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The Coastal Plains Soil, Water, and Plant Research Center has been monitoring spatial yield in a test field since 1985, using a conventional corn-wheat-soybean rotation most of that time. Observations of variation in soil and crop response that correlate with yield variation suggest that crop water relations may be the key feature that causes spatial variability in yield for the Southeastern Coastal Plain. Experience with mechanistic modeling indicates that for normal weather years, the final yield is particularly sensitive to variations in soil water, presumably because the surface soil is sandy and rooting volume is limited. These conclusions, plus difficulties encountered in scheduling irrigation under a center pivot on typically variable soils, led the USDA-ARS to desi~n and build a site-specific center pivot capable of differentially irrigating lOO-m areas. A 3-tower commercial center pivot was modified by adding 39 9.2-m manifolds in 13 sections, 3 to a section. The manifolds and nozzles were sized lx, 2x, and 4x, so that octal combinations would provide up to 7x the minimum application depth for a given outer tower speed. At 50% speed, the application depths are 0 to 12.5 mm in 1.8-mm increments. A prograrnrnable controller was attached near the pivot end of the boom, so that it was proximal to but avoided the pivot control panel when the system rotated. The individual manifolds were controlled by a program residing in the progranunable controller, which obtained pivot position and other information via radio modem link with the pivot control panel. Water and nitrogen application has been accomplished using this system on a replicated field experiment. Experience gained during this phase will guide modification of a similar pivot for site-specific water, nutrient, and pesticide management on a typically variable Coastal Plain field.

Availability of spatially-indexed data and crop yield maps has caused increased interest in site-specific management of crop inputs, especially water and fertilizer. As commercial equipment to implement site-specific applications of water and nutrients becomes available, crop response to variable inputs and decision support systems will be required to ensure profitable crop production while conserving natural resources and protecting the environment. The objective of this research was to determine corn yield response to a range of nitrogen fertilizer and irrigation amounts on a relatively uniform southeastern Coastal Plain soil under conservation tillage. Corn was grown in a field experiment using a center pivot irrigation system that had been modified to make site-specific applications of water and fertilizer during the period 1999-2001 on a site near Florence, South Carolina. Treatments included three antecedent crop rotations (prior four years), three irrigation regimes (0, 75%, and 150% of a base rate, IBR), and four nitrogen fertilizer amounts (50%, 75%, 100%, and 125% of a base rate, NBR), and with four replications. As expected, corn grain yields increased with irrigation and N fertilizer. Mean corn grain yields for the three-year study ranged from 6.3 to 8.9 Mg/ha for the 0% IBR treatment, 9.4 to 10.5Mg/ha for the 75% IBR treatment, and 10.0 to 10.6 Mg/ha for the 150% IBR treatment. The mean corn grain yields in response to N applications ranged from 6.4 to 8.0 Mg/ha for the 50% NBR treatment, 8.6 to 9.4 Mg/ha for the 75% NBR treatment, 9.1 to 10.9 Mg/ha for the 100% NBR treatment, and 8.8 to 11.7 for the 125% NBR treatment. However, the nature of the response varied among the three years, mainly because of differences in rainfall and rainfall distribution during the growing season. Also, during the first year, there was less response to N fertilizer (7.9 to 9.1 Mg/ha) possibly because of residual soil N from antecedent soybean crop. A regression analysis indicated that the slopes of the corn yield response to increased N fertilizer application were low for both irrigated and rainfed treatments in 1999. In both 2000 and 2001, the slopes were greater for the corn yield response to increased N fertilizer. In 2000, the irrigated treatments had a greater slope of the yield response for additional N fertilizer than did the rainfed treatments. Using an orthogonal contrast analysis, the overall yield response for the combined irrigation treatments to N fertilizer was quadratic in 1999 and 2000, and linear in 2001. These quadratic yield responses indicated that, for these conditions, a potential upper limit on production for the applied N-fertilizer and water (rainfall and irrigation) was approached. For the rainfed treatment, yield response to N fertilizer was linear in all three years. These results provide useful information that should be helpful in developing management strategies and decision support systems for profitable management of both water and N fertilizer on spatially-variable soils in the southeastern Coastal Plain while conserving natural resources and protecting the environment.

There currently are no data on using reduced tillage for flax (Linum usitatissimum L.) production when double-cropped after cotton (Gossypium hirsutum L.) in the southeastern USA. This study evaluated how tillage and subsoiling influenced double-cropped flax and cotton productivity and quality under conditions in the southeastern USA. An irrigated study on a loamy sand soil (Eunola loamy sand) was conducted beginning in spring 2001 through spring 2003. Treatments evaluated in both crops were subsoiling (subsoiled to 30-cm or none) and tillage (chisel plow to 20-cm plus disking, disking only, and no tillage). Standard fiber test methods were used to evaluate treatment effects on fiber properties. Subsoiling increased the cotton and flax yield. Cotton yields were not influenced by tillage treatment while flax dry plant matter yields were greater for chisel and disk treatments compared with the no-tillage treatments. Fiber properties, cotton micronaire, fiber length, and fiber length uniformity, and flax fiber strength were impacted by tillage. Our results indicate that for this double-crop system, no tillage with subsoiling is a viable practice for cotton but further research is needed to improve flax productivity with this management practice.

Judging from archaeological evidence, irrigation has been practiced for at least eight millennia, starting in the Nile, followed by the Tigris and Euphrates in Mesopotamia, the Yellow River in China, and the Indus River in India (Hoffman et al., 1990). During this time, the experience and skill of humankind has been accumulated, improved with an eye toward future needs, and yet sometimes still lost to history. Therefore, capturing the state of the art of irrigation is clearly worthwhile. On the other hand, predicting the future is far less so clearly worthwhile. We recognize that our foresight may well in time be proven dim. Bearing in mind the context of 80 centuries, however, we attempt to describe new and predict future trends.

