Dryland winter wheat response to conservation tillage in a continuous cropping system in northwestern Iran

Conservation tillage and straw mulch management could improve soil water storage efficiency and increase the potential in dry climates to plant more intensively than with the traditional crop–fallow system. There is little information on the success of no-till dryland winter wheat (Triticum aestivum L.) production under annual cropping system in Iran. A 3-year experiment was conducted under dryland conditions to determine the influence of conventional and conservation tillage systems on grain yield and yield components of a winter wheat cultivar on a clay loam soil (Vertic Calcixerepts) in the northwest region of Iran. Tillage treatments comprised conventional tillage (CT: mouldboard plow + disk), reduced tillage (RT: chisel plow + disk), minimum till (MT: sweep plow), and no-till (NTss and NTtr: with standing stubble and total residue, respectively). Tillage treatments had significant effect on grain yield of wheat in 2 out of 3 years. Mean grain yield over three seasons was 1.0 Mg ha−1 for CT, 1.3 Mg ha−1 for RT, 1.1 Mg ha−1 for MT, 1.2 Mg ha−1 for NTss and 1.4 Mg ha−1 for NTtr. A similar trend was observed for wheat biomass yields. Average grain yields with RT and NTtr were significantly greater (25–42%) than grain yields using CT treatment. Number of ears per square meter was significantly increased with NT and RT, while number of kernels per ear and ear length only increased under NTtr, compared with CT treatment. Tillage practices had no significant influence on 1000-kernel weight. Year affected grain yield significantly, mainly due to rainfall. Grain yields under NTtr were 70 and 38% higher than yields from CT treatment in a dry year (2000–2001) and in a year with precipitation above the average (2001–2002), respectively, whereas the precipitation use efficiency in the year with precipitation above the long-term average increased two-fold comparing with the dry year. Results from this study indicated that for a dryland continuous winter wheat cropping system, NTtr had higher grain yields (420 kg ha−1) than that obtained with CT system, probably owing to greater water availability.