Water Table Regime Research Articles

Watertable control indices for drainage of agricultural land in humid climates

Annual and seasonal watertable regimes of agricultural land have in many cases succesfully been related to drainage objectives characterising these regimes by such indices as average watertable depths, duration and frequencies of occurrence of high watertables, etc. The merits and applicability of these indices have been analysed in this paper.

Argillic Horizon Expression and Classification in the Soils of Two Michigan Hydrosequences

AbstractTwo hydrosequences in central Michigan were investigated to evaluate the degree of Bt horizon expression as influenced by the depth and duration of soil saturation. Each hydrosequence was sampled in duplicate and consisted of well or moderately well, somewhat poorly, and poorly drained soils. Total clay ratios, I/E indices (fine clay/total clay of the illuvial zone divided the fine clay/total clay of the eluvial zone), and argillan development were greatest in the well‐drained soils and decreased with decreasing depth to and increasing duration of soil saturation. One of the poorly drained soils lacked Bt horizons while one had Bt horizon expression similar to that of the somewhat poorly drained soils. The water table regimes of all poorly drained soils were similar. The poorly drained soils with Bt horizons contained relatively large amounts of smectite, particularly in the clay films, while those lacking Bt horizons contained virtually no smectite. The Bt horizons developed to a greater degree where moisture fronts penetrated the solum the greater period of the year. Where penetration was retarded by soil saturation, mineralogy contributed to the degree of Bt horizon development.

Mobility and Uptake by Plants of Elements Placed Near a Shallow Water Table Interface

AbstractThe water table interface is the transition between unsaturated, usually aerated, soil and water‐saturated, often anaerobic soil. Plant roots may approach this transition zone and absorb elements soluble in and below the transition zone. To examine this possibility, we studied elements that differ in solubility as a function of oxidation‐reduction potential. Barley (Hordeum vulgare cv. Conquest) was grown in field lysimeters, and treatments included various elements (iron, technetium and uranium plus phosphorus), element placement depths, and water table regimes. Measurements included plant uptake of each element, plant root distribution, and soil profiles of total and extractable amounts of each study element and related elements. The transition from aerobic to anaerobic conditions occurred −10 cm above the water table interface. The mobility of the elements decreased in the order Tc > U > P ≥ Fe. The redox gradient markedly modified the mobility of Tc and U. The Fe was more soluble in the reducing environment than in the oxidizing environment, but no migration of Fe was detected. The plant roots were almost entirely confined to the oxidized layers of soil. The plants absorbed no treatment Fe, very little treatment P and U (from the shallow placement only), but substantial amounts of Tc. A fluctuating water table further restricted plant uptake. The water table interface markedly changed the mobility of some of the study elements but the effect on rooting depth was more profound. Thus, the water table interface did not present a unique condition for plant roots to absorb elements as the elements diffused upward from the reducing environment.

Comparative Study of Green and Ampt Analysis for a Falling Water Table in a Homogeneous Sand Profile

Equations are developed for a Green and Ampt type analysis for a falling water table regime in an initially saturated homogeneous profile of porous material both with and without the presence of an applied surface flux of constant magnitude. The predictive capability of these Green and Ampt equations for a homogeneous medium sand is then tested against results obtained from a computer‐based numerical analysis of the differential equation describing water movement in unsaturated porous media. Three simulations with different rates of water table fall are described for the zero surface flux case with one of these rates also being used when an applied surface infiltration flux is included in the system. Comparisons with Green and Ampt results are then made for these simulations in terms of the discharge‐time relationship, the position of the draining front with time, and the thickness of the draining capillary fringe with time. In certain cases the approximate analysis is shown to agree with the numerical simulations quite satisfactorily while in others, notably those involving a more rapid water table fall, the differences are significant.

Response of nine soybean lines to soil moisture conditions close to saturation

The effects of two constant water table treatments, maintained at 3 and 15 cm below the soil surface (CWT 3 and CWT 15, respectively), were compared with the effect of overhead irrigation (OHI) on dry matter production of nine soybean (Glycine max) lines, grown for 36 days in beds of soil in the glasshouse. The lines represented a range of maturity groups. Water for each irrigation treatment was supplied with, or without, dissolved inorganic nitrogen (100 ppm N), on a split plot basis. CWT 15 plants accumulated 37% more dry matter, and 35 times more nodule dry matter, than did OH1 plants. CWT 3 plants became very chlorotic within a week of imposing the water table, but recovered to produce only 18% less dry matter than the OHI plants. CWT 3 plants accumulated the greatest amount of nodule dry matter, and this fraction accounted for 5% of total plant dry weight in some lines. Plants in both of the water table regimes were taller than the OHI plants, even for lines that flowered in 21 days, and this effect reduced the cultural disadvantage of short stature normally noted in early flowering lines. Nitrogen application marginally increased shoot proportion, plant height and node number, but decreased nodule mass in CWT 15 and OHI plants. The study indicated that soybeans can respond well to permanent water tables maintained close to the soil surface, and attain rapid early growth independent of applied nitrogen. Projections suggest that high yields of seed are feasible in 80-85 day soybean crops growing on a controlled water table system. This system also may promote other operational efficiencies related to a shortened cropping cycle, simplified water management, and weed control.

