Abstract:
Studies of water distribution uniformity and fertigation uniformity with sprinkler irrigation were conducted in a commercial container nursery. The first phase of the study consisted of determining water uniformity for two sprinkler heights. The second phase consisted of determining fertilizer application uniformity for total fertilizer solution injection volumes of 19, 38 and 76 l (5, 10 and 20 gal).
Sprinkler heights of 1.4 and 2.3 m (4.5 and 7.5 ft) yielded equivalent water rates and water distribution uniformity. Concentration of fertilizer in the samples was more uniform with a total injection volume of 76 l (20 gal) than with 19 or 38 l (5 or 10 gal), but the uniformity of fertilizer application was statistically equivalent for all injection volumes.
Significance to the Nursery Industry:
Uniformity of water application is critical to the growth of plants in a nursery. The need for irrigation uniformity is most acute in container nurseries, where rainfall is not a major factor in total water availability. Uniformity of application of fertilizers and pesticides through the irrigation system (fertigation, chemigation) is even more critical. Relatively small deviations in the amount of fertilizer or pesticides applied can cause visual differences in growth response in the plants. This study measured the uniformity of both water application and fertilizer application through a sprinkler irrigation system in a large container nursery.
The conclusion that the two sprinkler heights had the same water uniformity should indicate to nursery operators that uniformity is not sensitive to this factor. The conclusion that the uniformity of fertilizer application was not significantly different at the different injection volumes indicates that the smaller, and thus more convenient, volumes are acceptable; however, there was a trend toward better uniformity with higher volumes. These results provide guidance to nursery operators who are concerned about water and chemical uniformity.
Introduction:
Uniformity of fertilizer application is always important, but it can be difficult to determine when fertilizer is applied through an irrigation system (fertigation). A nursery operator or researcher has no feedback on the uniformity of his fertigation application except plant response, and that feedback is too late to be useful. There are several types of fertilizer injectors in use for fertigation and also different procedures. Common types of injectors use either the venturi principle to draw fertilizer solution into the irrigation supply line, a pump to force fertilizer solution into the irrigation supply line or a proportional meter to inject fertilizer solution into the irrigation supply line. All of those systems inject a uniform concentration of fertilizer solution at a presumably constant rate.
Previous studies by the authors (as yet unpublished) dealing with fertigation through drip irrigation found that distribution uniformity can vary with the rate of injection of the fertilizer solution. In general, the slower the injection, the more uniform was the distribution. Nursery fertigation with large overhead sprinklers uses a far higher flow rate of water than drip systems (approximately 696 l/min [184 gpm] in the nursery in the current study vs. approximately 4.5 l/min [1.2 gpm] in the experimental drip system). It was assumed that there is an interaction between the ratio of injection rate to flow rate and time for injection, but this could not be determined from the drip study alone.
The current project was an attempt to further quantify the relationships among flow rate, injection rate and fertilizer uniformity by testing a high flow rate system in a container nursery.
Two American Society of Agricultural Engineers (ASAE) standards deal with procedures for testing sprinkler uniformity: ANSI/ASAE S330.1 (1) deals with research studies of single sprinklers, and ASAE S398.1 (2) deals with tests of installed multiple-sprinkler systems. Haman and Yeager (6) described a procedure for measuring irrigation rates in a nursery. Haman et al. (5) discussed the concept of uniformity in nursery irrigation and recommended procedures for determining uniformity. Haman and Yeager (7) proposed a rapid means of determining the distribution uniformity in a container nursery based on the low quarter of samples. Haman et al. (4) defined types of efficiency applicable to nursery irrigation and discussed the factors that effect uniformity. Clark et al. (3) discussed injection of chemicals into irrigation systems, but did not discuss the effect of injection time or volume on uniformity of fertilizer application.
The objectives of this study were to evaluate the uniformity of water and fertilizer application from fertigation with overhead sprinklers in a container nursery.
Materials and Methods:
A study of water and fertilizer uniformity from sprinklers was conducted at a large container nursery in southeastern Louisiana. The irrigation facilities and equipment of the nursery were used. The general principles of ASAE S398.1 (2) were used in this study, but limited equipment and site availability precluded conducting fully standardized tests. The tests had to be completed rapidly to allow the nursery to resume use of the site. Therefore, the abbreviated experimental procedures recommended by Haman and Yeager (6) and Haman et al. (5) were used.
Water uniformity from two sprinkler heights was determined first. Tests were conducted on two blocks of 23 sprinklers each. In one block, the sprinklers were 1.4 m (4.5 ft) high, and the height in the other block was 2.3 m (7.5 ft). The sprinklers in each block were arrayed in three lines of 8, 7 and 8 sprinklers, with the middle line staggered between the outside lines. The distance between lines was 12 m (39 ft), and the distance between sprinklers was also 12 m (39 ft). Water pressure was 200-221 kPa (29-32 psi). The sprinklers were Nelson F33 series impact sprinklers (Nelson Irrigation Corp, Walla Walla, WA) with 4.8 x 3.2 mm (3/16 x 1/8 in) nozzles rated at a nominal flow rate of 30.9 l/min (8.15 gpm) for each head, for a total nominal flow rate of 709 l/min (187 gpm) for each block. Rated total throw diameter at (30 psi) was (91 ft).
