Effect of Different Tillage Methods and Management of Plant Residues on Agronomy Traits of Wheat and Organic Carbon and Nitrogen of Soil in a Three-years Crop Rotation

Conventional tillage methods increase energy costs and lead to the destruction and reduction of water and soil resources, and for a long time, have an adverse effect on soil properties and cause the formation of hard layers. Repeated tillage and deep plowing cause a quick release of carbon dioxide, causing soil and greenhouse effects and, in the long run, undesirable effects on soil characteristics. Compared with conventional tillage, protective tillage reduces the number of agricultural operations, which has many benefits. So that the loss of moisture and destruction of the soil structure would be reduced. Furthermore, the oxidation of organic residues of plants is reduced. Research has shown that the maintenance of a part of the previous crop residues on the surface of soil and the presence of superfluous roots of arable crops in the soil at a rate of two-thirds, reduce the amount of soil compaction in compared with uncoated and unpolluted land. Therefore, the present study was conducted to investigate the effect of different tillage methods and plant residue management on wheat and organic carbon of soil in Mashhad weather conditions.

 This research was carried out as a three-year experiment with wheat –rapeseed - wheat rotation as split plots in a randomized complete block design with three replications. In this design, different tillage methods were considered as the main plot and management of plant residues as a subplot. Tillage methods consist of three levels: conventional tillage (plowing + discing + leveling + farrowing + planting with seeding machine), low tillage (light discing + farrowing + planting with seeding machine), and no tillage (direct sowing with seeding machine). Also, the management of plant residues includes three levels: no residues, 30 percent of plant residues, and 60 percent of the previous crop residues. Characteristics of heading and maturity dates, wheat yield and yield components, and soil organic carbon content were investigated.

The results showed that the longest time for the occurrence of heading and maturity was observed in conventional tillage treatment. So that, it was only in this treatment the heading and maturity stages occurred on dates more than 170 and 202 days after sowing, respectively. Treatment of no residues with 168.22 days after the sowing date had the most extended date of heading. No-tillage treatment significantly decreased the number of spikes per square meter and 1000-seeds weight. However, there was no significant difference between the levels of plant residues in no-tillage treatment. No-tillage significantly reduced the grain yield of wheat. Though in no-tillage conditions and 30 percent of plant residues, grain yield was significantly higher than 60 percent, and no residues were in the same tillage conditions. The highest grain and biological yields were observed in conventional tillage treatments and in 30 and 60 percent of plant residues. Conventional tillage significantly reduced the soil's organic carbon content. Low tillage treatment at 30 and 60 percent of plant residues observed the highest organic carbon and nitrogen.

Although wheat's grain and biological yield in conventional tillage treatments were more than low tillage and no-tillage, low tillage improved the organic carbon content of the soil, and this phenomenon can have a positive effect on plant yield in the long run. Therefore, preservation of 30 percent of rapeseed residues with low tillage in wheat - rapeseed - wheat is recommended.