Progress 04/01/06 to 03/31/11
Outputs
OUTPUTS: The goal of this project is to determine if reducing irrigation system operating pressure (OP)from 12 to 6 psi could improve drip irrigation management and become a UF/IFAS recommendation for irrigation scheduling. In objective 1 (determine the effect on emitter flow rates, water application uniformity and soil water movement), flow rates for three commercial drip tapes were found to decrease to 0.13-0.17 gph at 6 psi compared to 0.19-0.25 gph at 12 psi without affecting uniformity of irrigation at 100 and 300 ft lateral lengths. Using soluble dye as a tracer, depth (D) of the waterfront response to irrigated volume (V) was D = 4.42 + 0.21V - 0.001V2 (p<0.01, R2 = 0.72) at 6 psi, with a similar response at 12 psi, suggesting that depth of the wetted zone was more affected by total volume applied rather than by OP itself. D went below 12 inches when V was about 45 gal/100ft, which represented about 3 hrs of irrigation at 6 psi and 2 hrs of irrigation at 12 psi for a typical drip tape with flow rate of 0.24 gph at 12 psi. Hence, for the same volume of water applied, reduced OP allowed extended irrigation without increasing the wetted depth. OP also did not affect the width (W) of the wetted front: W = 6.97 + 0.25V - 0.002V2 (p<0.01, R2 = 0.70) at 6 psi. As the maximum wetted width at reduced OP was 53% of the 28-inch wide bed, reduced OP should be used for two-row planting or drip-injected fumigation only if two drip tapes are used to ensure good coverage and uniform application. Reducing OP therefore offers growers a simple method to reduce flow rate and apply water at rates that match more closely the hourly evapotranspiration to minimize the risk of drainage and leaching losses. The second objective studied the possibility of growing a tomato crop with reduced water (100% irrigation rate vs 75%) and nitrogen (N) fertilizer (100% N rate vs 80% and 60%) inputs at reduced OP. In one year, marketable yields were greater at 6 than at 12 psi (753 vs 598 25-lb cartons/acre, p<0.01) with no significant difference among N rates. But in year 2, mkt. yields were greater at 12 psi (1703 vs 1563 25-lb cartons/acre at 6 psi, p=0.05) and 100% N rate (1761 vs 1586 25-lb cartons/acre at 60% N rate, p=0.04). The effect of Irrigation rate was not significant (p=0.59) on tomato mkt. yields in either year with no interaction between irrigation rate and N or OP treatments. This suggests that reduced OP may not be able to provide enough water to meet the needs of a fully growing crop and instead could be more appropriate for use with young plants when water demand is low. For the third objective to determine soil water movement after a cropping cycle, it was found that response to OP was significant (p=0.01) with max. average wetted depths of 52 and 63 inches at 6 psi, and 64 and 67 inches at 12 psi, for the respective years of study. In the presence of plants, water moved in the soil at a lower rate of 0.09 inch/10gal/100ft compared to 0.9 inch/10gal/100ft without plants. However, the waterfront had still moved to about 60 inches at the end of the season, indicating that reduced OP alone was not able to keep irrigated water within the crop rootzone of 12 inches. PARTICIPANTS: This project was a close collaboration between UF/IFAS Horticultural Science Dept. and SARE. UF partners were graduate students, extension specialists and County Exension faculty. Irrigation suppliers, state agencies (Florida Dept. of Agriculture and Consummer Services), BMP Implementation Teams and growers had input in design, execution, and interpretation of results. TARGET AUDIENCES: Primarily growers and regulatory agencies. Secondarily, Exension faculty and irrigation suppliers. PROJECT MODIFICATIONS: Project was conducted and executed as planned.