A loamy sand Acrisol (Aquic Hapludult) that had been microirrigated for 6 years became so severely compacted that it had root limiting values of soil cone index in the Ap horizon and a genetic hardpan below it. Deep and surface tillage systems were evaluated for their ability to alleviate compaction. Deep tillage included subsoiling or none. Both deep tillage treatments were also surface tilled by disking, chiseling, or not tilling. Subsoiling was located in row or between rows to avoid microirrigation tubes (laterals) that were buried under every other mid row or every row. Cotton (Gossypium hirsutum) was planted in 0.96-m wide rows. Cotton yield was improved by irrigation from 485 to 1022 kg ha � 1 because both 2001 and 2002 were dry years. Tillage loosened the soil by an average of 0.5–1.3 MPa; but compacted zones remained outside tilled areas. Subsoiling improved yield by 131 kg ha � 1 when performed in row where laterals were placed in the mid rows; but subsoiling did not improve yield when it was performed in mid rows. For subsurface irrigation management in these soils, the treatment with laterals buried under every other mid row was able to accommodate in-row subsoiling which improved yield; and this treatment was just as productive as and had been shown to be less expensive to install than burying laterals under every row. Published by Elsevier B.V.

Site-specific irrigation is defined as delivering different prescribed depths of water to specific areas in irrigated fields. Since the 1990s, site-specific irrigation research has been expanded to include the delivery of water and nutrients to specific field areas based on soil type, soil moisture status, crop needs, and other user-defined objectives. A site-specific center pivot irrigation system was designed and installed in a field with highly variable soils of the U.S. eastern coastal plain. The system consisted of 13 segments along the 140-m length of the three-tower center pivot with three delivery manifolds in each segment. The system was designed to apply approximately 12.5 mm of water in any selected segment when operated at 50% travel velocity. Quantifying water application depth and uniformity from the site-specific irrigation system is essential to documenting the system’s performance and interpreting experimental results. We developed a measurement system to evaluate the water delivery rates of the irrigation system. We compared the measured water delivery from each segment of the site-specific irrigation system to the design parameters. We found that the irrigation system was delivering water to the control areas at rates approximately as it was designed. A total of 77 segment and manifold combinations were tested. Of these 77 combinations, we found that 7 had flow rates greater than 10% different from the design flows. The manifolds with the lower flow rates typically were more likely to differ significantly from their design values. This was most likely related to potential clogging of the low flow nozzles that have smaller orifices. When the manifolds were used in combination, they compensated for each other and produced application depths near the design depths.

This paper evaluates the economic feasibility of variable rate applications (VRA) of irrigation water in corn production. The data were obtained from an experiment conducted at the site-specific center pivot irrigation facility at Florence, SC, INTERNAT, during the 1999-2001 seasons. The field was divided into 396 plots and a water production function was estimated for each plot to determine the optimal amount of irrigation water for each plot. Net returns from VRA applications were compared with uniform applications. The results indicate that the VRA applications yielded larger net returns than the uniform applications. However, the VRT applications require additional equipment and control. The benefits of reduced irrigation water costs plus the value of increased yields must be greater than the additional costs associated with the VRT application. Because the VRT system used in this experiment was built for experimental research purpose, the costs were much higher than those that would have bee...

N-fertilizer and irrigation water are major inputs to corn production and efficient use of these inputs is essential for profit maximization and resource conservation. To use these inputs efficiently, knowledge about plant responses to N-fertilizer and irrigation water, or production functions, is essential. Corn production functions were estimated using the data from experimental plots in Florence, South Carolina, U.S.A., from 1999 through 2001. There were three irrigation treatments and four N-fertilizer regimes. Several forms of production functions were fitted to the data and the quadratic form of the production function was found to have the best fit for the data. The estimated production functions were then used to determine the optimal levels of water and N-fertilizer applications under both yield-maximizing and profit-maximizing strategies. Results indicate that the yield-maximizing strategy called for more water and N-fertilizer and yielded smaller net returns than the profit-maximizing ...

Water is a precious resource and is used in many competing industries. To use water efficiently in crop production, knowledge about crop responses to irrigation water, or the production function, is essential. In this paper, we estimated six production functions, two N-fertilizer treatments for each year in 1999, 2000, and 2001, for corn production using the data from experimental plots in Florence, South Carolina, USA. Optimal levels of irrigation and gross margins under profit-maximizing and yield-maximizing strategies were computed. The results indicate that at the current prices of corn and water in South Carolina, the profit-maximizing strategy conserved more irrigation water and produced larger gross margins than the yield-maximizing strategy. The differences in optimal levels of irrigation water and gross margins between the two strategies became even more significant when the relative water/corn price ratios increased. To find out how demand for irrigation water responds to changes in wat...

A better understanding of how drought stress affects soybean [Glycine max (L.) Merr.] seed-yield determination would aid in the development of improved cultivars for the southeastern Coastal Plain and better production systems aimed at ameliorating the effects of drought stress. The objective of this field study was to examine the effects of drought stress on both soybean branch vegetative growth and the distribution of seed yield and yield components between the main stem and branches. Soybean was grown on an Eunola loamy sand in 1998 and 1999 with three levels of drought-stress treatment: (i) irrigation and no deep tillage, (ii) deep tillage but no irrigation, and (iii) no deep tillage or irrigation. Total seed yield, branch seed yield, and the percentage of total seed yield on the branches were highest with irrigation, followed by the in-row subsoiled/no deep tillage treatment and the no irrigation/no deep tillage treatment. Drought-stress treatment had no effect on mainstem seed yield. Branch seed number per square meter was highly correlated with branch seed yield (r = 0.994; P < 0.0001) and total seed yield (r = 0.989; P < 0.01) over both years and all levels of drought-stress treatment. A close relationship was found between branch seed number per square meter and branch dry weight at harvest maturity (r = 0.963; P < 0.05), final branch length per square meter (r = 0.994; P < 0.05), and final branch number per square meter (r = 0.995; P < 0.05). Most branch growth occurred between initial flowering and the beginning of seed fill. Less association was found between individual seed weight and seed yield from the mainstem or branch fractions. These data indicate that drought stress occurring between initial flowering and seed fill decreases total seed yield primarily by reducing branch vegetative growth, which reduces branch seed number and branch seed yield.

During the past decade, there has been increasing interest in applying water and chemicals to crops based on need or yield potential rather than applying uniformly to the entire field. While ground-driven variable-rate chemical application equipment is now being used, most irrigation systems continue to apply nominally uniform water depths. Our objective was to make variable-rate irrigation applications possible by developing a digitally controlled metering device. The device consists of a reservoir that is alternately filled and emptied at a rate determined by a digital pulse from an external source and requires pressurized sources of water and air. The flow rate can be altered by changing the cycle duration and frequency, by changing air and water pressure, or by exchanging the reservoir with one of different volume. Tests with prototypes indicate reproducible flow rates for a range of operating pressures and discharge cycle durations. Various sprinklers or nozzles may be attached to the outlet if specific distribution patterns are desired. Additionally, the metering device can be used in a wide variety of applications with a variety of fluids or gases for variable-rate flow or injection of a fluid into either another fluid or gas.

