Research Projects
Kenya Project

Subcontract No. RD010A-07

Staff

Auburn University, Alabama

Wesley Wood

US Principal Investigator, Project Leader

Sagana Fish Farm, Sagana, Kenya

Bernard Meso

Graduate Assistant, University of Nairobi (CRSP funded)

University of Nairobi, Kenya

Nancy Karanja	Host Country Co-Principal Investigator
S.M. Kinyali	Host Country Co-Principal Investigator (through January 2000)

Background

Integration of aquaculture and agriculture systems can result in higher productivity of each component. In Kenya fish are grown in both irrigation reservoirs and fish ponds. Farmers may be reluctant to fertilize irrigation water due to a lack of information on the effects of fertilization on irrigated crops. On the other hand, water from fish ponds may be used to irrigate agricultural crops. One goal of the Government of Kenya is to encourage multiple uses of irrigation waters. This investigation was designed to assess the effects of fertilizing irrigation water and of using fishpond effluent to water crops.

Work Plan Research

The following Ninth Work Plan investigation continued into the current reporting period:

• Use of pond effluent for irrigation in an integrated crop/aquaculture system/9ER1. The report submitted for this investigation was a final report.

Note: The methods for 9ER1 have been modified. The revised methods will appear in the Addendum to the Ninth Work Plan. This study is a collaboration among Auburn University (AU), Oregon State University (under MOU No. RD009A), and AU (under Subcontract No. RD010A-08).

Networking

CRSP Effluents and Pollution researchers have hosted over 100 visitors to the Sagana site, including representatives from the Kenyan government's Arid and Semi-Arid Lands (ASAL) project in Laikipia, Kenya. Visitors representing the Ministry of Agriculture have also requested that the researchers continue their drip irrigation work as a demonstration plot for local farmers.

Educational Outreach

Wood is now an adjunct graduate faculty member at the University of Nairobi, Kenya.

Presentations

Meso, B. Application of fish pond effluent to French beans through drip irrigation at Sagana, Kenya. Presented to the Soil Science Society of East Africa (SSSEA) Silver Jubilee (25^th Annual) Conference at Kampala, Uganda, 6–10 September 1999.
Wood, C.W. and C.E. Boyd. Carbon and nitrogen in pond bottom soils. Presented to World Aquaculture 2000 at Nice, France, 2–6 May 2000.

Conferences

The Soil Science Society of East Africa (SSSEA) Silver Jubilee (25^th Annual) Conference at Kampala, Uganda, 6–10 September 1999. (Meso)
World Aquaculture 2000 at Nice, France, 2–6 May 2000. (Wood)

Awards

Bernard Meso was awarded the prize for academic excellence and diversity in soil science at university post-graduate level from the Soil Science Society of East Africa (SSSEA) Silver Jubilee (25^th Annual) Conference at Kampala, Uganda, 6–10 September 1999.

Wood was named a Fellow of the Soil Science Society of America.

Use of Pond Effluent for Irrigation in an Integrated Crop/Aquaculture System

Ninth Work Plan, Effluents and Pollution Research (9ER1)
Final Report

C. Wesley Wood
Department of Agronomy and Soils
Auburn University, Alabama, USA

M. Bernard Meso
Sagana Fish Farm
Sagana, Kenya

Karen L. Veverica
Department of Fisheries and Allied Aquacultures
Auburn University, Alabama, USA

Nancy Karanja
Department of Soil Science
University of Nairobi
Nairobi, Kenya

Abstract

When fish are recovered from ponds, the effluent is often drained, presenting both an environmental challenge and an agricultural opportunity. The effects of irrigation with pond effluent and its interaction with applied fertilizer were assessed in a field experiment using French bean (Phaseolus vulgaris) and kale (Brassica oleracea) over two growing seasons near Sagana, Kenya. Fresh and dry matter yields of the crops were recorded at harvest, and samples were collected for determination of tissue nutrient concentration. In the first season, French bean fresh pod yield differed significantly (P = 0.05) among treatments. Plots receiving canal water and fertilizer at recommended rates had the highest yield (9.1 t fresh pod ha^-1), while those receiving no fertilizer or irrigation had the lowest yield (1.3 t fresh pod ha^-1). In the second season, significant differences (P = 0.05) were observed among treatments in fresh bean pod and fresh kale leaf yields. The highest (4.4 t ha^-1) fresh pod yield was observed in pond-effluent-irrigated and fertilized plots, while the lowest (1.3 t ha^-1) was observed in non-irrigated/unfertilized plots. The highest fresh kale leaf yield (11.5 t ha^-1) was obtained with irrigation with canal water combined with fertilizer application, while the lowest (4.2 t ha^-1) was observed in non-irrigated/unfertilized plots. Low nutrient status in the pond water together with inadequate water supplied to some crops due to emitter clogging was responsible for low yields in treatments where pond water was substituted for canal water. Pond water from the Sagana Fish Farm supplied low amounts of nitrogen (N) and phosphorus (P) for crops, indicating that recommended rates of mineral fertilizers should be used when pond water is used for irrigation. In the second experiment, the effectiveness of two types of soil occurring at Sagana, Kenyaa vertisol (black clay soil) and a cambisol (red clay soil)in retaining nutrients from pond effluent was investigated. A laboratory experiment was conducted with soil columns containing red or black clay soil. Pond effluent application intensities of 31, 81, and 161 mm d^-1 were tested on both soils. Both soils retained over 60% of total P from pond effluents, with red clay soil retaining 27% more P than black clay soil. At the high effluent loading rate, low % N removal was observed in both soils. Total N removal efficiency declined with time after 21 days at the high rate, and after that time no N removal was observed where red clay soil was used. Black clay soil was more enriched by N than red clay soil, while P enrichment was higher in red clay soil than in black clay soil. It appears that land application can remove substantial amounts of P and N from pond effluent.