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DIVISION S-4—SOIL FERTILITY & PLANT NUTRITION

Phosphorus Availability under Continuous Point Source Irrigation

^a Arava Res. and Dev., mobile post Eilot 88820, Israel
^b Utah State Univ., Plant Soils and Meteorology Dep., 4820 Old Main Hill, Logan, UT 84322

^* Corresponding author (bengal{at}agri.huji.ac.il).

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION REFERENCES

 
Phosphorous fertigation applied in a microirrigation system provides increased P use efficiency relative to traditional banding. This project investigated the hypothesis that continuous, low-intensity irrigation can provide plants with available P more efficiently than intermittent drip fertigation. Objectives of the study were to characterize water and P distribution when provided to soil by a continuous point source, and to raise P fertilizer efficiency by increasing plant available P without augmenting P application rates through maintenance of relatively constant conditions within the root zone. Plant response, soil P distribution, and soil moisture were compared for an intermittent irrigation regime, giving water for 4 h once every 2 d, to continuous application of the same amount of water in both a water-solute simulation model (Hydrus-2d) and in greenhouse-lysimeter experiments with and without a corn crop on a calcareous sandy loam soil. Results from both the simulation and the lysimeter-soil study showed that the hypothesized zones of increased available P materialized when P-laden water was applied continuously at low application rates to an un-cropped soil. Extractable P concentrations in the soil immediately surrounding the point source were found to be 20 to 25% higher in continuously irrigated soil as compared with pulsed irrigation. After 40 d of growth, corn plants grown under continuous fertigation yielded 20% greater biomass than plants irrigated with the same water quantity and quality once every 2 d. Phosphorus content of corn leaves was 25% greater for the continuous treatment as compared with the pulsed treatment.

Abbreviations: DAP, days after planting

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION REFERENCES

 
IRRIGATION TECHNOLOGIES INVOLVING high-frequency, low-intensity patterns of soil wetting including continuous, low flow water application provide increased growth, transpiration, yields, and increased crop water-use efficiency (Rawlins and Raats, 1975; Segal et al., 2000; Kramer et al., 2001). Rawlins and Raats (1975) combined plant physiological considerations and soil physical principles to give early testimony to the potential benefits of high-frequency irrigation through the effective use of water, land, and fertilizer resources. The positive effects on plant growth were attributed to near-constant conditions in the root zone allowing plants to grow roots in areas with favorable water, oxygen, nutrient, and salt concentrations (Rawlins and Raats, 1975; Bravdo et al., 1992; Clothier and Green, 1994; Glenn, 1999). Thus, uptake of water and nutrients was optimized, as replenishment of soil water adjacent to active roots was maximal and constant. As a result, advantageous conditions for plant growth were exploited. Vegetative and reproductive growth benefited from either the conditions themselves or the lower energy allocated to growing new roots to find water and nutrients. The benefit of applying water and nutrients at high frequencies is suspected to be due in large part to responses occurring while plants are small, before roots systems are fully developed (Segal et al., 2000).

Continuous, low-application irrigation can potentially provide crops with their exact temporal evapotranspiration needs. Irrigation systems could feasibly be designed to respond to environmental conditions such as actual soil water status and to apportion water according to needs or use at all times. Such a system has the potential to minimize both excess application of irrigation water and unnecessary leaching to ground water, resulting in savings of water and reduction in contamination of soil and water resources. Implementation of such systems is not trivial as substantial engineering and agronomic requirements and limitations must be considered. The physical development of such systems will be left to soil and hydraulic physicists and to the irrigation companies, but we believe that the technologies needed for their success will soon be achieved and that an imperative challenge is presented in understanding and managing the chemical processes in soil where such long-term, low-rate application is practiced. The first generation of such products has been developed for greenhouse irrigation and incorporates drippers that close at low pressures. This setup allows systems to be turned on and off without any need to fill pipes with water each irrigation event. The resulting pulsing of small quantities of irrigation water leads to near-constant conditions within the root zone.

