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Baoxin Chang, Benjamin Wherley, Jacqueline Aitkenhead-Peterson, Nadezda Ojeda, Charles Fontanier and Philip Dwyer

and percent green cover in plots and no negative effects on runoff and nutrient movement. However, their benefits did not extend to significant reductions in runoff water volumes or nutrient exports during precipitation events. Fertilizer application

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Warren C. Stiles

Distribution of nutrients was evaluated in samples collected at various depths and distances from drip emitters after 8 years of application. Nutrients applied to soil surface influenced levels mainly in top 40 cm of the soil profile, while fertigation resulted in movement to depth of 80 cm within the wetted zone. NO3-N was increased in 0- to 40-cm depths by soil surface application, but below 40 cm by fertigation. Fertigation increased P in wetted zone to a 40-cm depth. Surface-applied K increased levels in the 0- to 20-cm zone, while fertigation increased K to the 80-cm depth. Zn and Cu were increased to 80 cm by fertigation. Growth and yield indicate soil surface application of fertilizers plus drip irrigation to be comparable to fertigation in most experiments. Fertigation of mature trees on M.7 with K + B for 3 years did not show consistent positive effects on fruit size or color. Responses associated with fertigation appear to be largely attributable to irrigation unless soil nutrient supplies are inadequate.

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G.H. Neilsen, D. Neilsen and F. Peryea

Traditionally, broadcast or foliar fertilizer applications sufficed to improve the nutrition of many irrigated, deciduous fruit orchards in western North America. Recent developments, including adoption of low-pressure, micro-irrigation systems and planting at higher densities (especially for apples), have increased interest in controlled application of fertilizers directly with irrigation waters (fertigation). The possibility of using fertigation to synchronize fertilizer application and plant nutrient uptake seems attractive as environmental concerns to minimize leaching of nutrients (especially N) to groundwater increase. Recent fertigation research in western North America will be reviewed and compared to traditional fertilizer application methods to assess the potential of fertigation to overcome inadequate nutrition. Emphasis will be placed on the use of soil solution monitoring to assess changes in soil NPK status. Tree response will be illustrated by studies in high-density orchards where N, P, K, Ca, B, or Zn have been fertigated.

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Joan R. Davenport, Robert G. Stevens, Kelly M. Whitley and Tanya Winkler

used as a tracer for mobile anionic plant nutrient movement (e.g., nitrate, chloride) in the soil ( Fisher and Healy, 2008 ; Green et al., 2005 ; Izadi et al., 1993 ; Logsdon, 2007 ; Schuh et al., 1997 ; Seo et al., 2005 ) as well as in studies

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Suphasuk Pradubsuk and Joan R. Davenport

nutrient movement between various plant parts was accomplished by calculating the content of each macronutrient within each plant part (dry weight × concentration) divided by the number of days between sampling dates. Table 2. Significance

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Michael D. Dukes, Lincoln Zotarelli and Kelly T. Morgan

Major horticultural crops in Florida are vegetables, small fruit, melons, and tree fruit crops. Approximately half of the agricultural area and nearly all of the horticultural crop land is irrigated. Irrigation systems include low-volume microirrigation, sprinkler systems, and subsurface irrigation. The present review was divided into two papers, in which the first part focuses on vegetable crop irrigation and the second part focuses on fruit tree crop irrigation. This first part also provides an overview of irrigation methods used in Florida. Factors affecting irrigation efficiency and uniformity such as design and maintenance are discussed. A wide range of soil moisture sensors (e.g., tensiometers, granular matrix, and capacitance) are currently being used in the state for soil moisture monitoring. Current examples of scheduling tools and automated control systems being used on selected crops in Florida are provided. Research data on the effect of irrigation scheduling and fertigation on nutrient movement, particularly nitrate, are reviewed. Concluding this review is a discussion of potential for adoption of irrigation scheduling and control systems for vegetable crops by Florida growers and future research priorities.

