Effect of subsoiling on some soil physical properties and wheat yield in dryland condition.

In dryland areas, soil tillage should involve soil and water conservation issues and sustainable agriculture and moreover land preparation. In the most dryland cold areas of Iran, tillage operations usually are done in soil with high moisture content especially during spring crops planting. Operations conducted under wet soil conditions in with high clay percent and low organic matter cause compaction and soil structural damage. It was postulated that deep tillage might increase water use efficiency and wheat grain yield. This study was conducted in Zargan, Tajarak and Sararood dry land agriculture research stations on a clay loam soil for 3 years to determine the effect of subsoiling on soil moisture conservation and wheat grain yield in dryland conditions. This experiment was carried out by four treatments including three subsoiler tine spacing (equal, one and half and two times of operating depth) and one evidence treatment (without sub soiling) in randomized complete block design with four replications. Soil bulk density and soil moisture content were measured in the middle of two subsoiler tines in layer 10 cm depth Crop measurements were plant height, spike per/m2, seeds/spike, TKW, Biological and grain yield, harvest index. In Sararood research also station results of combined variance analysis revealed that the wheat yield in different years were different because of difference rate and distribution of precipitation and cold rate of weather in different years. Therefore grain yield in the second year (3003 kg/ha) was highest. Effect of treatments on wheat grain yield and yield components was significant, highest grain yield (2279 kg/ha), biological yield (6022 kg/ha), obtained from plot which subsoiling with the shank space of and 60 cm. In Mamassani area in the province of Fars,results showed that subsoiling decreased the soil bulk density and cone index, and increased water retention in the soil. Results also revealed that applying subsoiler incresead wheat yield and yield components in the dryland conditions. Since subsoiling improves soil physical conditions and increases wheat yield, applying subsoiler in the dryland conditions is recommended. Results of this study also showed that subsoiling with the shank space of 40 and 60 cm had better performance compared to the shank space of 80 cm. On the other hand, shank space of 40 cm reduces the subsoiler effective working width and effective field capacity. Therefore, shank space of 60 cm is recommended for subsoiler in the dryland conditions In Tajarak station results showed that subsoiling with 50 cm shank space decreased cone index, and increased water retention in the soil in depth of 30-50 cm. Results of combined variance analysis revealed that effect of treatments on wheat grain yield and yield components was not significant, but highest grain yield (1363 kg/ha), obtained from plot which subsoiling with the shank space of and 50 cm. Oveall results showed that subsoiling caused soil bulk density reduction and increase soil moisture content and grain yield. Reduction in soil bulk density in the 0 _ 40-cm depth was highest with subsoiling at tine spacings of 40 and 60 cm.