Effect of Different Tillage Practices and Canola Cover Crop on Yield, Yield Components of Sunflower and Soil Quality Indicators in Dastjerd region (Hamedan)

Suitable tillage methods and planting cover crops are such factors in sustainable agricultural systems, which play an important role in the sustainability of agricultural production systems. The benefits cover crop can be referred improvement of soil fertility, chemical properties of soil, increasing of soil organic matter and biodiversity and finally increasing of crop yields.
This study was conducted at Agricultural Research Station of Bu-Ali Sina University in Dastjerd village near the city of Hamadan located in the west of Iran during 2015 growing season. A factorial layout based on a randomized complete block design with three levels of tillage practices (no-tillage (NT), minimum tillage (MT) and conventional tillage (CT)) and two levels of cover crops (with (UC) and without (NC) canola as a cover crop) was conducted. Treatments were replicated in three times. After harvesting main crop (sunflower), selected soil quality indicators including organic carbon, total nitrogen, available phosphorus and available potassium were measured. In addition, yield components of sunflower including percentage of unfilled grain, grain weight, number of grain per anthodium, anthodium diameter, grain and biological yields were measured at the end of the season. The data were analyzed by SAS software. Means were compared using Duncan's Multiple Range test at P≤0.05.
The results indicated that organic carbon and macronutrients (NPK) of soil were the highest in MT × UC treatment. After the minimum tillage treatment, the highest amounts of soil quality indicators were measured in the treatment of non-tillage treatment and presence of cover crop. MT×UC treatment with 1.04% organic carbon was significantly higher than other treatments and the lowest organic carbon (0.56%) was measured in conventional tillage treatment without using cover crop. The highest amount of macro-nutrients (nitrogen (0.16%), phosphorus (24 mg kg-1) and potassium 430 (mg kg-1) were revealed at the MT × UC treatment. In comparison with the conventional tillage, the minimum tillage treatment increased sunflower grain weight by about 18%. NC treatment reduced sunflower grain weight by 19% compared to UC treatment (using cover crop). The maximum anthodium diameter (27 cm) was achieved at MT×UC treatment, while this treatment resulted in an increase of 55.5% in anthodium diameter compared to CT×NC treatment. The number of grain per anthodium was not significantly different between the two treatments of MT×UC and NT×UC. Minimum tillage compared to conventional tillage significantly increased sunflower grain yield. Sunflower grain yield was decreased by 53% in non-using cover crop treatment compared to UC treatment (using cover crop). The highest (1043.3 g m-2) and the lowest (715.6 g m-2) biological yield of sunflower were obtained in minimum tillage and conventional tillage treatments, respectively. Between cover crop treatments, sunflower biological yield in NC treatment was 10.5% lower than UC treatment. Minimum tillage with the conservation of residue helps to protect the soil surface and increases soil quality. Therefore, conservation tillage is one of the new methods for optimum soil use as the most important supply of food sources and can play an important role in increasing farm productivity.
In summary, the results suggested that the highest and the lowest sunflower yields were belonged to MT×UC and CT×NC treatments, respectively. In justifying these results, it can be said that planting cover crops, especially when combined with conservation tillage systems, improves soil organic matter and soil nutrient elements and increases sunflower yield.