68 SEPTEMBER 2015 • WORLD AQUACULTURE • WWW.WAS.ORG Results Irrigation suitability test means were compared for the irrigation and control pond water parameters listed in Table 1. A two-tailed, Student’s t test (P<0.05) was used to determine significant difference between parameter means. Potassium and magnesium were more concentrated in catfish pond water than in the irrigation pond. Potassium was categorized as normal for irrigation purposes with concentrations of 5-20 mg/L, and magnesium concentrations were low (< 10 mg/L). Sodium concentration was greater in the irrigation pond as was Sodium Absorption Ratio (SAR), but both were evaluated at low concentrations of < 60 mg/L and < 3 mg/L, respectively. Water with an elevated SAR (>8.0 mg/L) displaces calcium and magnesium in soil and is less suitable for irrigation. Total ammonia nitrogen (TAN) and nitrite was tested weekly with a portable water quality test kit. TAN ranged from 0.5-1.6 mg/L and nitrite concentrations were 0-0.23 mg/L in both ponds. Irrigation provided water essential to corn production during periods with little rainfall. During each irrigation trip, small amounts of nitrogen (754 g/ha), phosphorus (42 g/ha) and potassium (1.24 kg/ha) were delivered to the corn. Yellow corn was harvested during late October, 2014. Corn production for the 13.9 ha irrigated field was 8,047 bushels with an average yield of 579 bushels per ha. The corn crop likely benefitted little from the small amount of nutrients provided by catfish pond water. Catfish were harvested from both ponds at 0.68-1.82 kg/ fish and were sold to fee-fishing operations. No fish mortality or disease was observed in either pond during the project. During the July to mid-September irrigation period, 4,672 kg of catfish were harvested from the irrigation pond and 6,539 kg from the catfish pond. Total catfish harvested from March through September 2014 was 10,954 kg for the irrigation pond and 9,895 kg for the catfish pond. The difference in harvest yield (1,059 kg) between the irrigation and catfish only pond was likely the result of varied seining effort between the ponds and not the water exchange rate. Differences in water quality between the two ponds were slight, indicating that the small volume of well water added to replenish the irrigation pond had minimal effect on fish production. Acknowledgments Many thanks to the late Dr. John Murdock and to Mr. Rick Murdock of Ponderosa Farms for their participation and dedication to this project. Kentucky State University College of Agriculture Food Science and Sustainable Systems provided project funding. Forrest Wynne, State Extension Specialist for Aquaculture, Kentucky State University, Graves County Extension Office, 251 Housman Street, Mayfield, KY 42066, fwynne@uky.edu
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