Cade E. Carter

THE INFLUENCE OF SUBSURFACE DRAINAGE PRACTICES ON HERBICIDE LOSSES

ABSTRACT Atrazine and metolachlor were applied preemergent on 22 April 1987, to silage corn on high watertable fields which were either subsurface drained (104 mm drain tubes 1 m deep) or surface drained only. Surface runoff and subsurface outflow were sampled and analyzed for atrazine and metolachlor from 22 April to 31 August 1987. Subsurface drainage reduced atrazine and metolachlor losses by 55 and 51%, respectively. Two-thirds of the losses occurred within 30 days after the application of the herbicides, and most of the losses were in the surface runoff. The edge-of-field average atrazine concentrations, 12.5 and 9.0 ug/1, for the non-drained and drained fields, respectively, were four and three times greater than the U.S. Environmental Protection Agency advisory of 3 ug/1 for drinking water. The edge-of-field average metolachlor concentrations were near the U.S. EPA advisory of 10 ug/1.

VARIABILITY OF AUGER HOLE HYDRAULIC CONDUCTIVITY VALUES FOR A COMMERCE SILT LOAM

ABSTRACT Saturated hydraulic conductivity (Ks) values measured from auger holes spaced 6.1 m apart in twenty-six 300 m transects were analyzed for spati^d variability. Hole depths from 0.6 to 2.4 m in 0.3 m increments with water table depths from near 0 to 1.0 m were used in this study. The same auger hole was normally used for several depths by first digging the hole to the shallowest depth and then successively increasing the depth in 30 cm increments. A capacitance system was used to measure the rate of water rise in the auger holes at depths to 2.1 m whereas a resistance tape system was used for depths >2.1 m. Spatial variability analyses showed significant spatial structure for several transects and little or no structure, i.e. random variation of Kg, for most other transects. However, the removal of the variation caused by the presence of a significant drift in the data sets also removed all apparent spatial structure.

Yield Response of Sugarcane to Stalk Density and Subsurface Drainage Treatments

ABSTRACT Afield experiment was conducted in South Louisiana during 1980-1982 on a 3.24 ha tract of Commerce silt loam soil to determine the yield response of sugarcane to stalk density and subsurface drainage treatments. Four sugarcane planting patterns, each with and without subsurface drainage were as follows: (a) conventional - cane planted in a single V-furrow on seedbeds 1.8 m apart, (b) wide furrow - cane planted in 0.45 m wide furrows on seedbeds 1.8 m apart, (c) triple drill - cane planted in three V-furrows spaced 0.3 m apart on seedbeds 1.8 m apart, and d) 0.6-m V-furrows -cane planted in single V-furrows 0.6 m apart. Each treatment was replicated four times. Three crops were harvested - plant, first ratoon, and second ratoon in 1980, 1981, and 1982, respectively. Yields of sugarcane were significantly different among planting patterns in plant and second ratoon crops but not in the first ratoon. The 0.6 m V-furrow treatment had the highest yield of sugarcane in the plant crop, 124 t/ha, which was 70% more than the conventional V-furrow treatment, and the lowest yield in second ratoon, 38.8 t/ha, which was 30% less than conventional. In a combined analysis using all three years of data, the triple drill treatments had the highest yield of sugarcane among planting patterns, 79.2 t/ha, which was 17% more than the conventional treatment. Sugar yield was significantly different among planting patterns only in the plant crop. Sugar yield from the 0.6 m V-furrow was highest among planting patterns, 14.9 t/ha, which was 55% more than the conventional treatment. Sugarcane yields from undrained plots were significantly lower than those in drained plots in second ratoon and in a combined analysis for the 3-year cycle. Sugarcane yields from drained plots in the second ratoon crop and in the combined analysis were 45% and 10% more, respectively, than yields from the undrained plots. Sugar yields were significantly different due to drainage treatments in second ratoon only, when yields from the drained plots were 26% more than yields from the undrained plots. The rate at which sugarcane yields declined in ratoon crops was slowed by subsurface drainage. Although this experiment showed that non-conventional planting patterns increased yields in the plant crop, additional work is needed on maintaining high yields into first and second ratoons before these new planting practices can be recommended to sugarcane growers. Subsurface drainage should be included in sugarcane production practices to reduce the adverse effects of high water table on sugarcane and sugar yields.

Sump-Controlled Water Table Management Predicted with DRAINMOD

ABSTRACT Fluctuations in depth of the water table midway between subsurface-drainage/subirrigation conduits in a sump-controlled water table management system were predicted within an average deviation of 8 cm in DRAINMOD simulations conducted for a Commerce silt loam soil in the Mississippi Delta. The average daily sump water level from a field experiment was used as a model input to establish changes in the drainage outlet water level boundary conditions.