SOIL SALINITY REDUCED BY SUMMER FALLOW AND CROP RESIDUES

Soil salinity can frequently be reduced and controlled under dryland conditions of the Northern Plains by proper use of dryland cultural practices that promote soil water conservation. Summer fallow significantly reduced salinity in the root zone, whereas salinity increased under a small grain crop. Soil salinity reductions attributed to fallow were greater under a deeper water table regime compared to more shallow water table conditions. A straw cover or small grain stubble mulch during the winter, in conjunction with summer fallow, led to further salinity reductions. The straw mulch was more effective in reducing salinity at a more severely saline and higher water table site than at a more moderate location. Summer fallow was more effective at the more moderate site compared to the severe location. Under the combination of summer fallow and winter vegetative mulch, precipitation in excess of evapotranspiration losses supplied water for leaching. Growing a crop, except during high rainfall periods, did not leave excess water. Our findings suggest that summer fallow with winter vegetative residue management can be effectively utilized in the cultural rotation for reducing soil salinity under dryland conditions.

Soil Morphology and Water Table Relations: II. Correlation Between Annual Water Table Fluctuations and Profile Features

AbstractThe frequency of occurrence of water tables at certain depths below the soil surface and the length of time water tables remained at or above these depths were calculated on the basis of rainfall records from a 29‐year period. Results were correlated with soil morphological features.Faint and distinct mottling correlated with water table behavior. The average depth below the surface to the midpoint of the uppermost mottled horizon increased as the drainage condition of the series improved. At the depth of a given degree of mottling, the percentage of time a soil was submerged was essentially the same in a given month for all series. Color designations of Munsell value and chroma for dry crushed material were also correlated with the percentage of time a soil was submerged during the first 6 months of the year. The relations were not consistent for all soils within the drainage sequence, but the poorly‐drained Dayton and Concord soils had the highest values and lowest chromas.Munsell hues of 10YR occurred in horizons of well‐drained soils, whereas Munsell hues of 2.5Y and 5Y occurred in horizons of poorly‐drained soils. The size and abundance of iron and manganese concretions increased in a consistent manner in the sequence from well‐drained to poorly‐drained soils. The sequence of bleached A2 horizons over “clay pan” IIB2t horizons was specifically related to the perched water tables of the Dayton and Concord series.Attempts to isolate relationships between water table regimes and a single color feature of the soil which might be useful as a tool for quantitatively appraising water table regimes were not successful. However, when color features were considered jointly, the morphological assessment of natural drainage class was found consistent with the water table regimes of the soils. The results illustrate the relationship between morphological indicators of soil drainage and water table regimes under climatic conditions peculiar to the Pacific Northwest.

Soil Morphology and Water Table Relations: I. Annual Water Table Fluctuations

AbstractWater table positions with respect to the soil surface and precipitation were measured daily over a 2‐year period at representative sites of five soil series comprising the Willamette association of nearly level soils with good to poor natural drainage. All soils had water tables present for some period during the winter. Perched water tables were present near the surface of the two most poorly‐drained series most of the winter.A mathematical model was developed for predicting water table positions on the basis of rainfall input and soil physical characteristics. The model was calibrated with measurements made during the 2 years and then used with rainfall data from the previous 29 years, to reconstruct water table positions as they had occurred in the past. The computer procedure did not apply to the two poorly‐drained series because of the presence of an impermeable soil horizon (clay B) near the surface. However, water table positions of these series were estimated satisfactorily by correlation with water table positions on the better‐drained series. The average percent of time the water table was above a given level during each month, calculated for the period of 1929 to 1957 showed that for a specific depth and month, the percent of time the water table was above a given level increased as the natural drainage conditions became poorer. The percentages for the 30.4‐cm depth during April for example were 1.8, 15.4, 66.7, 81.5, and 92.0, respectively, for the five series. Thus, particular water table regimes are associated with drainage conditions of specific soil series.

The edge effect in some ultisols in the North Carolina coastal plain

The soil landscape in the middle Coastal Plain of central North Carolina is gently undulating. It has many abrupt to gradual changes in soil drainage that cause corresponding changes in soil texture. These textural changes are not related to textural variation of the original sediment. These changes in soil texture are produced by eluviation from the A2 or the B2 horizons. This eluviation is related to water table regimes. The area of greatest evluviation from the A2 is at the dissected edge of a flat to gently undulating surface where the water table is relatively deep. The area of greatest eluviation from the upper B2 horizon is in the transitional zone between the moderately well- and poorly drained soils where there is a relatively high but fluctuating water table.