Carl R. Camp

Correction of cone index for soil water content differences in a coastal plain soil

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).

13. Subsurface drip irrigation

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.

Economic Feasibility Study of Variable Irrigation of Corn Production in Southeast Coastal Plain

ABSTRACT 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 been used for commercial growers. Even for the commercial system, the additional costs of VRT are more than the benefits of using VRT. Thus, at present, the VRT application of irrigation water is not profitable compared to uniform applications for South Carolina. However, the costs of these equipment and controls are declining over time. Furthermore, the costs would be much smaller when VRT is widely adopted by producers and these equipment and controls are mass-produced.

Optimal Levels of Irrigation in Corn Production in the Southeast Coastal Plain

ABSTRACT 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 water prices, demand functions for water were derived and demand elasticities of water were computed. At the current prices of water and corn, the demand elasticities were inelastic, which means that irrigation is not very responsive to changes in the price of water. As the price of water increased, demand for irrigation became more responsive to changes in water prices.

Site Selection for Subsurface Drip Irrigation Systems in the Humid Region

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.

Effect of Tillage on Double-cropped Flax/Cotton Production and Fiber Properties

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.

Efficient Allocations of Irrigation Water and Nitrogen Fertilizer in Corn Production

ABSTRACT 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 strategy. In 1999, for example, under the current average prices of corn, water, and N-fertilizer, the yield-maximizing strategy required 667 ha-mm of water and 224 kg of N-fertilizer to produce 10.4 Mg/ha of corn and

Cone index and root growth in surface and subsurface microirrigated hardpan soil

5.42 of net returns; whereas the profit-maximizing strategy required only 556 ha-mm of water and 174 kg of N-fertilizer to produce 9.87 Mg of corn and

Drought-Stress Effects on Branch and Mainstem Seed Yield and Yield Components of Determinate Soybean

57.38 of net returns. The least-cost combinations of water and N-fertilizer application levels for a given output were also determined. The results provide useful information to farmers to make N-fertilizer and irrigation decisions for profit maximization and for resource conservation.

Subsurface drip irrigation - past, present, and future.

Abstract 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.