Assessing long- and short-term trends in cereal yields: the case of Chile between 1929 and 2009
Cereal grain yields have increased worldwide during the 20th century as a consequence of plant breeding, improved cultural practices and intensive use of inputs. However, there is evidence that there are differences in yield pattern evolution across countries and cereals. The purpose of this study was to compare trends in the yields of the most commonly produced cereals in Chile, namely wheat, oat, barley, maize and rice, to identify similarities in trends across crops and to estimate long-term growth rates in the yields and their changes over time. Data for wheat, barley, oat, rice and maize yields between 1929 and 2009 were obtained from the Chilean Oficina de Estudios y Políticas Agrarias (ODEPA). A first-order autoregressive (AR1) model with trend was applied to a time series analysis of yield data to estimate the relative rates of yield increase and short-run adjustments to yield progress. There was a break in the time series for wheat, barley and oat in approximately 1980. Following this break, the yields exhibited notable increases, with these three cereals reaching similar yields (4.4-4.7 ton ha-1 in the last decade). The long-term relative rate of yield was approximately 0.6-1% before the break (approximately 1980) and slightly less after the break. Rice yields decreased from the thirties to the sixties and have increased since then. The maize yield was very low before the sixties (< 2 t ha-1) but has since increased steadily, reaching an average of 10.8 t ha-1 in the last decade. Economic and agronomic changes that have taken place in the country explain the break observed in the cereal yield trends.