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 first-order 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.