A Long-Term Barley-Based Rotation Trial in a Syrian Mediterranean Agroecosystem: Implications for Crop Yield Sustainability.

Traditional cropping systems in the Mediterranean involve cereals in rotation with fallow to conserve moisture, or other crops. Livestock production is an essential component of the system. With increasing land-use pressure, fallow is being replaced by continuous cropping, which is unsustainable. The 18-year rotation trial from northern Syria (340 mm average annual rainfall) sought to find economic cropping alternatives to continuous cereals. Initially with wheat and mainly with barley, the focus was on forage alternatives with medic (variable grazing intensities) and vetch (grazing, hay, seed) in comparison to fallow and continuous cereals. The cereal phase of the rotation involved nitrogen fertilizer as well as an unfertilized control. While annual grain and straw yields were related to seasonal rainfall over the years of the trial, N had a significant effect with fallow and continuous barley, but only small effects with medic and vetch.

Highest yields were with vetch and fallow, but as fallow yields a crop once every 2 years, the vetch rotation was most productive. Yields from continuous cropping were lowest and declined with time. The trial demonstrated that forages for livestock and cereal production can be successfully and sustainably integrated in the prevailing Mediterranean cropping systems.