Effect of nitrogen fertiliser applied to tef on the yield and N response of succeeding tef and durum wheat on a highland vertisol

Abstract

A trial was conducted on an Ethiopian Vertisol from 1990 to 1995 to determine the residual effect of fertiliser N applied to tef (Eragrostis tef) following chickpea (Cicer arietinum) on the grain and straw yield, N content, and N uptake of succeeding crops of durum wheat (Triticum turgidum var. durum) and tef. Measures of N use efficiency across the interval 0 to 60 kg ha-1 of applied N contrasted between the two consecutive tef crops: tef following chickpea exhibited lower mean values for agronomic efficiency (AE), namely 11.7 vs 16.8 kg grain per kg applied N, and apparent recovery (AR), 37.8 vs. 66.4%, of N compared to the second consecutive tef crop. The magnitude and consistency of the beneficial carryover effect of N applied to tef on the succeeding tef and durum wheat crops was dramatic. The mean AE of 60 kg ha-1 of N applied to tef and wheat in the current season (using 0 N as the base) was 16.8 and 13.0 kg grain per kg fertiliser N, respectively; the mean AE of 60 kg N applied to tef in the previous season was 6.1 for both crop species. The results demonstrated a residual fertiliser N benefit equivalent to 36.3 and 46.9% of the response to current season N application for tef and durum wheat, respectively (i.e., across the interval from 0 to 60 kg fertiliser N ha-1). Across the same interval, the mean rates of apparent recovery of fertiliser N in tef and wheat were 66.4 and 65.4% for current season N application, and 25.7 and 36.1% for previous season N application. The carryover effects of applied fertiliser N on succeeding cereal crops on Vertisols in the Ethiopian highlands have several beneficial implications. Tef and wheat grain comprise the principal dietary components of the Ethiopian highland populace, while tef and wheat straw represent the major dry season feed source for Ethiopia=s livestock population. The current study demonstrates that the carryover benefit of applied fertiliser N enhanced the yields and N contents of the grain and straw of both wheat and tef, resulting in significant increases in total N uptake. Thus, both human and livestock populations in the Ethiopian highland Vertisol zones would benefit from an increase in dietary protein intake as well as an increase in the quantity of dietary staples. Any analysis of the profitability of fertiliser N response should reflect the multi-year benefit period.