Impacts
Overall, reducing OP using a commercially available pressure regulator is a simple, practical and inexpensive method to obtain low emitter flow rates that can help reduce water and fertilizer inputs without compromising uniformity in small fields. Based on these results, we propose that UF/IFAS irrigation recommendation specify reducing OP as a practice in irrigation scheduling to improve on-farm water and nutrient management. In the absence of commercial drip tapes with FR <15 gal/100/hr at 12psi, this project has shown that growers can simply increase the irrigation time without seriously compromising uniformy by using an in-line pressure regulator. This allows a longer irrigation time when plants are small and when irrigation is used for establishment and ETc replenishment at the same time. In addition to reduction in water use and decreased risk of nutrient leaching, this project showed potential in considerign reducing fertilization amounts as a reduction in water application rate. Low OP has the potential to become a simple BMP.
Publications
- Poh, B.L., E.H. Simonne, R.C. Hochmuth, and D.W. Studstill. 2009. Effect of splitting drip irrigation on the depth and width of the wetted zone in a sandy soil. Proc. Fla. State Hort. Soc. 122:221-223.
- Bee Ling Poh, Aparna Gazula, Eric H. Simonne, Francesco Di Gioia, Robert C. Hochmuth, and Michael R. Alligood. 2011. Use of Reduced Irrigation Operating Pressure in Irrigation Scheduling. I. Effect of Operating Pressure, Irrigation Rate, and Nitrogen Rate on Drip-irrigated Fresh-market Tomato Nutritional Status and Yields: Implications on Irrigation and Fertilization Management. HortTechnology 21: 14-21.
- Bee Ling Poh, Aparna Gazula, Eric H. Simonne, Robert C. Hochmuth, and Michael R. Alligood. 2011. Use of Reduced Irrigation Operating Pressure in Irrigation Scheduling. II. Effect of Reduced Irrigation System Operating Pressure on Drip-tape Flow Rate, Water Application Uniformity, and Soil Wetting Pattern on a Sandy Soil HortTechnology 21: 22-29.
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Progress 04/01/06 to 03/31/07
Outputs
OUTPUTS: Increasing lateral water movement as an attempt to reduce vertical water movement may help reduce nutrients loss below the root zone of vegetables grown with plasticulture. Because lateral movement of water may be increased with reduced operating pressures (OP), our objectives were to measure (1) the effects of low OP on drip tape (DT) flow rate (FR), (2) the effect of DTFR on depth and width (inches) of the wetted zone using soluble dye. Target OP were achieved with two medium flow pressure regulators (6 and 12 PSI with 4-16 and 2-20 gallons/min. FR, respectively). For objective 1, six treatments were achieved through a combination of commercial DT (12-inch emitter spacing; with 20 (DT1), 24 (DT2), 39 (DT3) gallons/hr/100-ft FR) and OP (12 and 6 PSI). For objective 2, a total of 24 volume of water applied (VW) treatments were achieved through a combination of the above 6 treatments applied at 4 irrigation lengths (45, 90, 180, and 240 minutes). In objective1 treatments had a significant effect on FR, mean FR was significantly higher at 12 PSI OP than at 6 PSI OP (23.61 and 17.96 gallons/hr/100-ft respectively). DTFR significantly affected depth and width of the wetted zone. Contrary to what we expected, depth and width of the wetted zone were significantly higher at 12 PSI OP than at 6 PSI OP. Within the range of VW (6.3 - 93.6 gallons), the relationship between mean width and VW was quadratic (mean width = -0.0007volume2 + 0.17volume + 9.35; R2 = 0.94), and relationship between mean depth and VW was linear (depth = 0.038volume + 22.11; R2 = 0.32). Hence, reducing OP reduces FR but the reduction depends on the DT, but increasing FR increases the lateral movement of water in the soil, which was contrary to what we expected. PARTICIPANTS: This project is supported by a Southern Region-Sustainable Agricultural Research and Extension (SR-SARE)graduate-student grant awarded to Aparna Gazula, PhD Student in the Horticultural Sciences Department at the Unviersity of Florida. TARGET AUDIENCES: Small and large farm vegetable growers PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The project will be repeated next year before it is demonstrated on-farm
Publications
- No publications reported this period
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