Placement and timing of nutrient applications are particularly important in P management. Today, agriculture is challenged to manage P such that production benefits are maximized while adverse environmental effects are minimized (Higgs et al., 2000). Phosphorous is highly immobile in soils and is often a limiting nutrient. Phosphorus-deficient plants suffer from reduced leaf expansion, reduced surface size, and a reduced number of leaves. Respiration and photosynthesis are both reduced in P-deficient plants (Hoppo et al., 1999; Grant et al., 2001). Stress from P deficiency early in growth has considerable negative influence on crop production (Grant et al., 2001). In their review on P nutrition, Grant et al. (2001) emphasize that management practices which provide adequate P early in plant growth are necessary to maximize yields and minimize negative impacts on environmental quality. Several studies of nutrient transport and uptake suggest that maintenance of relatively high moisture and high frequency irrigation lead to greater P mobility and availability (Bacon and Davey, 1982; Mbagwu and Osuigwe, 1985; Bar-Yosef et al., 1989; Kargbo et al., 1991).

Traditionally, P has not been recommended for application through drip irrigation systems. Reluctance in using this practice is based on two arguments: (i) point source application would not succeed in adequately distributing available P because of adsorption to surfaces, and (ii) Ca–P, Mg–P, or Al–P minerals would precipitate both in the drip system and in the soil, causing clogging of equipment and loss of available P. In fact, drip (trickle) irrigation has been shown in a number of studies to be particularly effective in increasing efficiency of P fertilization. Whether the P is applied through the irrigation system or simply made more available through maintenance of high water contents, P concentrations in solution are increased, resulting in increased P mobility to roots (Rauschkolb et al., 1976; Mikkelsen, 1989; Rubiez et al., 1991). In tomato plants, P drip fertigation was shown to result in higher plant tissue-P content than P-banding (Rauschkolb et al., 1976). Higher yield in sweet corn was found with P drip fertigation as compared with preplant P fertilization (Bar-Yosef et al., 1989).

The potential problems of P fertigation of calcareous soils can be avoided by using appropriate P sources, such as phosphoric acid (Bar-Yosef, 1999). Monoammonium and monopotassium phosphate are also potential fertilizers for fertigation but are not as suitable as phosphoric acid due to their lower solubility in water (Imas et al., 1996; Bar-Yosef, 1999). An important result of using drip irrigation systems for P application is that less P fertilizer is generally required to achieve sufficient plant P concentrations compared with other application methods (Bacon and Davey, 1982; Mikkelsen, 1989; Rubiez et al., 1991). Such studies support the hypothesis that continuous P applications in drip irrigation systems will further increase P availability.

Phosphorus transport and uptake are believed to be controlled by diffusion, as sorption and precipitation are dominant in determining P mobility. Results from P nutrition experiments with drip irrigation indicate, however, that convection can play an important role under certain conditions. Mikkelsen (1989) reported increased movement and plant uptake associated with drip-irrigated P compared with other P fertilization methods and attributed the increased mobility to drip application. The extent of P movement, according to Mikkelsen, is dependent on the saturation of soil reaction sites. While P is applied to a limited soil volume near the emitter, it will continue to move with the irrigation water at some rate, depending on the particular soil characteristics. If the drying process is reduced or avoided through high-frequency irrigation, P remains in soil solution and is transported farther into the wetted zone. In an experiment investigating nutrient mixing and uptake as controlled by irrigation frequency and relative humidity, Kargbo et al. (1991) hypothesized that diffusion directly to the root limits P uptake. They discovered, however, that increasing P application frequency resulted in greater P uptake and suggested that the higher P application frequency caused greater mass flow and greater mixing action, leading to the breakdown of regions of immobile P.

Two hypotheses were investigated and are reported here. First, that highly frequent or continuous low-volume irrigation has the potential to maintain three-dimensional distribution patterns of water and nutrients. The second hypothesis was that continuous, low-volume (low-intensity) irrigation from a point source (dripper) offers a means for supplying available P to plants more effectively than traditional water-fertilizer management methods operating with intermittent flow during critical early growth stages when root systems are developing. Water and P movement and distribution were both simulated and measured for a highly calcareous soil receiving either continuous or intermittent applications of water containing P fertilizer in soil columns without growing plants. Water and P movement and distribution, as well as P uptake, plant growth, and yields were measured for sweet corn plants also growing under either the continuous or intermittent fertigation regimes.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION REFERENCES

 
Kidman sandy loam (coarse-loamy, mixed, superactive, mesic Calcic Haploxeroll) was used to represent the hydraulic and chemical properties in the simulations and was used in the lysimeters for the experiments. Characterization of the Kidman soil is found in Dudley et al. (1988)(1991). Initial bicarbonate extractable P in the soil was 3 mg kg^-1. Phosphorus was extracted following the Olsen bicarbonate extractable P method (Pierzynski, 2000) from 2-g soil samples with 40 mL 0.5 M sodium bicarbonate at pH 8.5. Mixtures were shaken for 30 min at 200 cycles min^-1 and filtered through Whatman No. 42 paper. Colorimetric determination of P used ascorbic acid methodology (Eaton et al., 1995).