Subsurface drip irrigation offers many advantages for management of water and nutrients, but its effectiveness may be limited by weather or soil conditions. Solving soil problems, such as compaction, in subsurface drip irrigation systems is understandably difficult using deep tillage. We hypothesized that the need for deep tillage in conservation tillage systems may be reduced if the compacted soil layers are kept moist enough for root growth. A twoyear experiment that included wheat, soybean, and cotton under no-tillage culture was conducted with subsurface drip irrigation. The irrigation system had been used for five years before this experiment and provided two irrigation drip line spacings (1 m and 2 m) and three irrigation amounts (6, 9, and 12 mm/application). Irrigated soybean yields were greater than rainfed in one of the two years. No differences in yield occurred among irrigation drip line spacing or irrigation amounts. Also, neither cotton nor wheat yields were increased by irrigation. Observations during the growing seasons, cotton root observations after harvest, and soil strength measurements during the spring indicate that considerable soil compaction occurred at very shallow soil depths (< 5 cm) and restricted root growth. This compaction probably limited the efficacy of subsurface drip irrigation, which was located at the 30-cm depth. Based on these results, it appears that strategies must be developed to reduce soil strength to obtain optimum no-tillage crop production with subsurface drip irrigation on these soils.

Excessive N application to cotton (Gossypium hirsutum L.) is an unnecessary cost and a potential cause of elevated groundwater N. The objectives of this study were to determine if seed yields or excess N were affected by timing of N application via buried microirrigation tubing, tubing spacing, or peanut (Arachis hypogaea L.) rotation. The experimental design was a randomized complete block in split-plot arrangement with four replications. The main plots (continuous cotton and peanut-cotton rotation) were planted with cotton cultivar PD 3 in May of 1991 through 1994 on an Eunola loamy sand (fine-loamy, siliceous, thermic Aquic Hapludult). Water and N were applied through microirrigation tubing that was buried 0.30 m directly under each row (IR) or under alternate row middles (AM). Sidedress-N was applied in one 112-kg ha -1 application (STD); five, 22-kg ha -1 increments (INC); or 11- to 22-kg ha -1 increments when required by GOSSYM/COMAX (GC) [a cotton growth model/expert system]. Rotation did not significantly affect any of the measured parameters. Cotton managed with the IR-STD treatment had the highest seed yield, 2.02 Mg ha -1 yr -1 . The GC management did not improve seed yield, but it did reduce excess N (fertilizer N - seed N) to

Spatial yields since 1985 in a corn-wheat-soybean rotation at Florence, S.C., show little correlation of yield data with expected yields for soil map units. Research suggests that spatial yield variability for the southeastern Coastal Plain may be caused primarily by water relations. This causes difficulties in scheduling irrigation for conventional center pivot irrigation systems, which are not capable of applying variable depths of water to small areas of variation within the total system. Thus, the objectives of this work were to design and construct a site-specific center pivot irrigation system that could independently apply variable rates of water and chemicals to 100-m2 areas within the irrigation system. A commercial center pivot system was modified by adding three 9.1-m manifolds in each of 13 segments along the truss. Nozzles were spaced 1.5 m apart along each manifold, and both manifolds and nozzles were sized to provide 1x, 2x, and 4x nominal application rate at a given tower speed. All combinations of the three manifolds provided up to 7x nominal depth, which was 12.7 mm, in 1.8-mm increments when the outer tower traveled at 50% of full speed. A programmable, computer-controlled management system was installed near the pivot on the moving portion of the center pivot system. This controller obtained the position from the center pivot controller via a radio frequency modem and switched on the appropriate valves to obtain the application rate for a specific area. During 1995 and 1996, the system applied water and N fertilizer in a fixed-boundary field experiment. Measurements and observations of water and N application uniformities were acceptable; however, more extensive evaluation will be required before definitive conclusions can be reached regarding N application. Surface temperatures measured with an integral infrared thermometer system produced encouraging results that may be useful in management of water and nutrients. Using experience gained with this system, a second commercial center pivot system is being modified for site-specific water, nutrient, and pesticide management on a field with soil variation (irregular boundaries) typical of the Coastal Plain.

A comprehensive review of published information on subsurface drip irrigation was performed to determine the state of the art on the subject. Subsurface drip irrigation has been a part of drip irrigation development in the USA since its beginning about 1960, but interest has escalated since the early 1980s. Yield response for over 30 crops indicated that crop yield for subsurface drip was greater than or equal to that for other irrigation methods, including surface drip, and required less water in most cases. Lateral depths ranged from 0.02 to 0.70 m and lateral spacings ranged from 0.25 to 5.0 m. Several irrigation scheduling techniques, management strategies, crop water requirements, and water use efficiencies were discussed. Injection of nutrients, pesticides, and other chemicals to modify water and soil conditions is an important component of subsurface drip irrigation. Some mathematical models that simulate water movement in subsurface drip systems were included. Uniformity measurements and methods, a limited assessment of root intrusion into emitters, and estimates of overall system longevity were also discussed. Sufficient information exists to provide general guidance with regard to design, installation, and management of subsurface drip irrigation systems. A significant body of information is available to assist in determining relative advantages and disadvantages of this technology in comparison with other irrigation types. Subsurface drip provides a more efficient delivery system if water and nutrient applications are managed properly. Waste water application, especially for turf and landscape plants, offers great potential. Profitability and economic aspects have not been determined conclusively and will depend greatly on local conditions and constraints, especially availability and cost of water.

Soil penetration resistance (cone index) varies with water content. The field variation of water content could mask treatment differences. The correction of cone index data to a single water content would help prevent this. We used equations from TableCurve™ software and from the literature to correct cone indices for differences in soil water contents. Data were taken from two field experiments where cotton (Gossypium hirsutum L.) was grown using conventional and conservation tillage without irrigation, and beans (Phaseolus vulgaris L.) were grown using conventional tillage with microirrigation. Boundary conditions based on hard, dry and soft, wet soils were imposed on the equations. Equations fit the data with coefficients of determination ranging from 0.55 to 0.92 and error mean squares from 1.37 to 6.35. After correction, cone index dependence on water content was reduced. A single-equation correction did not always fit the data across all treatments. Separate corrections, based on treatment, might be required. When corrections required multiple equations, differences may be real or may be a manifestation of the correction differences. In this case, the correction may not be feasible (unless some future work can coordinate different equations and assure a uniform correction).

