Cropping sequence and fertilizer effects on yield and profitability in a wheat-based crop rotation trial in North-western Ethiopia.

A crop rotation by fertilizer rate experiment was conducted from 1994-99 at the Adet Research Center in north-western Ethiopia. The experiment consisted of eight wheat-based cropping sequences, including five of the major break crop species in the surrounding farming system, in factorial combination with four rates of annual fertilizer application. Of the five break crop species, three species _ lupin, field pea and noug _ showed no grain yield response to applied N or P2O5, while two species _ faba bean and tef _ exhibited yield response to both nutrients. Lupin was the highest yielding leguminous crop in the current study, and increased the yield of succeeding wheat crops to a greater extent than any other break crop: wheat following lupin significantly out yielded every other wheat treatment during three season. On average, the first wheat crop following any break crop was higher yielding than the second consecutive wheat crop. The response of wheat grain yield to both N and P fertilizer was highly significant each season. Rotation by fertilizer interactions revealed that the response to fertilizer P was more pronounced in the high-yielding wheat crop following a lupin precursor; wheat following lupin exhibited no response to fertilizer N, suggesting that the enhanced productivity of wheat following lupin may be largely due to N-fixation by the lupin precursor crop. By converting the grain output of all crops grown during the six-year period of conducting the rotation trial to an equivalent monetary value, the economic analysis integrated the current year and residual agronomic effects of crop rotation and fertilizer application. A two-course rotation of noug and wheat with nil fertilizer represented the lowest cost option for farmers in the Adet area. The optimal treatment across the five price scenarios considered in the current analysis consisted of the two-course rotation of faba bean and wheat receiving 60 Kg N and 60 kg P2O5/ha/annum.