The P sorption isotherm was determined in the laboratory following Nair et al. (1984). Nine incremental amounts of P as KH₂PO₄ (0, 0.1, 1, 5, 10, 20, 50, 100, and 200 mg P L^-1) were prepared in a background of 50 mM KCl. Two grams of soil, which had been air-dried and passed through a 2-mm sieve, was added to 30 mL of each solution in 50-mL centrifuge tubes and mechanically shaken for 24 h. The soil suspension was centrifuged for 15 min and filtered through a 0.45-µm membrane filter. Each P level was determined in triplicate. The data were fit to a Langmuir sorption isotherm and are shown in Fig. 1 .

View larger version (15K): [in this window] [in a new window]   Fig. 1. Phosphorus sorption isotherm for Kidman sandy loam soil. Symbols are averages of three replicates and the line is the fitted Langmuir equation. C = concentration of P in solution, Q = adsorbed P.

Lysimeters under greenhouse conditions in Logan, UT, were employed to investigate systems similar to those simulated. The lysimeters incorporated highly conductive drainage extensions to maintain hydraulic conditions similar to those in a deep, well-drained soil (Ben-Gal and Shani, 2002). Lysimeters were built in 82.6- by 50.8- by 42.5-cm containers with sufficient volume (120 L soil) to not influence lateral water movement or root growth. With a buried point source (dripper), water containing 70 mg P L^-1 as phosphoric acid was applied continuously or pulsed once every 2 d. Fig. 2 schematically shows an elevated lysimeter with water application and drainage collection systems. Each of six lysimeters was filled with 120 L of Kidman sandy loam soil to reach a bulk density of 1.45 g cm^-3. Irrigation water was applied gravitationally using drip emitters connected to individual Mariotte style reservoirs (Hillel, 1980) for each lysimeter. The lysimeters were brought to field capacity with P-free water before the start of treatments. Evaporation was minimized using plastic mulch and deep drainage was collected, measured, and analyzed for P. By working with the emitters at pressures well below design specifications, flow rates of a little less than 0.1 L h^-1 were possible. A total of 24 L of water containing 70 mg P L^-1 was applied to each lysimeter during the course of 14 d. The continuous treatments were given 2 L of irrigation water every day at 0700 h and took 20 to 22 h for a complete application. Pulse treatments were given 4 L of irrigation every 2 d at 0700 h at a flow rate of 1.5 L h^-1. Emitter flow rates were closely monitored and maintained at a constant level. Soil moisture changes were monitored using tensiometers, and drainage water out of the root zone (35-cm deep) was collected, measured, and routinely tested for P. After 13 d, in the middle of the pulse-irrigation cycle, 42 distinct soil samples were taken from each of the lysimeters. Samples were taken from three depths (0–10, 10–20, and 20–30 cm) along 14 points at 5-cm intervals at right angles radiating from the emitter. Soil was analyzed for moisture, bicarbonate-extractable P, and pH. Six lysimeters were used to obtain three replicates of each fertigation treatment.

View larger version (43K): [in this window] [in a new window]   Fig. 2. Schematic representation of greenhouse lysimeter set-up with gravitational water application and drainage collection.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION REFERENCES

 
Phosphorous Adsorption
The Langmuir equation and the isotherm data show that the soil has a high capacity for adsorbing P and that under agricultural fertilized conditions the amount of P adsorbed is a fairly linear function of the amount of P in the soil solution. Moreover, the adsorption isotherm indicates that saturation of the P sorption sites was unlikely to have occurred under experimental conditions since the solution P and adsorbed (bicarbonate extractable) P concentrations were well within the range of the data in Fig. 1.

