Integration of Aquaculture into an Irrigated Farm to Improve Efficiency of Water and Nutrient Use

Integration of Aquaculture into an Irrigated Farm to Improve Efficiency of Water and Nutrient Use

Summary

Objectives
The objectives of this project were to demonstrate the benefits and constraints of multiple uses of water by incorporating fish culture into irrigation waters prior to applying the water to plant crops. Available nutrients such as nitrate and phosphate and organic matter in fish discharge waters were determined from point sources. The effects of the discharge waters on soil nutrient levels, plant fertilizer requirements and plant yields were determined from soil and plant samples. Technical and economic reports documenting the results from different types of integrated systems have been prepared for a diverse audience.

Abstract of Results
Field trials have been conducted to find if integration of aquaculture into irrigated crop production improves efficiency of water and nutrient use. Aquaculture and agriculture have been integrated for greenhouse production of catfish and ornamental plants and for field production of catfish, tilapia, cotton and mesquite.

In systems integrating ornamental production with aquaculture, turf and low disturbance in-situ nursery production were most promising. A series of trials of aquaculture effluent as irrigation water for ornamental horticulture products were conducted. Most of the plants required supplemental fertilizer in addition to the nutrients contained in the aquaculture effluent to achieve optimum growth. This may have been due in part to relatively low nutrient loading rates in most of the experiments. Nitrogen in the effluent seldom exceeded 5 - 10 ppm. The use of high salt geothermal aquaculture effluent directly for nursery irrigation restricted the growth of some species while other presumably more salt tolerant species were not affected.
Use of existing irrigation facilities in established field production systems - storage ponds and conveyance canals - for culturing fish may also provide an economical alternative crop for irrigated field crops, in this case cotton. In our studies, major benefits of integrated systems were dual use of water for two crops, cotton and fish; net increases of NO3-N, PO4-P, and NH3-N to irrigation water via fish effluent; regulatory compliance for discharge water from an aquaculture facility; and enhancement of best management practices resulting in reduced applications of nitrogen. In replicated field trials, cotton yields were not affected, nor were there any differences in soil nutrients, soil organic matter or petiole nitrate between the cotton plots irrigated with fish effluent or standard irrigation water.

In both greenhouse and field crop production systems, aquaculture effluent was found to be suitable for crop production, saving water and adding some nutrients. However, plants generally required supplemental fertilizer in addition to the nutrients contained in the aquaculture effluent to achieve optimum growth.

Economic Analysis
Budget analysis showed a gain in net income of $29 per acre of cotton when tilapia were grown in the irrigation ditches. Net income of the integrated system was $50 per acre with Central Arizona Project irrigation water and $166 per acre with water from wells. Without the government subsidy, cotton production alone and cotton production integrated with fish production were not economic with either source of water. A break-even analysis indicated that the fish price at which the addition of fish production would produce a positive gain in net income over that of cotton alone was $0.50 per pound with the cotton subsidy and $3.40 per pound without the subsidy.

The cotton budgets are based on budgets prepared by the Cooperative Extension Service, College of Agriculture, University of Arizona (Wade, et al. 1993). The fish production portions of the two integrated budgets are based on the results of the fish culture research at the Marana site which provided information on stocking density, survival rate, and feed conversion rate. Aquaculture experts provided information on probable prices, labor, material, and equipment costs. These are preliminary results and should be viewed with caution.

Potential Contributions
Integration of aquaculture and agriculture may improve the cost benefit ratio and environmental impacts of both plant and fish production, especially in the irrigated farmland of the arid Southwest. It may provide an alternative crop, a way to reduce pumping costs, reduce chemical applications and enhance soil health by increasing organic matter and microbial activity, and provide a profitable and environmentally acceptable effluent discharge strategy for fish farmers.

The results of these studies suggest that ornamental plant production can be integrated with aquaculture production. Both high intensity and low intensity ornamental crops and cropping systems were examined and found to be viable as integrated production systems. Of the systems investigated, turf and low disturbance in-situ nursery production were most promising. Turf grew well with aquaculture effluent as irrigation water and offers the advantage of high water consumption. Turf production is however land intensive and is site disruptive.

The use of aquaculture effluent for adapted plant production in a minimally disturbed desert nursery provides the opportunity to utilize this waste in a production system that does not require much land disruption and preserves the native plants and habitats present on the site. Furthermore, production of landscape and land reclamation plant materials with less than optimal nutrients may be desirable since these plants will be utilized in environments with low native fertility and may be better adapted for survival after transplanting.

Nutrients were higher in fish effluent than in well or CAP water in both the pond and canal systems of cotton-fish production systems, but the increases were not large enough to make a difference in the amount of fertilizer that needed to be applied based on best management practices. Because petiole analyses and pre-plant soil analyses were used to establish the amount of chemical nitrogen to be added to fields, the amount of chemical fertilizer applied was reduced by up to 40 percent of the average nitrogen application used by many Arizona cotton farmers in similar soils. Thus, an enhancement of best management practices and additional nutrients added from fish effluent, may result in a substantial reduction in fertilizer application. There had been some concern that fish effluent could add too much nitrogen to soils and actually increase nitrate leaching into the soil profile. Neither of the fish culture systems we used created this problem.

Using the fish pond water or canal water to irrigate crops also alleviates the problem of water disposal from a fish culture facility. Current EPA regulations do not allow disposal of fish effluent into an existing natural waterway. Therefore, using the effluent for crop irrigation prevents the need for special permits or water treatment prior to disposal.

Operational Recommendations
Following best managements practices and integrating small alternative cropping systems can save money and reduce chemical applications. Farmers in the Southwest may have had problems trying to rotate with specialty plant crops, but fish may be an easier alternative. Also, fish farmers should use their discharge water for irrigation, even if for a small area or share the water with a neighboring farmer.

Areas Needing Additional Study
We need to find out why aquaculture has been a difficult industry to develop and integrate into existing cropping systems. Fish culture in these systems also needs to be investigated further. We need to know the effects of field practices such as pesticide applications on the fish, how long fish can stay healthy in a ditch or pond with no water exchange, and the amount of time a farmer must spend on the fish component of the integrated system.
Reported in 1995