Yield and Carbon Isotope Discrimination for Wheat, Barley and Lentil under Different Crop Sequences and Water Treatments in Northern Syria

摘要

Improving water use efficiency is the main challenge in areas where water is the main production-limiting factor. This research was con-durted on a research station in northern Syria between 2005 and 2009. The objective was to determine water use efficiency for different crop sequence rotations and the application of different levels of supplementary irrigation. The study used bread wheat (Sham 8 variety), a local lentil variety and barley (Arabic black variety). A randomized complete block design was used, involving six different cropping sequences with three replications and two levels of supplementary irrigation (75 percent and 55 percent of 90 percent of field capacity) and rain-fed as control. Soil water content was monitored using a neutron probe, and evapotranspiration was calculated. Grain samples (for the season 2007-2008 and for the two water treatments only) were used for measurement of grain carbon isotope discrimination (CID, A). Results showed that water treatments had significant (at0.1 percent level) effects with yields increasing (in terms of grain and total biomass) with increasing water use efficiency WUE) as more water became available. Carbon isotope discrimination, as an indirect measurement of transpiration efficiency, differed for different crops, with lentil having the highest range followed by barley and wheat. This suggests that lentil has a high elasticity in terms of transpiration efficiency compared with cereals. Positive relationships between A and yield were obtained, but more important were the slopes of the relationship between yield and CID (kg of yield per unit of CID) for the three crop species, with highest values being obtained for wheat and lowest for lentil. A simulation model for 19yr of growing barleyand wheat showed that there is a higher tendency for shortage of soil water, reaching permanent wilting point in the months of April and May for wheat compared with barley.