Simulated Phosphorus Transport and Distribution—No Uptake
Two-dimensional distribution of water content (Fig. 3) and of soil solution P concentration (Fig. 4) at selected times are given for the simulations. The isoline-distribution graphs reveal that when drying and wetting occurs as in the 2- and 10-d irrigation cycles, P transport fluctuated across time. Moreover, solution P concentrations in the 2- and 10-d cycles were less than those predicted for the continuous application. In the continuous treatment, an area of relatively high P concentration was maintained across time. The 10-d irrigation interval was characterized by sudden wetting of a large portion of the profile immediately following the irrigation event and then gradual, mostly downward movement of the water. Phosphorus was initially high in the immediate vicinity of the emitter, quickly diminished, and ended with maximum levels of 10 mg L^-1 after 10 d. In the 2-d intervals, water content increased across time in a pattern surrounding the emitter that fluctuated as wetting and drying cycles corresponded with each irrigation event. Together with the drying and wetting patterns, P concentration increased around the emitter across time but fluctuated between irrigation applications. Maximum P reached nearly 20 mg L^-1 after irrigation on Day 8 and fell to >16 mg L^-1 before the next irrigation event on Day 10. The continuous regime was characterized by relatively stable zones of water and P as water content slowly increased laterally across time with more downward than lateral movement. Phosphorus concentrations increased around the emitter across time and were consistently higher than in the other irrigation cycles as they maintained maximum P concentrations near 25 mg L^-1_. Distance of P transport was similar for the three regimes. The 10-d treatment initially moved P greater distances, but by the end of the 10 d, the outer boundaries of the P plume were nearly identical for all irrigation cycles. Over time, there was a little more lateral spread of P on the surface of the soil with continuous irrigation regime.

View larger version (38K): [in this window] [in a new window]   Fig. 3. Volumetric water content in soil as modeled in Hydrus-2d at four distinct times during a 10-d simulation for the three irrigation regimes.

View larger version (56K): [in this window] [in a new window]   Fig. 4. Soil solution P concentrations as modeled in Hydrus-2d at three times during a 10-d simulation for the three irrigation regimes.

View larger version (99K): [in this window] [in a new window]   Fig. 5. Measured gravimetric water content, bicarbonate extractable P and 2:1 water:soil pH distribution isocharts after 14 d of intermittent and continuous fertigation on a bare soil. Samples were taken in the middle of the 2-d irrigation cycle.

Uptake of Phosphorus by Young Corn Plants
No significant differences were found between the treatments for water or pH distributions at the end of 42 d with growing corn plants. Volumetric water content ranged from 0.15 at the upper and lower boundaries to 0.13 in the bulk of the soil. The pH ranged from 8.1 to 8.4 with a general gradient from lower to higher pH from the surface to the bottom soil boundary. Bicarbonate-extractable P in the intermittent treatment averaged 4.3 mg kg^-1 with a range from 4.0 to 5.0 mg kg^-1 and a zone of greater than 4.5 mg kg^-1 within 10 cm of the emitter. Bicarbonate extractable P in the continuous treatment ranged from 3.5 mg kg^-1 to 4.3 mg kg^-1 and averaged 3.8 mg kg^-1, only slightly greater than pre-fertigation levels (3 mg L^-1).

Biomass production of corn plants harvested after 15 and 30 d of continuous or 2-d pulsed P fertigation treatments are shown in Fig. 6 . The continuous treatment resulted in 20% greater biomass for leaves (P = 0.91) and stems (P = 0.94). This difference in biomass was observed for both harvest dates. Some of the plants had begun male flower development at the time of the second harvest. No difference was found in flower development, size, or extent between the treatments. Root wet weight density distribution shown in Fig. 7 mainly characterizes roots of a single plant situated directly in the sampling transect. Dry weights of roots for both treatments averaged 7% of wet weights and no spatial patterns were evident for root water content. Plants removed at the first harvest date were expected to have little influence on the root density distribution, as their shoot biomass was <10% of that of the plants at the second harvest. While the continuous treatment yielded 10.5% greater total dry root biomass (P = 0.81), the intermittent treatment had more deep roots and the continuous treatment had a greater density of roots close to the surface.

View larger version (53K): [in this window] [in a new window]   Fig. 6. Sweet corn biomass yields after 26 DAP (top) and 40 DAP (bottom) for 2-d intermittent or continuous fertigation. Y-error bars are standard deviations of three replicates.

View larger version (53K): [in this window] [in a new window]   Fig. 7. Root density distribution isocharts for corn plants receiving 2-d intermittent or continuous fertigation.

