Agricultural Water Management 147 (2015) 34–42 Contents lists available at ScienceDirect Agricultural Water Management jou rn al hom epage: www.elsevier.com/locat e/agwat Effect of different fertilization and irrigation methods on nitrogen uptake, intercepted radiation and yield of okra (Abelmoschus esculentum L.) grown in the Keta Sand Spit of Southeast Ghana E. Oppong Danso a,∗ , S. Abenney-Mickson a , E.B. Sabi a , F. Plauborg b , M. Abekoe d , Y.O. Kugblenu e , C.R. Jensen c , M.N. Andersen b a Agricultural Engineering Department, Faculty of Engineering Sciences, University of Ghana, Legon, Accra, Ghana b Department of Agroecology, Faculty of Science and Technology, Aarhus University, Tjele, Denmark c Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Taastrup, Denmark d Soil Science Department, College of Agriculture and Consumer Sciences, University of Ghana, Legon, Accra, Ghana e Crop Science Department, College of Agriculture and Consumer Sciences, University of Ghana, Legon, Accra, Ghana a r t i c l e i n f o Article history: Available online 28 August 2014 Keywords: Drip irrigation Sprinkler irrigation Fertigation Sandy soil Animal manure a b s t r a c t Three seasons’ experiments were conducted in the Keta Sand Spit to test if current use of sprinkler irrigation and animal manure can be substituted by water saving drip fertigation with reduced P supply to okra. The treatments compared were: (i) irrigation by sprinkler, fertilized with manure spread, (ii) irrigation by sprinkler, fertilized with localized manure, (iii) irrigation by drip, fertilized with localized manure, (iv) irrigation by drip, fertigated with N–K chemical fertilizers (twice during the crop season in the first experiment, weekly in the second and third experiment). Nitrogen uptake, crop interception of solar radiation, yield and water productivity were compared among treatments. The crop did not respond well when fertigation was done only twice, probably due to N-leaching. However, in the second and third experiments, when fertigation was done weekly for eight weeks, the yield of drip fertigated okra was as high as or better than sprinkler irrigated okra with manure spread on the soil, sprinkler and drip with localized manure. In the second experiment, though nitrogen applied was the same (89 kg N ha -1 ), for all treatments, the highest N uptake, intercepted radiation and water productivity were obtained under drip fertigated treatment and these parameters were significantly (P ≤ 0.05) higher than the other treatments. Under sprinkler irrigation, yield was higher with localized manure compared to manure evenly spread on the soil, even though the difference was not significant during the last season. The economic optimal crop N-uptake was estimated to be 125 kg ha -1 independent of season and adequate N-supply seemed especially important for ensuring sufficient light interception during the fruiting stage of okra. Drip irrigation treatments saved almost 30% of water compared to sprinkler irrigation. Therefore, drip irrigation with frequent fertigation allow reduced P-load and more efficient use of nitrogen, water and radiation than with sprinkler irrigation. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The Keta Sand Spit is an important vegetable producing area along the Southeast Coast of Ghana. The region produces fresh market vegetables for the capital, Accra and Togolese markets. The Keta Sand Spit has been a zone of intensive agriculture since the beginning of the 19th century and is regarded as one of the main agricultural areas in Ghana where farming takes place all year ∗ Corresponding author. Tel.: +233 204072401/+233 277810084. E-mail address: sujaniyaayaa@yahoo.com (E. Oppong Danso). round due to irrigation. Most of the vegetable crops grown on the Sand Spit are irrigated and because the soils are coarse-textured, the farmers apply excess amount of irrigation water to avoid yield reduction. The aquifers in the Keta basin are faced with over abstraction (Bannerman, 1994; Helstrup et al., 2007; Jorgensen and Banoeng- Yakubo, 2001) due to the over withdrawal for irrigation. However, abstraction of large volume of water from the shallow aquifer results in salinization through sea water intrusion (Kortatsi and Agyekum, 1999). This has increased the importance of imple- mentation of water conservation practices in irrigated agriculture in the Keta Sand Spit. Adopting drip irrigation and quantitative http://dx.doi.org/10.1016/j.agwat.2014.07.029 0378-3774/© 2014 Elsevier B.V. All rights reserved.