The cost of drip irrigation can be reduced by using both wider lateral spacings and the same laterals for multiple years, as with subsurface placement. Multiple, low-rate fertilizer and water applications may reduce N fertilizer needs by improving efficiency and limiting the potential for leaching. The combination of these technologies may make drip irrigation of cotton profitable. Four years of continuous cotton and two years of cotton rotated with peanut were evaluated. Two subsurface drip irrigation lateral spacings (every row, 1 m, and alternate furrow, 2 m) and three sidedress-nitrogen methods (STD, single application of 112 kg/ha; INC, 112 kg/ha in five equal applications; and GOS, applications determined by GOSSYM/COMAX) were evaluated for cotton during 1991-1994. Two of the sidedressnitrogen methods (STD and GOS) were evaluated for a rainfall-only treatment. Lint yields did not differ between the lateral spacings in any year. Yields for irrigated treatments were 16 and 65% greater than rainfall-only yields in 1992 and 1993, respectively. The GOSSYM/COMAX-managed nitrogen treatment received 30% less nitrogen fertilizer than other treatments, but had similar lint yield. Several fiber physical properties were affected by irrigation and nitrogen, but these effects were small and inconsistent. For continuous cotton, or cotton rotated with peanut, the wider lateral spacing is preferred to the every-row spacing because of its lower initial cost (about 30%). The combination of lower system cost, longer system life, and lower N-fertilizer requirements could make subsurface drip irrigation of cotton profitable for southeastern Coastal Plain soils, and reduce the potential for ground water contamination.

Three drip irrigation systems were installed in 1984, two with laterals on the soil surface and one with laterals about 0.30 m below the soil surface. These systems were used to apply irrigation water and nutrients to several experiments from 1985 to 1992. Emitter plugging, system uniformity, and overall performance were evaluated for both surface and subsurface systems using several methods, and the results were compared to those obtained for unused tubing that had been saved from the original lot. Emitter uniformity values calculated for the unused laterals by the traditional and ASAE EP458 methods were similar, but differences between parameter values calculated by the two methods were greater for the used laterals, especially in the subsurface system. All uniformity values were lower for the subsurface system, primarily because of plugged emitters. Uniformity values calculated by the EP458 method (randomly selected emitters) indicate lower emitter uniformity for the used laterals in the subsurface system, but these values were not as low as those calculated using all emitters on three laterals for that system. These values indicate that the EP458 method may not always reflect true system uniformity, probably because of the small sample size and existence of completely plugged emitters. Correction of emitter flow rates for temporal pressure variation among test times improved uniformity parameter values slightly. Uniformity values predicted by design/evaluation models were similar for both surface and subsurface systems, and generally indicate better system uniformity than values calculated from emitter flow measurements. The models were unable to predict reliable uniformity values for systems because of their inability to handle emitter plugging. Based on these results, it appears that both traditional and ASAE EP458 methods can be used to evaluate drip irrigation systems, but the EP458 method generally indicates lower uniformity and should be used carefully for systems where completely plugged emitters may exist. When emitter plugging occurs, the accuracy of predictions by either method will depend primarily upon the number of emitters measured and the extent of plugging. Entry of soil particles into this eight-year-old subsurface system during construction and/or repair operations probably caused the observed emitter plugging, which emphasizes the need for exercising great care in installation and maintenance of subsurface systems if a long system life (10-15 years) is expected.

A multiple-segment water application system was developed and attached to a commercial center pivot irrigation system to provide variable application depths within each segment at a given speed. Each segment was 9.15 m (30 ft) long and consisted of three parallel manifolds sized to provide 1x, 2x, and 4x, where x is a minimum application depth. The three manifolds could be operated individually or in various combinations to provide eight application rates (0-7x) at any given tower velocity. Water application depth varied from 0 to 12.4 mm (0 to 0.5 in.) when the center pivot was moving at 50% of full speed. Water was delivered via industrial, full-cone, and wide angle spray nozzles that were selected to provide the desired range of application depths for the entire length of the pivot. The irrigated areas for each angular increment were small at the pivot end of the system and required nozzles with small discharge rates while at the distal end the areas were larger required nozzles with larger discharge rates. Agricultural chemicals, especially nutrients, that can be injected into the irrigation water may also be applied at the same range of rates provided the chemical concentration is constant.

An experiment was conducted in Southern Louisiana during 1980 through 1990 to determine soil and crop response to subsurface drainage. Three subsurface drain spacings, 14, 28, and 42 m, were tested on Jeanerette silty clay loam soil. The 14 and 28 m spacings were most effective in controlling the water table: average annual SEW30 values were 46 and 122 cm-d, respectively. Average annual SEW30 value for the 42 m spacing was 242 cm-d while that from the nondrained check was 642 cm-d. Sugarcane responded favorably to subsurface drainage. Average annual sugar yields were 6041 kg/ha from the 14 m spacing, 6029 kg/ha from the 28 m spacing, 5788 kg/ha from the 42 m spacing, and 4990 kg/ha from the check. Yields among the three drained treatments were not significantly different, but yields from the drained treatments were significantly greater than those from the nondrained check. The value of the average sugar yield increases from both the 28 m and the 42 m spacings more than justified the cost of installing subsurface drainage systems. The drainage costs included 10% interest and a 10-year amortization period. Since there was no statistically significant crop yield advantage to subsurface drains spaced closer than 42 m, the drain spacing recommended for draining Jeanerette silty clay loam soil in Louisiana is 42 m.