View larger version (62K): [in this window] [in a new window]   Fig. 8. Plant tissue P in corn plants fertigated with 2-d intermittent or continuous treatments. Harvest 1 was 26 DAP and Harvest 2 was 40 DAP. Y-error bars are standard deviations.

	CONCLUSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION REFERENCES

 
Continuous application of water and P fertilizer resulted in greater P mobility and higher concentrations of soil solution P surrounding emitters as compared with intermittent application for simulated and experimental studies on bare soil, but not with a corn crop present. An experiment with corn plants resulted in greater biomass production and higher plant tissue P content when water and nutrients were applied continuously as compared with a 2-d intermittent application regime. The increased P uptake and greater P mobility support our hypotheses and suggest that highly frequent or continuous low-volume irrigation can maintain three-dimensional distribution patterns of water and nutrients and provide improved conditions for growth and water and nutrient uptake. Future work should investigate P uptake and effects on growth and yield of an assortment of different crops under continuous fertigation regimes in various soil types. Where continuous fertigation techniques are found practical they can lead to increased yields along with decreased P application rates. In addition to increased efficiency of P fertilization, an important consequence would be a reduction in environmental contamination due to P transport into ground and surface water from agricultural sources.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION REFERENCES

 
Contribution of the Utah Agric. Exp. Stn., Utah State Univ., Logan, UT. Journal paper no. 7496.

Received for publication July 12, 2002.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION REFERENCES

 

