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.     

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.     

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.     

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.     

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.     

A soil-climate index to predict corn yield

Rainfall-soil storage (RAINSTOR) equations were developed and refined by fitting various combinations of RAINSTOR against measured corn yield. Separate equations are needed to reflect both water stress (droughty and ponding) conditions. The most limiting value (maximum stress) was used in the calculation of RAINSTOR index values. The RAINSTOR index is a good parameter for predicting corn yield on nearly level soils in the udic moisture regime of New York State. The initial correlation analyses showed a marginal relationship between rainfall and corn yield (r² = 0·13). After using the rainfall-soil storage equations, the RAINSTOR versus corn yield relationship dramatically improved (r² = 0·80). The RAINSTOR equation was tested at two additional sites and the r² was equal to 0·61 and 0·70, respectively.     

A preliminary study on scheduling irrigation with can evaporimeters

Irrigation scheduling was carried out for wheat and maize grown in a semi-arid region, using cumulative pan evaporation (CPE). Scheduling of 60 mm depth of irrigation when CPE was 60 mm ($\text{IW}\text{CPE}\text{= 1.00}$) was found to be optimum for wheat, while 60 mm depth of irrigation when CPE was 50 mm ($\text{IW}\text{CPE}\text{= 1.20}$) was found to be optimum for maize. Cumulative evaporation from 1 l ‘Cans’ (CCE), exposed above these crops, was recorded simultaneously. The ratios $\text{CCE}\text{CPE}$ were found to increase with the advance of the season. The ratios were higher over maize than over wheat.The CCE during the different stages of crop growth varied from 60.6 to 69.0 mm in wheat and from 51.5 to 94.0 mm in maize.     

An Investigation into the Soil Mechanics of Land Anchors

Prediction equations are developed and evaluated to estimate the maximum sustainable pull and the form of penetration of landd anchors. The theories for estimating the pattern of penetration and maximum sustainable anchor force compare well with the measured results in five contrasting soil conditions. The maximum and mean error between the predicted and measured maximum anchor force were 13% and 8%, respectively, representing an over-prediction of force in both cases. The correlation coefficient between the maximum anchor force and the mean values of soil shear strength, obtained using the cone index and shear vane were 0·86 and 0·85 respectively indicating that both the cone penetrometer and shear vane are valuable for in-field prediction of maximum anchor forces in both dry frictional and plastic clay soils.     

Estimation of Moisture Diffusivity Coefficient and Thermal Properties of Alfalfa Pellets

Heat and mass transfer characteristics of alfalfa pellets are needed in the optimization of coolers for freshly-made pellets and in managing storage schedules of the pellets in silos and bins. Moisture diffusivity and thermal properties are important parameters used to characterize the heat and mass transfer ability of a material. In this study, experimental thin-layer data on (a) moisture desorption, (b) moisture absorption and (c) rate of heating of alfalfa pellets were collected. By applying the inverse theory and using second order mass transfer and heat transfer equations in cylindrical coordinates, the moisture absorption and desorption data were used to estimate the moisture diffusivity as a function of moisture content of the pellets while the heating rate data were used to estimate the thermal properties (thermal conductivity and specific heat) as a function of pellet temperature.Better estimates were obtained when moisture diffusivity of the pellets was exponentially related to moisture content in comparison with a linear relation between moisture diffusivity and moisture content. Moisture diffusivity during desorption (2·40×10^-9to 4·12×10^-9 m²/s) was about three times that of the values of diffusivity during moisture absorption (7·50×10^-10to 1·26×10^-9 m²/s). A good fit to the experimental heating rate data was obtained when thermal conductivity and specific heat of the pellets were linearly related to temperature. Over a temperature range of 2 to 110°C, estimated particle thermal conductivities and specific heats of the pellets were in the range of 0·04 to 0·19 W/m K and from 962 to 2114 J/kg K respectively.     

Effect of Peat on the Compactibility of Some Trinidadian Soils

The effect on compactibility of incorporating peat into four Trinidadian agricultural soils before compaction was investigated in a laboratory experiment. A factorial experiment was used to study the effect of peat applied at four levels (0, 4, 8 and 12% by mass) on the maximum dry bulk density (MDBD) and optimum moisture content (OMC) of the four soils (two sandy loams, clay loam and clay) compacted using 5, 15 and 25 Proctor hammer blows. The compaction tests were carried out at different moisture contents which varied according to the values of the plastic limits of the soils.Results showed that while the mean values of MDBD of the soils declined significantly (p = 0.001) from 1·51 to 0·92 Mg m^-3 with increasing peat content, the mean values of OMC increased from 24·2 to 42·6%. While MDBD increased, OMC decreased with increasing compaction levels. This applied to all the soils tested. The clay soils had significantly lower values of MDBD and greater values of OMC than the sandy loam soils. There were significant interaction effects between soil type and level of added peat and between compaction level and level of added peat. These interactions were used to describe the effect of peat on soil compactibility. Multiple linear regression equations based on compactive effort, sand content, clay content and percentage peat content, were generated for predicting values of MDBD and those of OMC of compaction of the soils used in this study. There was reasonable agreement between the equation for predicting MDBD and a similar equation derived for Nigerian soils in previous work. A good negative relationship obtained between MDBD and OMC is also similar to the one derived from previous research.     

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.     

Thermal properties of gram

Values of specific heat, thermal conductivity and thermal diffusivity of rewetted whole grain were found. The specific heat of the grain shows a nonlinear relationship both with temperature and moisture content in the range of 292 to 308 K and 12·4 to 32·4% d.b. respectively, resulting in a second-order multiple regression equation. Bulk thermal conductivity increases both with increase in temperature and moisture content in the ranges 283 to 312 K and 11·5 to 27·2% respectively and was found to vary from 0·114 to 0·247 W/m K. Thermal diffusivity increases with increase in moisture content and decreases with increase in temperature in the temperature and moisture ranges of 293 to 307 K and 12·5 to 26·5% respectively, and its value lies between 9·46 × 10⁻⁸ to 16·35 × 10⁻⁸ m²/s.     

Shallow flow of water through non-submerged vegetation

The shallow movement of water flowing through dense crops of wheat was studied for different crop densities and sowing patterns and ages. The common application of Manning's equation to such flows is shown to be inadequate, particularly since the flows can be described as mixed rather than turbulent.The more general discharge-depth equation has advantages for coping with the conditions, and relevant values of the parameters are provided both for (slope)^0·5 as well as for a suggested (slope)^0·35