Excessively wet and dry soil conditions can occur during the same year in the southeastern Coastal Plain of the United States. Water management systems that provide both subsurface drainage during wet soil conditions and irrigation during dry soil conditions are desired. Several water table management alternatives, possibly with surface irrigation such as microirrigation, could satisfy these needs. Three water table management (WTM) systems and microirrigation were evaluated for three cotton cultivars on a southeastern Coastal Plain soil during 1987-1989. The WTM systems included controlled drainage-subirrigation (CDSI), controlled drainage (CD), and subsurface drainage (SSD). All WTM systems had both surface microirrigation and rainfed treatments. Cotton cultivars were Coker 315, DPL 50, and DPL 90. Seasonal rainfall, subirrigation, and microirrigation amounts varied considerably during the three-year period. Water requirements for subirrigation in the CDSI system were high (1477 to 2841 mm), but neither microirrigation nor subirrigation water requirements were closely related to seasonal rainfall amounts. Cotton lint yields among WTM systems were significantly different in two of three years; yields for the CDSI system were lowest (836 and 766 kg/ha) and yields for CD and SSD were highest (1022 and 942 kg/ha, respectively). Wetter-than-optimum soil conditions in all irrigated treatments, especially in combination with the CDSI system, probably caused the reduced yield. Microirrigation produced significantly greater lint yields than the rainfed treatments in the first two years of the study (1127 and 1116 kg/ha versus 492 and 801 kg/ha), but not in the last year (872 versus 874 kg/ha) when seasonal rainfall was least of the three years but was better distributed. There were significant yield differences among cotton cultivars in two years, but no cultivar consistently produced the greatest or least yield. Cotton yield increases obtained with these WTM system-microirrigation combinations suggest the need to control the water table closer to the soil surface in southeastern Coastal Plain soils when surface irrigation is not used. The CDSI could provide a profitable management alternative if a water table fluctuates near the soil surface much of the time, especially during the growing season. Where subsurface drainage is needed part of the year, it may be more profitable to use CD or SSD systems with surface irrigation, especially when maintaining the water table near the soil surface in CDSI systems requires a large water volume. However, the combined cost of the subsurface drainage and microirrigation systems would be very high and might not be profitable for crops such as cotton.

Restricted root growth caused by subsurface hardpans and low water holding capacity reduces crop yields in many United States southeastern Coastal Plain soils. With intensive irrigation it is possible to obtain suitable yields without deep tillage. The objective of this study was to find differences of root growth and cone indices between surface and subsurface applied sources of irrigation water. We measured root growth and cone index in intensively managed irrigation plots of green beans ( Phaseolus vulgaris L.) in 1988 and 1989. Microirrigation tubes were placed on the surface or in the subsurface — buried at a depth of approximately 0.25 m — and irrigated either continuously or with intermittent pulses of water. Mean profile cone indices for the surface tube placement were significantly lower than for the subsurface tube placement. Mean profile cone indices for the continuous irrigation treatment were significant lower than for the intermittent irrigation treatment. However, no one treatment significantly reduced the cone indices within the hardpan. Total root count was significantly greater for the subsurface tube placement with increased root growth below the 0.1-m depth. There was a high density of roots next to the subsurface tube that would have been effective in uptake of water from the microirrigation tube. However, yield was significantly greater for the surface tube placement. For all treatments, the largest concentration of root growth occurred in the top 0.2 m of the soil within the row. We expected this for the surface irrigation treatment. However, we also measured this for the subsurface treatment, probably because of high rainfall and upwelling of water from the subsurface micro-irrigation tube.

Installation of microirrigation tubing below the tillage zone and/or at wide spacings could make microirrigation more profitable for supplemental irrigation of vegetable crops in humid areas such as the southeastern U.S. coastal plain. Two surface (surface 1 and surface 2, either one or two tubes/bed) and one subsurface (Subsurface 2, two tubes below each bed) microirrigation treatments and two application frequencies, high (three times per day) and low (one time per day), were evaluated for cowpea, green bean, squash, and muskmelon production in the spring seasons and for broccoli in the fall seasons. The same irrigation equipment was used in both years and for three years prior to the experiment. There were few yield differences among irrigation treatments, both for tubing placement and irrigation frequency. There was no yield reduction for the surface 1 treatment, although it received only half the irrigation volume as the other treatments. Therefore, for the irrigation systems evaluated, the surface 1 system would be more profitable for vegetable production in the southeastern coastal plain. All yields were as high or higher than industry yields, except for broccoli, which was slightly lower. These results demonstrate the feasibility of multicropping vegetables with the same irrigation system. The satisfactory performance of the microirrigation tubing after five years of use indicates a high probability that the longevity of this system may be sufficient to make it profitable for use with lower-valued crops and other vegetable crops.

Three irrigation scheduling methods and two microirrigation tube placements were evaluated on three cotton (Gossypium hirsutum L.) cultivars for three years on a southeastern Coastal Plain soil. Irrigation scheduling methods included two computer models, GOSSYM/COMAX and PRISM, and a method using tensiometers. Microirrigation tubing was placed on the soil surface, either adjacent to every row or in alternate furrows. Growing-season rainfall amounts ranged from 313 mm in 1990 to 544 mm in 1988. Rainfall distribution also varied widely within each year. In a similar manner, irrigation amount and frequency varied among scheduling methods and years, but no method consistently required the largest or smallest amount of irrigation. Cotton lint yields ranged from 850 to 1105 kg/ha over all years, but there were few significant differences among irrigation treatments within a year, even between the rainfall-only and irrigated treatments. Lint yields were significantly greater for the PD3 and DPL90 cultivars than for the Coker 315 cultivar during the three-year period, and the PD3 cultivar had a greater yield response to irrigation. The tensiometer-every row tube placement is the only irrigation treatment that produced cotton lint yields significantly higher than the rainfall-only treatment each year. The tensiometer scheduling method also produced significantly greater yields each year. Although yield differences occurred, they were relatively small. This fact, along with the inconsistent differences in the amount of irrigation water required, suggests that the preferred method for a particular application will probably depend more upon water or labor requirements, cost, or personal preference. Also, there was no difference in yield between the two tube placements. Because the alternate-furrow placement requires only half as much tubing, which will reduce installation costs by about 30%, it appears to be the preferred placement for this soil. Further research is needed to refine irrigation scheduling for cotton in this region.

Two tomato (Lycopersicon esculentum, Mill.) experiments were conducted for two years on a southeastern Coastal Plain soil that has a high, fluctuating water table. In one experiment, two methods for managing microirrigation were compared to a treatment that received only rainfall by measuring marketable fruit yields for spring and fall cropping seasons. Irrigation increased yields for both seasons in the second year because of low rainfall. Measurements among seven shallow wells on the site showed no consistent differences for either water table depth or gradient between adjacent wells. Two cultivars were evaluated in the second year, primarily because frost severely damaged the tomato plants about three weeks after transplanting. In the second experiment, two excessively irrigated treatments were evaluated in an effort to induce a "soft-fruit" storage and shipping problem experienced by many growers in this region. Although extremely large quantities of irrigation water were applied, these symptoms were not observed in this study. There were no differences in fruit yield between the two water management treatments in either spring or fall. Fruit quality measurements showed no significant differences. The 'Sunny' cultivar performed better than 'Walter' during the fall season for the extremely wet soil condition. A double-crop, microirrigation management system has higher input costs but provides increased profitability for fresh-market tomato production, particularly where markets are available for both spring and fall crops.