Drainage Needs as Indicated by High Water Tables

ABSTRACT WATER table depths were measured and SEW30 determined for nondrained and subsurface-drained areas in four South Louisiana Parishes (Counties) during 1979 through 1985 to quantify the water table problem and the need for subsurface drainage. High SEW30 values from the nondrained treatments indicated that a high water table problem occurred frequently in three Parishes and occasionally in the fourth Parish. SEW30 values from the nondrained area were significantly higher than those in the drained area indicating the effectiveness of subsurface drainage in reducing or eliminating the water table problem. Crop response -corn at one site and sugarcane at three sites -was favorable to subsurface drainage as yields from the subsurface-drained areas were significantly higher than those from the nondrained areas

Determination of Saturated Hydraulic Conductivity of a Commerce Silt Loam Soil

ABSTRACT FOUR methods of measuring hydraulic conductivity (K) - soil core, auger hole, double-tube, and drawdown - were evaluated for an alluvial soil in the lower Mississippi Valley. The soil, a Commerce silt loam, fine silty, mixed, non-acid, thermic Aerie Fluvaqent, has a saturated K of approximately 1 mm/h in the layer just below the plow depth and K increases only slightly to a depth of about 0.6 m. Between 0.6 and 1.3 m depth there is a layer of approximately 0.3 m thickness that has a saturated K of up to 80 mm/h. Although K varied considerably, the values were within a range where any one of the four methods tested could be used for estimating hydraulic conductivities provided precautions were taken, such as pressing instead of hammering core sampling rings into the soil.

Productivity of sugarcane on narrow rows, as affected by mechanical harvesting

Richard, E.P. Jr., Dunckelman, J.W. and Carter, C.E., 1991. Productivity of sugarcane on narrow rows, as affected by mechanical harvesting. Field Crops Res., 26: 375-386. The growth-and-yield response of the six major commercial sugarcane (Saccharum interspecific hybrids) cultivars to mechanical culture and harvesting on row-spacings of 0.9, 1.2 or 1.8 m (conventional) was investigated in Louisiana. In the plant-cane crop, millable stalk populations for all cultivars were 32% and 17% greater at the 0.9- and 1.2-m spacings, respectively, compared with the 1.8-m spacing. Differences in stalk populations among row-spacings decreased with successive harvests of the stubble crops. By the second-stubble crop, only the cultivar CP 70-330 continued to show a significant increase in stalk populations at the 0.9-m row-spacing. Whole-stalk mechanical harvesters adapted to the narrower spacings minimized stubble destruction observed in earlier studies, but appeared to be less efficient in gathering and piling stalks for weighing. As a result, standing cane yield (tonnage) responses were similar for all cultivars, and were significantly higher at the 0.9- and 1.2-m spacings only in the plant-cane crop. When standing cane yields were averaged over the crop cycle, significant increases in yield occurred only for CP 65-357 (0.9-m), CP 70-321 ( 1.2 m), and CP 70-330 (0.9 m) when the row spacing was narrowed, indicating that cultivar selection may also affect row-spacing responses under mechanical culture and harvesting conditions.

EFFECTS OF EXCESS SOIL WATER ON SWEET CORN YIELD

ABSTRACT An experiment was conducted on silt loam alluvial soil in Louisiana to determine the yield response of sweet com to excess soil water stress and to determine crop susceptibility factors during vegetative and tasseling/silking stages of growth. Sweet com yield from 40 m2 plots that received excess soil water stress treatments (high water table within 30 cm of the soil surface) of three, six-, and nine-days duration during vegetative and tasseling/silking stages was usually significantly less than yield from the control (drained/irrigated) treatment. Average yield among treatments was lowest from the nine-days stress duration. Yields of sweet corn stressed for nine days during the vegetative and tasseling/silking stages were 77 and 61% less, respectively, than those from the drained/irrigated treatment. Normalized crop susceptibility factors, based on weight of marketable corn, were 0.55 and 0.45 for the vegetative and tasseling/silking stages, respectively. These factors indicate that sweet com is highly susceptible to excess soil water stress during both stages of growth but usually more so during the vegetative stage. Correlating the relative com yield (marketable weight) with Stress Day Index values indicated that relative com yield decreased 0.62% for each one-unit increase in the Stress Day Index. Fifty-four percent of the variation in relative sweet com yields was explained by Stress Day Index.

Corn Silage Response to Subsurface Drainage on Alluvial Soil

ABSTRACT A sub surface drainage experiment on clay loam soil near Baton Rouge, Louisiana, was conducted from 1980-1983. The expeiment consisted of four plots, of which two were both surface and subsurface drained. Corn silage was grown each year. Average yields from the subsurface drained plots were 84% higher than the yields from plots with surface drainage only. The growing season high water table stress as quantified by SEW30 had a highly significant affect on corn silage yields.

COMPARISON OF EROSION PREDICTIONS WITH GLEAMS, GLEAMS-WT, AND GLEAMS-SWAT MODELS FOR ALLUVIAL SOILS

Simulation performances of GLEAMS, GLEAMS-WT, and GLEAMS-SWAT were evaluated by comparing their soil loss predictions with measured data from two runoff-erosion-drainage experimental plots at Baton Rouge, Louisiana, One of the experimental plots was surface drained only, and the other was both surface and subsurface drained. Although the hydrology components of GLEAMS-WT and GLEAMS-SWAT predicted surface runoff more accurately than the original GLEAMS, all three models seriously underpredicted total soil losses over a seven-year period (1981 to 1987). Transport capacity limited soil loss prediction values in the models. Hence, we recommend that any changes or modifications in the erosion submodel be focused on improving transport capacity simulation; changes in the detachment simulation routine may not be needed. A calibration parameter was added to the erosion subroutine to adjust transport capacity. However, even when the models were calibrated for a specific site, there were still substantial annual and monthly differences between predicted and observed soil losses. Keywords. GLEAMS, Models, Runoff, Erosion.