Effect of Type and Planting Date of Cover Crops on Weed Population Structure, Morphological Characteristics and Seed Yield of Sunflower (Helianthus annus L.)

Cultivation of cover crops associated with their proper management can be a sustainable alternative to conventional weed control methods. In addition to their beneficial effects on weed control, these plants can improve soil structure and organic matter, increase water holding capacity, control soil-borne diseases, reduce soil erosion, and subsequently enhance crop yields. The use of suitable cover crops and optimizing the planting date can improve the advantages mentioned above, especially desired weeds control. They were considering the importance of sunflower production development and the need to introduce the ecological approaches in weed control; the present study aimed to investigate the efficiency of some cover crops and their optimum planting date, the influence on weed structure population and morphological traits, and sunflower seed yield (cv. Lakumka) under climatic conditions of Galougah city, Mazandaran province.

In order to study some cover crops and their optimum planting date on controlling the weeds in sunflower production, an experiment was conducted in Galoogah city (Mazandaran province, Iran) based on a factorial split-plot arranged in a randomized complete block design (RCBD) with four replications during two growing seasons (including 2016-2017 and 2017-2018). Experimental treatments were considered to cover crops such as wheat, barley, berseem clover, hairy vetch, and different planting dates, including planting two months before, simultaneous, and two weeks after the sunflower planting. Moreover, two treatments without any cover crop cultivations, including with and without weeding, were designed as controls.

The study results revealed that the cultivation of mentioned cover crops, regardless of types and planting dates, had a significant role in weeds control and increasing the seed yield of sunflower. In all treatments, the highest weeds dry matter was observed two months before the sunflower planting treatment. Also, barley cover crop had the lowest weeds dry matter in both experimental years in two months before the sunflower planting. It could maintain the weeds dry matter lower than other cover crops during various stages of sunflower growth. The lowest weed dry matter was observed in simultaneous planting with sunflower for all cover crops. Planting cover crops two weeks after sunflower planting also reduced the weeds dry matter. However, its efficiency was lower than the simultaneous planting of cover crops with sunflower. The highest and lowest sunflower height were observed in the treatments of berseem clover at the same time of planting and in wheat cover crop planting two months before planting of sunflower (181.76 and 105.98 cm), respectively. The highest leaf area index (3.97) was related to berseem clover cover crop in simultaneous planting date with sunflower, which was 14 and 69% more than control treatment without covering crops in weeding non-wedding conditions in two years of experiment, respectively. The lowest sunflower leaf area index was obtained from the wheat cover crop on the planting date two months before sunflower planting (first and second year 0.96 and 1.08, respectively). The highest sunflower dry matter (485.61 g.m-2) was observed in berseem clover cover crop simultaneous with sunflower planting, which was not significantly different from control treatment in weeding conditions. The lowest sunflower dry matter (108.27 g.m-2) was obtained in wheat planting two months before sunflower planting. Finally, the highest seed yield of sunflower was obtained in simultaneous planting of berseem clover with sunflower (2859.06 kg.ha-1), which was 17% higher than the control treatment without any cover crops in weeding condition (2381.1 kg.ha-1).

Simultaneous planting dates of cover crops with sunflower led to seed yield similar to weeding treatment. Even planting of berseem clover and hairy vetch had 17 and 14% enhancement in sunflower seed yield. Therefore, berseem clover cover crop planting simultaneously as sunflower planting, reduced weed growth, and increased seed yield of sunflower, it can be introduced as a solution for optimal sunflower production in sustainable agriculture.