SOJKA R. E., SADLER E. J., CAMP C. R. and ARNOLD F. B. A comparison of pressure chamber, leafpress, and canopy iemperatureforfror species under humid conditions. ENVIRONMENTAL AND EXPERIMENTAL BOTANY 30, 75-83, 1990.—Numerous techniques are currently available for measurement of plant water status in field environments, including pressure chambers and indices based upon infrared-determined canopy temperatures. The Campbell-Brewster (J-14) leaf press has been promoted as a compact alternative to the pressure chamber for plant water potential determination. In-depth comparisons of the J-14 ('P J) with the pressure chamber ('P) or with canopy temperatures (T) and crop water stress index (CWSI) have been limited, and an evaluation of the technique in a humid environment was needed. All three J-14 end points [exudation from cut (T R) or uncut leaf edges (T N) or darkening of interveinal areas (T N)] were highly correlated among themselves for the four species studied. Correlations of J-14 end points with other stress indicators from unstable diurnal periods were poor. None of the water status indicators correlated well with leaf diffusive resistance. Our data showed a species-related reliability of the J-14. The J-14 produced r 2 values above 0.7 for soybean [Glycine max. (L.) Merr.] for all but comparisons with CWSI or T, minus air temperature (ST), and for corn (Zea mays L.) for '11„ only. The J-14 did not perform well for tomato (Lypersician esculentum Mill.) or rapeseed (Brassica napes L.), and is probably best regarded only as a relative indication of plant water status in the absence of calibration with other techniques. Failure of 'P„ or J-14 to correlate well with CWSI underscores difficulty with CWSI measurement under humid conditions.

When compared with other irrigation systems, subsurface drip irrigation (SDI) has advantages and disadvantages that should be carefully considered. There are many design and management similarities to surface drip irrigation (DI), but there are also some unique differences that affect uniformity, operation, and system longevity. Factors that affect SDI uniformity are emitter clogging, root intrusion, root pinching, mechanical and pest damage, soil overburden and compaction, soil hydraulic parameters, and, possibly, system age. A typical SDI system often requires additional components, compared to DI, such as flushlines, additional air/vacuum relief valves, and pressure gauges and a flowmeter for system monitoring. Emitter flowrate and spacing, and dripline diameter, wall thickness, spacing, and depth are all important design criteria for SDI systems. Flushing of SDI driplines is also a key design criterion, and some designers prefer to begin their design with the flushing system. SDI can potentially provide a more consistent soil water and nutrient environment for optimum crop growth, but there can also be challenges in some regions, such as crop establishment, salinity management, soil water redistribution, and application of some agrochemicals. The application of SDI for some of the lower-value grain and fiber crops has been increasing, and this trend is likely to continue.

Site selection for subsurface drip irrigation (SDI) in the humid region must be carefully considered to ensure optimum system performance and crop yield while minimizing unnecessary expenses. SDI has been shown to result in similar or higher crop yields on many crops while reducing water use. However, characteristics of the field, soil, crop, cropping system, water resource available, managerial and farm labor resources, economic factors, and industry support infrastructure affect decisions about the appropriateness of SDI in a given situation. These topics are discussed with emphasis on their effect on the humid regions of the United States.

Measurement of water stress and scheduling of irrigation are both enabled by non–contact infrared thermometers (IRTs). Technological advances have miniaturized IRTs and reduced power requirements so that inexpensive self–powered units are now commercially available. The objective of this work was to test a linear array of IRT sensors mounted on a center–pivot irrigation machine, and to use this IRT array to examine spatial variation in water stress of corn under four irrigation treatments imposed on a highly variable field with a center pivot equipped for site–specific irrigation and agrochemical application. An array of 26 IRTs was mounted on the pivot, which was run dry for a full circle on 7 days during the 1999 corn growing season. Procedures were developed to adjust for time lag during the 3.5–hr measurement period. Significant differences were obtained among the varying water treatments, as expected, but also among plots within the same soil map unit and among soil map unit means. Distinct spatial patterns, not necessarily related to the 1:1200–scale soil map, were observed. These results emphasize the necessity to consider soil water relations during the development of management recommendations for site–specific agriculture.

The maximum amount and rate of nutrient accumulation by irrigated corn (L.) must be known so that farmers do not waste money or pollute water resources by applying excessive amounts of fertilizer. Aerial whole plant samples were therefore collected from irrigated field experiments conducted on Norfolk (Typic Paleudults) loamy sand in 1980, 1981, and 1982, to determine seasonal dry matter, N, P, and K accumulations for corn yielding 10 Mg ha or more in the southeastern Coastal Plain. Rates of accumulation were derived by differentiating compound cubic polynomial equations that described seasonal accumulation patterns. Total dry matter accumulation averaged 23.1 and 24.9 Mg ha for two population treatments that averaged 7 ✕ l0 or 10 ✕ l0 plants ha. Aerial N, P, and K accumulation respectively averaged 228,58, and 258 kg ha in 1980; 264,37, and 372 kg ha in 1981; and 225,37, and 335 kg ha in 1982. Grain yields averaged 13.4, 11.7, and 10.9 Mg ha in 1980, 1981, and 1982, respectively. Lower P accumulations in 1981 and 1982 were the result of lower grain yields that were apparently caused by excessive K accumulation. Calculated peak dry matter, N, P, and K accumulation rates were 650, 10, 1.6, and 28 kg ha day in this study, compared to rates of 247,4.5,0.6, and 3.2 kg ha, respectively, in previous midwestern studies. Peak accumulation rates during both vegetative and reproductive growth stages emphasize that cultural, nutrient, and water management practices must be coordinated to provide a minimum stress production environment for high corn yield.

