Study on the effects of different tillage method on physical properties of soil and wheat yield in rapeseed - wheat rotation in warm dryland area.

Regarding to the importance of having suitable tillage system for wheat production after rapeseed cultivation, 5 different tillage methods were examined for 5 years (2004-08) at two sites (Gachsaran and Bagmalek) with 4 replicates in randomized complete block design (RCBD). The five tillage treatments were T1= moldboard plow + disk harrow, T2= chisel plow + disk harrow, T3= ciclotiler, T4= sweep + disk harrow and T5= no-tillage. Because of particular soil texture in Bagmalek, T3 modified to semi moldboard plow as well as disk harrow was removed form the all treatments. The studied characteristics were: percentage of germination (Ger %), plant height, number of spike per square meter (Sp/m2), number of seed in spike, biomass, harvest index (HI), thousand kernel weight (TKW) and grain yield. Furthermore, soil bulk density (BD), soil moisture at different growth stages and soil resistance were recorded in 4 depths (0-10, 10-20, 20-30 and 30-40 cm). In Gachsaran, the results of combined analysis showed that the treatments had significant effects on Ger %, Sp/m2, biomass, HI, grain yield as well as soil moisture in 10-20 cm and BD in 0-10 cm depths. Conventional soil tillage treatment (T1) had maximum grain yield (2972 kg/ha in average) and HI, although, the differences were not significant compared with conservative tillage (T3 and T4). In Bagmalek, the results of combined analysis showed that the effect of treatments was significant only for HI. Similar to Gachsaran, T1 with maximum grain yield (2694 in average) tended to increase the grain yield (19 %) compared with conservative tillage (T4). It can be concluded that conventional tillage (T1) tended to increase grain yield in both sites, but yield rise mainly was not significant compared with conservative treatment. Hence, using conservative tillage could be suggested in these two sites because of its advantages over conventional tillage method.