• Bacon, P.E., and B.G. Davey. 1982. Nutrient availability under trickle irrigation: I. Distribution of water and Bray no. 1 phosphate. Soil Sci. Soc. Am. J. 46:981–987.[Abstract/Free Full Text]
• Bar-Yosef, B. 1999. Advances in fertigation. Adv. Agron. 65:1–77.
• Bar-Yosef, B., B. Sagiv, and T. Markovitch. 1989. Sweet corn response to surface and subsurface trickle P fertigation. Agron. J. 81:443–447.[Abstract/Free Full Text]
• Ben-Gal, A., and U. Shani. 2002. A highly conductive drainage extension to control the lower boundary condition in lysimeters. Plant Soil 239:9–17.
• Bravdo, B.A., I. Levin, and R. Assaf. 1992. Control of root size and root environment of fruit trees for optimal fruit production. J. Plant Nutr. 15:699–712.
• Chen, J.S., R.S. Mansell, P. Nkedi-Kizza, and B.A. Burgoa. 1996. Phosphorus transport during transient, unsaturated water flow in an acid soil. Soil Sci. Soc. Am. J. 60:42–48.[Abstract/Free Full Text]
• Clothier, B.E., and S.R. Green. 1994. Rootzone processes and the efficient use of irrigation water. Agric. Water Manage. 25:1–12.
• Dudley, L.M., J.E. McLean, T.H. Furst, and J.J. Jurinak. 1991. Sorption of copper and cadmium from the water-soluble fraction of an acid mine waste by two calcareous soils: Column studies. Soil Sci. 151:121–135.
• Dudley, L.M., J.E. McLean, R.C. Sims, and J.J. Jurinak. 1988. Sorption of copper and cadmium from the water-soluble fraction of an acid mine waste by two calcareous soils. Soil Sci. 145:207–214.
• Eaton, A.D., L.S. Clesceri, and A.E. Greenberg. 1995. Standard methods for the examination of water and wastewater. 19th ed. APHA/AWWA/WEF, Am. Public Health Assoc., Washington, DC.
• Enfield, C.G., and R. Ellis. 1983. The movement of phosphorus in soil. p. 93–107. In D.W. Nelson et al. (ed.) Chemical mobility and reactivity in soil systems. SSSA Spec. Publ. 11. ASA and SSSA, Madison, WI.
• Glenn, D.M. 1999. Physiological effects of incomplete root-zone wetting on plant growth and their implications for irrigation management. HortScience 35:1041–1043.
• Grant, C.A., D.N. Flaten, D.J. Tamasiewicz, and S.C. Sheppard. 2001. The importance of early season phosphorous nutrition. Can. J. Plant Sci. 81:211–224.
• Higgs, B., A.E. Johnston, J.L. Salter, and C.J. Dawson. 2000. Some aspects of achieving sustainable phosphorus use in agriculture. J. Environ. Qual. 29:80–87.[Abstract/Free Full Text]
• Hillel, D. 1980. Fundamentals of soil physics. Academic Press, San Diego, CA.
• Hoppo, S.D., D.E. Elliot, and D.J. Reuter. 1999. Plant tests for diagnosing phosphorus deficiency in barley (Hordeum vulgare L.). Aust. J. Exp. Agric. 39:857–872.
• Imas, P., B. Bar-Yosef, I. Levkovich, and M. Keinan. 1996. Orthophosphate solubility in waters of different ionic composition. Fert. Res. 44:73–78.
• Johnson, G., W. Raun, H. Zhang, and J. Hattey. 1997. Oklahoma soil fertility handbook. 4th ed. Oklahoma State Univ., Stillwater, OK.
• Kargbo, D., J. Skopp, and D. Knudsen. 1991. Control of nutrient mixing and uptake by irrigation frequency and relative humidity. Agron. J. 83:1023–1028.[Abstract/Free Full Text]
• Kramer, S., E. Margolit, and E. Kenig. 2001. A new irrigation technology: Continuous irrigation. (In Hebrew). Ann. Rep. Southern Arava Res. Dev. Arava R&D, Yotvata, Israel.
• Krishnamurty, K.V., E. Shpirt, and M.M. Reddy. 1976. Trace metal extraction from soils and sediments by nitric acid-hydrogen peroxide. At. Absorpt. Newsl. 15:68–70.
• Mansell, R.S., S.A. Bloom, B. Burgoa, P. Nkedi-Kizza, and J.S. Chen. 1992. Experimental and simulated P transport in soil using a multireaction model. Soil Sci. 153:185–194.
• Mbagwu, J.S.C., and J.O. Osuigwe. 1985. Effects of varying levels and frequencies of irrigation on growth, yield, nutrient uptake and water use efficiency of maize and cowpeas on a sandy loam ultisol. Plant Soil 84:181–192.
• Mikkelsen, R.L. 1989. Phosphorus fertilization through drip irrigation. J. Prod. Agric. 2:279–286.
• Nair, P.S., T.J. Logan, A.N. Sharpley, L.E. Sommers, M.A. Tabatabai, and T.L. Yuan. 1984. Interlaboratory comparison of a standardized phosphorus adsorption procedure. J. Environ. Qual. 13:591–595.[Abstract/Free Full Text]
• Notodarmojo, S., G.E. Ho, W.D. Scott, and G.B. Davis. 1991. Modeling phosphorus transport in soils and groundwater with two-consecutive reactions. Water Res. 25:1205–1216.
• Pierzynski, G.M. (ed.) 2000. Methods of phosphorous analysis for soils, sediments, residuals, and waters. Southern Cooperative Series Bull. 396. [online]. [110 p.] Available at: http://www.soil.ncsu.edu/sera17/publicat.htm (modified 3 Dec. 2001; cited 12 May 2002; verified 16 Jan. 2003). North Carolina State Univ., Raleigh, NC.
• Rauschkolb, R.S., D.E. Rolsten, R.J. Miller, A.B. Carlton, and R.G. Burau. 1976. Phosphorus fertilization with drip irrigation. Soil Sci. Soc. Am. J. 40:68–72.[Abstract/Free Full Text]
• Rawlins, S.L., and P.A.C. Raats. 1975. Prospects for high-frequency irrigation. Science (Washington, DC) 88:604–610.
• Rubiez, I.G., J.L. Stroehlein, and N.F. Oebeker. 1991. Effect of irrigation method on urea phosphate reactions in calcareous soils. Commun. Soil Sci. Plant Anal. 22:431–435.
• Segal, E., A. Ben-Gal, and U. Shani. 2000. Water availability and yield response to high-frequency micro-irrigation in sunflowers. [CD-ROM]. [7 p.] Proc 6th Int. Micro-Irrigation Congr., Cape Town, South Africa. 22–27 Oct. 2000. Int. Council Irrig. Drainage, New Delhi, India.
• Simunek, J., M. Sejna, and M.Th. van Genuchten. 1999. Hydrus-2d/Meshgen: Simulating water flow and solute transport in two-dimensional variably saturated media. Int. Ground Water Modeling Ctr., Golden, Colorado.

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Ben-Gal, A. Articles by Dudley, L. M. Search for Related Content PubMed Articles by Ben-Gal, A. Articles by Dudley, L. M. Agricola Articles by Ben-Gal, A. Articles by Dudley, L. M. Related Collections Soil Fertility and Productivity Nutrients Nutrient Management Phosphorus