POOR rainfall distribution and soil physical conditions such as high soil strength and low water-holding capacity often limit production of crops such as corn (Zea mays L.) in the Southeastern Coastal Plain. To produce high and profitable corn yields in this region, proper water, nutrient, and cultural practices must be implemented. This study was conducted to determine whether different irrigation scheduling methods, row configurations, plant populations, or fertilization programs could improve energy or water efficiency or improve corn yields. Nonirrigated production was compared to irrigated production where irrigation was scheduled by two methods. In 1980 irrigation was initiated when soil-water tensions reached either 25 (TENS 25) or 50 kPa (TENS 50) in the 30- to 60-cm depth range. In 1981 and 1982, irrigation was initiated when soil-water tension in this depth range reached 25 kPa or when indicated by a computer-based water balance (CBWB). Irrigated treatments produced an overall average corn yield of 12.08 Mg/ha while the nonirrigated treatment produced an average yield of 6.70 Mg/ha. There were no significant differences in corn yield between scheduling methods, but, compared to nonirrigated treatments, irrigation increased yields 150, 161, and 8 percent in 1980, 1981, and 1982, respectively. The CBWB consistently overestimated available soil-water volume both years, particularly during pollination and early grain fill periods when evapotranspiration was high. Row configurations evaluated included single rows spaced 96 cm apart and twin rows spaced 30 cm apart on 96-cm centers. The twin-row configuration significantly increased corn grain yield each year by an average of 0.64 Mg/ha presumably because of reduced intrarow competition for water and increased light interception...

Grain deficits frequently occur in the Southeastern Atlantic Coastal Plain because erratic rainfall patterns and soil properties often limit corn (Zea mays L.) yields, however, harvesting corn for silage may enable farmers to produce a second grain crop during the same calendar year. Effects of row spacing, plant population, and fertilizer program on yield, quality, and mineral concentrations of corn silage grown with irrigation on Typic Paleudult soils were therefore investigated. Two plant population treatments which averaged 7.0 and 10.1 plants m‐2 were evaluated with two fertilizer programs that differed in N, N and K, and N, P, and K in 1980, 1981, and 1982, respectively. Each plant density by fertilizer combination was evaluated in single rows spaced 96 cm apart and in twin rows which approximately doubled the intrarow plant spacing. Plot size for the 2×2×2 factorial experiment ranged from 30 to 44 m2. Yield, quality, and mineral concentrations of corn silage grown in single rows spaced 96 ...

Lack of water because of erratic rainfall frequently limits corn (L.) production on Typic Paleudults in the Atlantic Coastal Plain. Traditionally, wide (96 cm) row spacing and low plant population have been used to prevent water stress, but recently landowners have begun to invest in irrigation systems. Changes in row spacing, plant population, or fertilization practices may be required to achieve maximum water-and nutrient-use efficiency with those systems. We evaluated plant population treatments averaging 7.0 and 10.1 plants m in single and twin rows on a Norfolk (fineloamy, siliceous, thermic Typic Paleudult) loamy sand during 1980, 1981, and 1982. Three water management [nonirrigated, irrigated using tensiometers (TENS) to measure soil-water potential for scheduling, and irrigated using a computer-based water balance (CBWB) for scheduling], and two fertilization programs were also evaluated in a four-factor split-plot design. Water management and plant population interacted significantly. Planting in twin rows increased grain yield an average of 0.64 Mg ha (l0 bu/A), but planting more than 7.1 plants m significantly increased grain yield only in 1980. Irrigation increased grain yield 150, 161, and 8% in 1980, 1981, and 1982, respectively, as a result of increased kernel weight and number of kernels per ear. Increasing total N, P, and K application beyond 200, 30, and 167 kg ha-’, respectively, did not significantly influence grain yield or yield components. Yield advantages of narrow rows can be obtained on Coastal Plain soils which require subsoiling by using a twin-row planting configuration. Irrigation can be scheduled using either tensiometers (soil-water potential) or a computerized water balance without significantly changing corn grain yield, nutrient accumulation, or yield components.

Two tomato cultivars were evaluated for two years on a southeastern Coastal Plain soil that had a high, fluctuating water table. Treatments included micro irrigation vs. no irrigation and two cultivars. No consistent water table differences in either water table depth or in gradient between adjacent wells were measured among seven wells on the site. Water table contribution to crop water requirement could not be measured in this experiment, but a relatively small amount of irrigation (78 and 82 mm) significantly increased tomato fruit size and yield in both years. The Tempo' cultivar produced larger fruit, a higher yield, and matured earlier than the 'FloraDade' cultivar, partly because of reduced incidence of disease. The *soft-fruit syndrome' storage problem experienced by many growers in this region was not observed in this study. The management system used has higher input costs but provides increased profitability for fresh-market tomato production.

CORN {Zea mays L.) and soybean {Glycine max (L.) Merr.) were grown on an 18-ha site near Florence, SC, under irrigated and nonirrigated conditions for a 3-year period (1979 to 1981). The three irrigation scheduling methods were, for corn, tensiometer (TENS), screen-covered evaporation pan (SPE), and computer-based water balance (CBWB); and, for soybean, TENS, SPE, 70% of screen-covered pan evaporation (0.7 SPE) in 1979 and 1980, and CBWB in 1981. A treatment that received only rainfall was included for both corn and soybean each year. Rainfall was near normal in 1979, below normal in 1981, and much below normal in 1980. Yields for irrigated treatments were higher than for nonirrigated treatments each year for corn, but yields for only some of the irrigated treatments were higher for soybean. There were generally no significant differences in mean corn and soybean yields among the three irrigation scheduling treatments. There were no consistent differences in mean volume of irrigation water required by the three scheduling methods for all 3 years, although, for soybean, SPE tended to require the most irrigation water and TENS tended to require the least irrigation water. Because no significant differences in water requirement or yield were found for the three scheduling methods, the choice among them is essentially a matter of personal preference until refinements are made in one or all of the methods. The CBWB method does offer the advantage of predicting irrigation requirements up to 5 days ahead, if weather forecasts are available.

Micro irrigation offers advantages in water and energy conservation, but cost of annual replacement of many components makes it unprofitable for most agronomic crops. Alternative tubing placements could improve profitability. An experiment was conducted for a three-year period (1985-87) to evaluate three micro-irrigation lateral placements and two irrigation application modes for corn in a coarse-textured southeastern Coastal Plain soil. Tubing placements were surface in-row (SIR), subsurface in-row (SSIR), and surface alternate middle (SAM). Irrigation application modes were continuous and pulsed. There were no differences in corn grain yield except during moderate-to-severe drought. Yields were significantly lower for the SAM treatments in 1986 and for the SAM-pulsed application mode treatment in 1987. Small differences in irrigation water were required among the three tubing-placement treatments. The SSIR treatment required the least amount of irrigation water each year. There was no evidence of emitter plugging on any treatment. The systems, still in use, will be evaluated for longevity; profitability can then be estimated. Based on these results, all of these placements of micro-irrigation tubing can produce acceptable corn yields in the southeastern Coastal Plain.

