Long-Term Agronomic Trials from The Mediterranean Region: A Critical Perspective.
John Ryan, ICARDA, P.O. Box 5466, Aleppo, Syria
The goals of long-term cropping systems experiments are varied: some have clearly defined objectives and definite time limits for achieving those objectives, while others are indefinite and are designed to observe system changes that cannot be readily anticipated in the short term. Thus, the term “long-term” is a relative one. All long-term trials should have inbuilt capacity to respond to new developments in agricultural practices in order to maintain their relevance without invalidating the broader goals of defining longer-term trends. Such trials are all the more needed in highly variable environments and under conditions of rapid cultural and economic change. The Middle East region, which is characterized by a Mediterranean-type climate with two seasons, i.e., a wet cool period from November to May in which rainfed cropping is possible, and a long dry period from June to October in which cropping is only possible with irrigation. Such climates exist elsewhere, especially in Australia. South Africa, and California in the USA. Rainfall variability, both between seasons and within seasons, is a feature of a Mediterranean climate. Agriculture in the region to the south and east of the Mediterranean Sea ,i.e., North Africa and West Asia, has been a traditional low-input cereal legume system combined with livestock raising. In the 1970's this farming system began to change due to population growth and consequent land-use pressure; fallow declined to be replaced with more intensive cropping along with mechanization and increased chemical inputs, and irrigation. Inevitable concerns about sustainability were raised. These concerns could only have been addressed by long-term field trials that simulated the new and alternative cropping systems in relation to existing ones, especially involving rotations, tillage and grazing management practices. Sustainability issues that needed to be assessed ranged from the biophysical to the economic ones. Thus, several cropping systems trials were undertaken by the International Center for Agricultural Research in the Dry Areas (ICARDA) at its main station at Tel Hadya near Aleppo in northern Syria and a its sub-stations in different rainfall and temperature zones in Syria and Lebanon. Simultaneously, similar rotation cropping experiments were initiated in other countries of the region, most with common objectives and some conducted collaboratively with ICARDA. While a huge database has emerged from the various trials, along with specific findings for particular trials, some general conclusions emerged. Mono-cropping was not seen as an alternative to fallow, but the introduction of a forage or food legume was biologically feasible and economically attractive in all but the driest sites. While vetch (Vicia sativa) and medic (Medicago) were alternative forages, the latter was poorly adopted by farmers. Of the food legumes, lentils (Lens culinaris) was suitable to drier areas and chickpea (Cicer arietinum) to more favorable ones. Such rotations were also more efficient at using the limited rainfall. No system was successful without adequate fertilization. Most trials showed that cereal/legume rotations contributed to improved soil quality in terms of organic matter and aggregation as well as microbial biomass and soil nitrogen. Similarly, conservations tillage increased soil carbon and decreased energy inputs without reducing crop yields. The impact of animal grazing within cereal/legume rotations is more difficult to quantify but soil carbon tended to increase with zero stubble grazing. The issue of changes in soil C sequestration is of current relevance to mitigation of global warming. While many of the trials conducted at ICARDA are now terminated, some should have been continued, but none are projected for long periods. In hindsight, many lessons have been learned, some of relevance to such trials elsewhere, with implications for future changes in agricultural practices and society as a whole.