Agron. Sustain. Dev. 25 (2005) 137-143
DOI: 10.1051/agro:2004065

Effect of fertilizer rate and water irrigation quality on the recovery of ¹⁵N-labeled fertilizer applied to Sudangrass

M.N. Khelil^a, S. Rejeb^b, B. Henchi^a and J.P. Destain<sup>c

a</sup>  Faculté des Sciences de Tunis, Département de Biologie Végétale, 1002, Tunis, Tunisia
^b  Institut National de Recherche en Génie Rural, Eaux et Forêts, Laboratoire de Physiologie Végétale, BP 10, 2080 Ariana, Tunisia
^c  Centre Wallon de Recherches Agronomiques, 4 rue Bordia, 5030 Gembloux, Belgium

(Received 14 April 2003; accepted 4 November 2004)

Abstract - Wastewaters are increasingly used for irrigation of cropping systems in Tunisia. However, to develop environmentally sound practices the contribution of wastewater to crop N nutrition needs to be clarified, especially in cropping systems already receiving mineral fertilizers. For a better understanding of the interaction between fertilizer N and N originating from wastewater, experiments using ¹⁵N were conducted. ¹⁵N-labeled fertilizer was applied at different rates (0, 60, 100 and 140 kg N·ha^-1) and with different water irrigation qualities (tap water or treated wastewater) to sorghum grown in lysimeters during 1998 and 1999. Recovery of ¹⁵N-labeled fertilizer in the above-ground crop at final harvest in treated wastewater irrigation was higher at the lowest rate of fertilizer application (54%), with the amount recovered in the crop increasing as the rate of ¹⁵N-labeled fertilizer application increased up to the rate of 100 kg N·ha^-1. Nevertheless, in spite of this increase in ¹⁵N-labeled fertilizer in the crop, total plant N uptake did not differ between rates. Treated wastewater irrigation had no negative effect on the recovery of ¹⁵N-labeled fertilizer. About 62 and 55% of ¹⁵N-labeled fertilizer was removed by Sudangrass in either tap water or treated wastewater. Neither fertilizer N rate nor water quality had an effect on the ¹⁵N-labeled fertilizer remaining in the soil at final harvest. On average 20% in the wastewater treatment (19-24%) and 30% in the tap water treatment (26-31%) of the ¹⁵N fertilizer applied were in the 0-60 cm layer of soil at final harvest in 1998 and 1999, respectively, and mostly present in the 0-20 cm layer. The proportion of applied ¹⁵N-labeled fertilizer remaining in the soil at final harvest increased with increasing N rates. About 60, 69 and 72% of ¹⁵N left in the soil at final harvest was in the surface 0-20 cm layer. Residual ¹⁵N was greatly higher in soil following the first harvest than after the final harvest, with the greatest value (38%) measured at the lowest rate of ¹⁵N-labeled fertilizer (30 kg N·ha^-1). Losses of ¹⁵N-labeled fertilizer increased with application rate, but were unaffected by water quality irrigation. Approximately 13% of the applied ¹⁵N fertilizer was lost following the application of 100 kg N·ha^-1 with either treated wastewater or tap water irrigation.

Corresponding author: S. Rejeb rejeb.saloua@iresa.agrinet.tn

© INRA, EDP Sciences 2005