Amodel for predicting evaporation and temperature changes in water drops traveling through air was developed and evaluated with laboratory data. The model uses combined sensible heat transfer and diffusion theory in an energy balance to simultaneously calculate evaporation as droplet temperature approaches wet bulb temperature of the air. Predicted droplet temperatures agreed closely with measured temperatures. The evaporation portion of the model was evaluated by measuring loss of water over longer time periods after the droplet reached wet bulb temperature. A volumetric method using microliter syringes was used to measure evaporation loss from 0.5 to 2 mm diameter drops. Model predictions generally agreed with measured rates.

Crop water use data were extracted from literature data originating in the southeastern USA. Data were catalogued according to location, method of measurement, crop, time, duration of study, form of data, main treatments and concurrent data published. 101 unique crop-experiment citations were located. The following locations, in four states, accounted for 56 of these: Pontiac, SC; Thorsby, AL; Ft. Lauderdale and Belle Glade, FL; Raleigh and Waynesville, NC. Soil profile methods were used in 39; lysimeters were used in 44. The soil profile method of determining water use has been criticized for susceptibility to errors under high rainfall conditions common to the southeastern USA. Experimental methods were not always completely described, so limitations of the data were not always clear. A few citations included discussions of the limitations; most common was lack of fetch or conditions non-representative of field crops. From the review, it can be concluded that a conclusive study is lacking in the physiographic area. It is also considered that insufficient data exist for a conclusive test of transferability of western irrigation management technology into the more humid Southeast.

Full‐season determinate soybean [Glycine max (L.) Merrill] was grown in the field in a humid climate for three seasons (1979–81). The objective was to examine variability in several methods of determining basic relationships between soil and plant water status in a range of canopy configurations and to examine treatment effects on soil‐nutrient extraction. In each year, two cultivars, “Davis” (group VI) and “Coker 338” (group VIII) were planted in four row spacings. In 1980 and 1981 the experiment was expanded and split for irrigation and row orientation (N—S or E‐W). Post‐harvest soil samples were collected and analyzed to determine if irrigation, row spacing, or cultivar influenced K, Ca, and Mg extraction patterns. During the growing seasons, parallel leaf diffusive resistance (Rs) was poorly correlated with xylem pressure potential (ψx), canopy s x temperature (Tc), canopy minus air temperature (?T), leaf vapor pressure deficit (LVPD), and atmospheric vapor pressure deficit (VPD) in single fa...

A field study was conducted on an alluvial soil in Louisiana to determine the yield response of sugarcane to various subsurface drainage treatments that included three drain spacings (6.1, 12.2, and 24.4 m) and two drain depths (0.9 and 1.4 m). Annual rainfall was above the long-term mean during one year (1975) of the three-year study and was much lower than mean annual rainfall during the other two years (1974, 1976). All subsurface drainage systems adequately controlled the water table. Sugarcane and sugar yields for the subsurface drained treatments were significantly higher than yields for the undrained treatment during the wet year (1975) when the water table in the undrained treatment was very high during much of the year. The lower yield for the undrained treatment during the wet year was due primarily to lower plant population. Although yield increases were obtained for only one year, the magnitude of the increase for that year was large enough to defray a significant portion of the system installation cost

Field experiments were conducted to evaluate N and K fertilization rates, fertilizer placement, and water management practices for fresh‐market tomato (Lycopersicon esculentum Mill.) production in the Southeastern Atlantic Coastal Plain. Plant nutrient status, fruit yield, and fruit firmness after 12. to 15 days of storage at 20C were evaluated. Nitrogen rates of 130 or 200 kg/ha significantly increased yield of extra‐large and large fruit compared to the 67 kg/ha N rate. There was no significant difference in yield response among K rates of 46, 140, or 280 kg/ha. Marketable fruit yields for banded or broadcast placement of fertilizers beneath the black polyethylene mulch were not significantly different. Trickle irrigation did not cause extensive nutrient leaching or induce a “soft‐fruit”; storage syndrome. The ‘Tempo’ cultivar yielded significantly more extra‐large fruit with or without irrigation. However, after 12 to 15 days at 20C, internal firmness of physiologically similar fruit was lower...

Irrigation water costs are becoming of greater concern as groundwater supplies decrease and irrigation demands increase. This paper compares water storage costs for a stream water level control system (SWLC), which provides underground storage, with storage costs for impoundments and excavated ponds. A Fabridam, an automatic, water-inflatable dam was used to control the stream water level for a distance of more than 3 000 m (9800 ft) upstream. Underground storage volume was calculated from data collected during the driest year (1983) of a four-year study. A least-squares regression line through measured water volume values was determined and extrapolated to the lowest expected stream elevation. From this relationship, it was estimated that a water volume of 900 000 m3 (730 acre-ft) could be pumped frm the creek for irrigation with the Fabridam in place. This storage volume was used to determine the size, number and cost of impoundments and excavated ponds required to provide equivalent storage. Annual costs of irrigation water storages are $0,039, $0,051, and $0,121 per m3 ($48, $63 and $149/acre-ft), respectively, for SWLC, impoundments and excavated ponds. The lower-cost SWLC method could be used on an estimated 5 million hectares (12.4 million ac) of land in the southeastern Coastal Plain.

CORN {Zea mays L.) and soybean [Glycine max (L.) Merr.] were grown on an 18-ha site of Coastal Plain soils under nonirrigated and irrigated conditions for the three-year period, 1979-81. The five tillage treatments were double disking and minimum tillage, both with and without in-row subsoiling at planting; and disking with uniform chisel plowing. Rainfall during the growing season was near normal in 1979, below normal in 1981, and much below normal in 1980. There were significant yield differences due to tillage and irrigation for both corn and soybean. Corn yield increases due to deep tillage were greater in magnitude and were more consistent than those for soybean. Minimum tillage without subsoiling produced the lowest yields for both corn and soybean; however, this treatment had the poorest stand and the most severe weed competition of all treatments. Deep tillage and irrigation produced additive yield increases for corn, but not for soybean, indicating the possible need to use both management practices for corn in some soil conditions. Irrigation increased yields for both corn and soybean across all tillage treatments with mean yield increases of 3.37 t/ha (86%) and 0.73 t/ha (51%) for corn and soybean, respectively. The choice of management practices will depend upon their cost relative to their respective yield increase potential.