mass conservation while the momentum balance is replaced by the assumption of a constant surface water depth. Although this constant water depth depends on the inflow rate, slope and roughness of the infiltrating surface, no explicit relation has been derived for its estimation. Assuming negligible border slope, the present study theoretically treats the constant depth in the LM equation by utilizing the simple dam-break wave solution along with boundary layer theory. The wave front is analyzed separately from the rest of the advancing water by considering both friction and infiltration effects on the momentum balance. The resulting equations in their general form are too complicated for closed-form solutions. Solutions are therefore given for specialized cases and the mean depth of flow is presented as a function of the initial water depth at the inlet, the surface roughness and the rate of infiltration. The solution is calibrated and tested using experimental data.Abbreviations a (t) advance length - c mean depth in LM equation - c _f friction factor - c _h Chezy's friction coefficient - g acceleration due to gravity - h(x, t) water depth - h ₀ water depth at the upstream end - i() rate of infiltration - f(x, t) discharge - q₀ constant inflow discharge - S _f energy loss gradient or frictional slope - S₀ bed slope - t time - u(x, t) mean velocity along the water depth - x distance - Y() cumulative infiltration - (t) distance separating two flow regions - infiltration opportunity time     

Rapid field evaluation of drip and microspray distribution uniformity

The Cal Poly ITRC irrigation evaluation programs have been widely used to assess the global distribution uniformity (DU) of drip and microsprayer irrigation systems. The field procedures and formulas used in the program are presented in this paper. The system DU is estimated by mathematically combining the component DU values. DU components include pressure differences, other causes (such as manufacturing variation, plugging, and wear), unequal drainage, and unequal application rates. Results are presented from evaluations by several entities, including Cal Poly ITRC. Cal Poly evaluations of 329 fields provided an average DU_lq of 0.85 for drip and 0.80 for microspray. Approximately 45% of the non-uniformity was due to pressure differences, 52% was due to other causes, 1% due to unequal drainage, and 2% due to unequal application rates. The data show that with good design and management, it is possible to have high system DU values for at least a 20-year system life.     

Grain yield,yield components,drought sensitivity and water use efficiency of spring wheat subjected to water stress at various growth stages

Summary The influence of water stress at various growth stages on yield and yield structure of spring wheat (Triticum aestivum, L., cv. Sappo) was investigated using lysimeters in the field, automatically protected from rain by a mobile glass roof. Each drought treatment consisted of a single period without irrigation. Irrigation was resumed when all available soil water (100 mm between field capacity and permanent wilting to a depth of 100 cm) had been used. The drought periods were defined as beginning when relative evapotranspiration decreased below one and ending at reirrigation. The first drought occurred during tillering and jointing and the final one during grain formation.