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Kelly T. Morgan, Lincoln Zotarelli and Michael D. Dukes

Florida is the most important center of processed citrus (Citrus spp.) production in the United States, and all of the crop is irrigated. Irrigation systems include low-volume microirrigation, sprinkler systems, and subsurface irrigation. This review details the relative irrigation efficiencies and factors affecting irrigation uniformity such as design and maintenance. A wide range of soil moisture sensors (e.g., tensiometers, granular matrix, and capacitance) are currently being used for citrus in the state. The use of these sensors and crop evapotranspiration estimation using weather information from the Florida Automated Weather Network in irrigation scheduling are discussed. Current examples of scheduling tools and automated control systems being used on selected fruit crops in Florida are provided. Research data on the effect of irrigation scheduling, soluble fertilizer injection, and soil nutrient movement, particularly nitrate and the use of reclaimed water in Florida, are also reviewed. Concluding this review is a discussion of the potential for adoption of irrigation scheduling and control systems for citrus by Florida growers and future research priorities.

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C.M. Geraldson

The gradient concept is designed with a soluble source of N–K banded on the soil bed surface in conjunction with a continuing source of water that synchronizes the nutrient–water input with rate of removal by the root. By placing the N–K on the surface rather than conventionally in the bed, nutrient movement to the root shifts from mass flow to diffusion. Nutrients that move by mass flow are a function of water requirement and potentially a source of nutritional instability. With the shift to movement by diffusion, nutrients move independently of the water to replace those removed from the gradient by the root. The gradient with a continuing nutritional stability replaces the variable and limited stability potential of the soil. Commercial tomato yields in Florida more than doubled with the shift to the gradient-mulch procedure. A containerized version of the concept (The EarthBox™) has been most successful for the home gardener and substantiates the validity of the gradient. Most innovative procedures with the gradient as the buffer component minimize pollution, require minimal management, and use minimal water with microirrigation or an enclosed system. To better understand the gradient concept and utilize the procedure, it may be necessary to consider the procedure as a nutritional paradigm shift.

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C.M. Geraldson

The conventional nutritional paradigm has been described as an empirical evaluation of how yield varies with nutrient application and is considered as a trial-and-error procedure. The gradient concept shifts the emphasis from variations in fertilizer application to one specific procedure designed to stabilize the ionic composition of the soil solution; thus providing the potential to enhance productivity beyond the limits of the trial-and-error procedure. By maximizing nutrient movement by diffusion and minimizing movement by mass flow (with the water), movement of nutrients and water to the root can by synchronized with removal by the root. A surface source of soluble nutrients (primarily N–K) in conjunction with a constant water table are the basic parameters. With the shift to a gradient-oriented procedure, commercial tomato yields in Florida (1970s) more than doubled. The Earth Box™, made of recycled plastic (manufactured by Laminations, Inc., Scranton, Pa.) is designed to maintain the parameters for a containerized gradient concept. Tomato yields have averaged 6 to 8 kg/plant (two plants/box). With the addition of side air spaces to the original air space between the media and the water table, the average yield increased by 20% to 30% with a maximum of 11.3 kg/plant (Fall 1996). With minimal water (for transpiration only), minimal management (maintaining the water table), minimal pollution (no leaching), and the associated nutritional stability, the containerized gradient concept has the potential to become a universal sustainable production system for the commercial grower as well as the home gardener.

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Jack W. Buxton and Wenwei Jia

Lettuce was produced using a new concept of hydroponics. The system is based on maintaining a constant water table (CWT). Plants grew on a flat surface and obtained the nutrient solution from capillary matting. One end of the mat was suspended in a trough containing the nutrient solution. The distance between the nutrient solution in the trough and the bench top was kept constant with a water level controller. The nutrient solution was resupplied from a larger reservoir. A ground cover on top of the capillary mat provided nutrient movement to the roots but prevented root penetration. Lettuce seedlings, germinated in small plug trays, were placed in holes cut in a 2.5-cm-thick styrofoam sheet. The styrofoam provided seedling support as well as protected the roots. Roots grew on the surface of the ground cover and were easily removed at harvest. The CWT could be adjusted by changing the height of the water level controller. The CWT concept of hydroponic production does not require pumps nor large storage reservoirs. No runoff occurs; the only nutrient solution used is that required by plants and a minimum amount of evaporation from the ground cover surface. Disease potential should be less than in other systems.