Geographical distribution of soil test values in Syria and their relationship with crop response

Abstract

Climate, particularly rainfall, has a dominant influence on soil properties, and consequently on vegetation and land use. In semi‐arid areas of the world, seasonal rainfall and its distribution determines crop yields and may influence soil formation and biological processes that affect soil nutrient availability. Thus, we conducted a fertility survey in northern Syria's dryland zone across a rainfall gradient, from the arid steppe with less than 200 mm/yr to the wetter wheat‐producing areas with up to 715 mm in some years. This involved sampling of five experimental stations, i.e., Maragha (190 mm), Boueidar (223 mm), Breda (263 mm), Tel Hadya (330 mm), and Jindiress (446 mm), and farmers’ fields in the vicinity of these stations. Nutrient distribution with profile depth was also measured on the stations. The most consistent trend with increasing rainfall was a decrease in calcium carbonate (CaCO₃). Similarly, boron (B) tended to be higher in the drier sites, especially in the sub‐soil. Total nitrogen (N) was higher in the uncultivated steppe, with no obvious trend in cultivated areas, while available phosphorus (P) tended to be higher in cultivated areas. However, there was no relationship between rainfall and extractable potassium (K) or micronutrients, but zinc (Zn) and iron (Fe) were generally low in all areas. Trends were less consistent with the site‐specific stations. Management practices, such as cultivation, grazing, and fertilization distort expected relationships between rainfall and soil parameters, but some properties are related to long‐term rainfall. Crop response data from wheat and barley trials in Syria show that rainfall is the dominant yield‐determining factor, with N and P having a lesser influence.