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Drainage is an essential land-management practice for growing crops in the Lower Mississippi Valley and Gulf coastal areas. Current crop production and water-management methods pose significant pot...

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.

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.

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.

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.

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.

OXIDATION reduction potentials were measured using platinum electrodes to estimate soil aeration on Mhoon silty clay loam soil planted to sugarcane. Using an Eh of 332 mV as the threshold value below which reduced soil conditions may cause crop damage, the number of days that Eh was < 332 mV was determin-ed for three soil flooding durations, two constant water tables, and one continuously drained treatment. These treatments were imposed on plots 40 m2 in size by flooding three times each summer in 1972 and 1973 on two plots each for 1-, 2-, and 4-wk duration followed by draining to 150-cm depth for 7-, 6-, and 4-wk, respec-tively. Constant water tables were maintained in two plots each at 30 and 120 cm below the soil surface while two plots were drained continuously. Correlating the total number of days Eh was < 332 mV each year with crop yields showed that cane yields decreased 0.2 t/ha and 0.3 t/ha in 1972 and 1973, respectively, for each day Eh was < 332 mV. Sugar yields decreased 28 kg/ha for each day Eh < mV in 1973. The maximum rate that Eh decreased during the various flooding treatments was 67 mV/day. This rate was used to estimate that 4 days were required for the soil to change from an oxidized (600 mV) state to a reduced (332 mV) state. This was also an estimate of how quickly this particular saturated soil must be drained to avoid a decline in sugarcane yields due to poor aeration

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.

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.

AN experiment was conducted on a 10-ha tract of Commerce silt loam in St. James Parish, Louisiana during 1977-1980 to determine the response of sugarcane to subsurface drainage. Cane yields from a drained tract were compared to those from an undrained tract to estimate yield response. Cane yields were increased 3 of 4 years. The value of the increased cane yields was enough to pay for a subsurface drainage system at todays cane prices and drain installation costs..

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.

THREE water management systems were installed on a 7-ha tract of Commerce silt loam soil in Assumption Parish, LA in 1983 and 1984 to determine if the water table could be managed on a field size area and to determine sugarcane response to water management. Each system consisted of closely spaced (15 m) subsurface drain lines that were connected to a water control sump which had facilities for removing water for drainage or adding water for sub irrigation. Land adjacent to the tract on which the water management systems were installed, was used as a check. Rainfall during the three-year experiment was near normal, 1,528 mm, except in 1985 when rainfall was 211 mm below normal. The soil and the crop responded favorably to water table management. In 1985, the systems were particularly useful for subirrigation during the summer drought. Sugar yields were 875, 1,656, and 1,321 kg/ha more than those in the check in 1984, 1985, and 1986, respectively. At 1987 sugar prices and drain installation cost estimates, these yield increases were more than enough to make annual payments on a water management system, excluding loan interest and tax credits. Crop production efficiency was enhanced since the amount of sugar produced by the area without water management, could be produced with 18% less land if water management were used.

SIX years of data from erosion plots at Holly Springs, MS, and 10 yr of data from plots at Morris, MN, were used to study variation in soil erodibility through the year. Monthly values of soil erodibility were related to time with a cosine curve. Erodibility varied from a high of 169% of annual average K (K of the Universal Soil Loss Equation) on February 4 to a low of 31% of annual average on August 5 for the Mississippi data. Minnesota erodibility data were described similarly except the maximum and minimum of the erodibility function lagged the Mississippi curve by about 2 months. It was suggested that erodibility could be predicted using a variability function based on normal air temperature data described by a cosine function and average annual K factor values.