To determine water uniformity, a 12 m x 12 m (39 ft x 39 ft) grid was set up surrounding the second sprinkler in the middle line. This grid represents the pattern repeated throughout the block (when water from adjacent blocks is included). Twenty-five collection pans were placed in a 5 x 5 grid pattern with 3.0 m (9.75 ft) spacing to match the 12 m x 12 m (39 ft x 39 ft) grid. Each collection pan was 34 cm (13.5 in) in diameter and 3.2 cm (1.25 in) deep. Each test run was 30 min long, and there were three replications. The water collected in each pan was measured, and the mean application rate and coefficient of variation (CV) of each run were determined. Uniformity was calculated from CV.
A test of fertilizer uniformity was then conducted using only the block with 2.3 m (7.5 ft) high sprinklers. For this test, collection pans were arranged into two grids, one surrounding the second sprinkler in the center line and one surrounding the sixth sprinkler in the center line, thus giving an indication of variability at both ends of the field. Sixteen pans were placed in a 12 m x 12 m (39 ft x 39 ft) grid around each of those sprinklers. The fertilizer was injected using a twin piston pump (Teel # 2P334C) rated at 3.8-7.6 l/min (1-2 gpm) at up to 3,450 kPa (500 psi). Actual delivery rate of the fertilizer solution was approximately 3.8 l/min (1 gpm).
For each test run, the amount of fertilizer required to provide 17 kg/ha (15 lb/a) of N was dissolved in the prescribed amount of water. Blue dye was added to each batch to allow visual monitoring of injection and uniformity. The irrigation system was first stabilized so that all sprinklers were flowing consistently. System pressure was 207-221 kPa (30-32 psi). The total run time was 30 min. This allowed complete injection followed by flushing of fertilizer from the lines.
The samples were analyzed by first recording the total volume per sample and then determining the electrical conductivity (EC) with a Beckman Solu-bridge Conductivity Indicator (model SD-B15, Beckman Instruments, Inc., Cedar Grove, NJ). A calibration equation was empirically developed. A first order regression equation was fitted to the empirical data using CoStat (CoHort Software, Monterey, CA). The r2 value was 0.998. This equation was then used (in a spreadsheet) to convert conductivity readings to grams of fertilizer, which were then corrected based on the sample volumes. The final results were fertilizer rates for each sample location expressed in grams, kg/ha total (lb/a-total), and kg/ha-N (lb/a-N). Concentration of fertilizer in the collected samples was also determined. Coefficients of variation were calculated for each of the data sets. An ANOVA procedure (CoStat) was used to compare the uniformity from each of the test runs.
Results and Discussion:
There were no differences in water rate or water uniformity between the two sprinkler heights (Table 1). The concentration of fertilizer in the samples (based directly on the EC readings) was more uniform with an injected volume of 76 l (20 gal) than with the lower volumes (Table 2); however, when sample data were corrected for water volume, the uniformity of fertilizer application was not statistically different with any of the injection volumes, although there was a trend toward better uniformity with increasing injection volume (Table 2). With the configuration used in this nursery, any injection volume within the tested range will give statistically equivalent results, although the trend is toward better uniformity with larger injection volumes.Table 1. Uniformity of water application from nursery systems.
|
Sprinkler Height, m (ft) |
Water Application Rate, mm/h (in/h) |
Uniformity, % |
|
1.4 (4.5) |
13.2 (0.52) |
81 |
|
2.3 (7.5) |
12.7 (0.50) |
80 |
|
significance |
ns |
ns |
Table 2. Uniformity of fertilizer application from nursery sprinkler systems with different injection times (achieved by dilution of fertilizer and expressed in liters [gallons] of solution injected).
|
Injected Volume, l (gal) |
CV of Fertilizer Concentration, % |
Uniformity of Fertilizer Application, % |
|
19 (5) |
26a |
66 |
|
38 (10) |
20a |
69 |
|
76 (20) |
10b |
75 |
|
significance |
** |
ns |
References Cited:
1. ASAE Standards, 48th Edition. 2001a. ANSI/ASAE S330.1. Procedure for sprinkler distribution testing for research purposes. American Society of Agricultural Engineers, St. Joseph, MI.
2. ASAE Standards, 48th Edition. 2001b. ASAE S398.1. Procedure for sprinkler testing and performance reporting. American Society of Agricultural Engineers, St. Joseph, MI.
3. Clark, G. A., D. Z. Haman, and F. S. Zazueta. 1999. Injection of chemicals into irrigation systems: rates, volumes, and injection periods. University of Florida Cooperative Extension Service bulletin 250.
4. Haman, D. Z., A. G. Smajstrla, and D. J. Pitts. 1996. Efficiencies of irrigation systems used in Florida nurseries. University of Florida Cooperative Extension Service Bulletin 312.
5. Haman, D. Z., A. G. Smajstrla, and D. J. Pitts. 1997. Uniformity of sprinkler and microirrigation systems for nurseries. University of Florida Cooperative Extension Service Bulletin 321.
6. Haman, D. Z. and T. H. Yeager. 1997. Field evaluation of container nursery irrigation systems: measuring application rates. University of Florida Cooperative Extension Service publication AE-261.
7. Haman, D. Z. and T. H. Yeager. 2001. Field evaluation of container nursery irrigation systems: uniformity of water application in sprinkler systems. University of Florida Cooperative Extension Service publication FS98-2.