Recovery of 15N-Labelled Urea Applied to Wheat (Triticum aestivum L.) in the Ethiopian Highlands as Affected by P Fertilization

• Published in: Journal of agronomy and crop science (1986) Vol. 189; no. 1; pp. 30 - 38
• Main Authors: Gorfu, A, Kühne, R.F, Tanner, D.G, Vlek, P.L.G
• Format: Journal Article
• Language: English
• Published: Berlin, Germany Blackwell Wissenschafts-Verlag 01-02-2003; Blackwell Verlag, GmbH; Blackwell
• Subjects: agroecological zones; Agronomy. Soil science and plant productions; Biological and medical sciences; fertilizer efficiency; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; grain yield; harvest index; highlands; N balance; N uptake; nitrogen fertilizers; Nitrogen, phosphorus, potassium fertilizations; phosphorus fertilizers; soil; soil degradation; soil nutrients; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Triticum aestivum; urea; wheat; East Africa; Ethiopia; Africa; Nitrogen fertilization; Monocotyledones; Isotope labelling; Nutrient recovery; Agricultural soil; Phosphorus fertilization; Nutrient uptake; Nitrogen Isotopes; N balance; Cereal crop; Field experiment; Urea; Nitrogen balance; Mountain; Gramineae; Angiospermae; Spermatophyta; Nitrogen fertilizer; fertilizer efficiency; Triticum aestivum; N uptake
• ISSN: 0931-2250; 1439-037X
• DOI: 10.1046/j.1439-037X.2003.00006.x

Soil degradation and depletion of soil nutrients are among the major factors threatening sustainable cereal production in the Ethiopian highlands. Fertilizer use as a means of mitigating nutrient depletion has become widely accepted. The fate of fertilizer nitrogen (N) applied to a semidwarf bread wheat system was determined in microplots receiving 41 kg N ha(−1) in the form of urea labelled with 5.617 % atom excess (15)N, without and with the application of phosphorus (P) at 20 kg P ha(−1). The study was conducted in three different agro-ecological zones at 2200, 2400 and 2800 m above sea level (masl) (Kulumsa, Asasa and Bekoji, respectively) in the south-eastern Ethiopian highlands. Yield and yield response to N diminished with elevation, while the response to P increased with elevation, with a significant increase in wheat grain yield observed at Bekoji (2800 masl). N harvest index and N use efficiency improved in response to P application at Asasa (2400 masl). Crop removal accounted for 25–64 and 36–64 % of the applied N without and with P, respectively. The corresponding fractions of 15N recovered in the soil ranged from 2.9 to 3.5 % and from 3.2 to 3.7 %, respectively. Recoveries of applied (15)N were 67 and 52 % at Kulumsa and Asasa, but only 25 % at the highest elevation site, Bekoji. Fertilizer P significantly enhanced N recovery at Asasa (60 %) and Bekoji (36 %), but not at Kulumsa, where the soil had a high level of residual P from previous applications. The fraction of (15)N recovered in the soil–plant system was rather low at Bekoji. However, the rate of (15)N recovery was significantly improved (by 37 %) when fertilizer P was added to the soil. Across all locations, the unaccounted 15N may have been lost primarily through denitrification and volatilization.