Statistical estimation of time-trends in two-course crop rotations

An assessment of time-trends in yield parameters is essential to the utilization of data from long-term field trials for the comparison of different crop rotations and input regimes, and the identification of sustainable production systems. The barley-vetch rotation established at Breda in northern Syria has provided the basis for estimation of the time-trends in yield data from selected treatments in a two-course crop rotation trial. The model used for the estimation accounts for the effect of rainfall, a major determinant of each annual yield value, and the firstorder autocorrelation structure in the errors arising from the same plot over time. An expression for the minimum number of cycles required to detect a significant time-trend has been obtained. Results from the barley-vetch rotation under two fertilizer regimes have been discussed.