Effect of Different Winter Cover Crops on the Dynamics of Weed Populations and Corn Growth (Zea mays L.) (Single 704)

Cover crops have  wide range influence on agroecosystem  as well as multiple benefits for farmers. A major benefit of cover crops is the suppression of weeds during fall and winter, which can help to reduce soil tillage and herbicide use. A cover crop is a plant that is used primarily to slow erosion, improve soil health, enhance water availability, make weeds smother, help control pests and diseases, increase biodiversity and bring a host of other benefits to your farm. Many types of plants can be used as cover crops. Fabaceae, Poaceae and brassicaceae familys are the most extensively used. Considering the importance of corn, this study was conducted to investigate the effect of six types of winter cover crops including rye, barley, hairy vetch, berseem clover, Indian mustard and rocket on the dynamics of weed populations and seedling growth and yield of corn.

To investigate  the efficiency of various cover crops in weed controlling, seedling growth and yield of maize (Zea mays L.) (single-cross 704), a factorial experiment based on Split Block  design was conducted with three replicates in 2016-2017 at research field of Gorgan University of Agricultural Sciences and Natural Resources. Experimental treatments included: 1) cover crop type in 7 levels of rye (Secale cereal L.), barley (Hordeum vulgare L.), hairy vetch (Vicia villosa L.), berseem clover (Trifolium alexandrinum L.), Indian mustard (Brassica junce L.), rocket (Eruca sativa L.) and no cover crop (control), 2) weed elimination in two levels of hand weeding and no-weeding. Different  cover crops planted in three times the recommended amount in middle winter of 2016. One week before planting corn, all cover crops were sprayed with paraquat herbicide (3 liters per hectare), then corn seeds were planted  directly inside the residuals of the cover crops manually.

Comparison of weed density and dry weight in various treatments of cover crop with control treatment shows the potential of cover crop (disregarding the type) in weed control and increment of diversity. The results showed that the growth of maize seedlings planted in hairy vetch and berseem clover (both from Fabaceae family) and rye residue areas (form Poaceae family) had an increasing trend and in Indian mustard and rocket (both from Brassicaceae family) and barley (from Poaceae family) had a decreasing trend. The lowest maize grain yield was obtained in no cover crop treatment, whereas the lowest grain yield among cover crop treatments was achieved in maize planted in barley residue. Indian mustard and rocket residues had the lowest maize yield after barley. It seems that residues  of these three crops have  allelopathic impact on maize, which was confirmed by observing growth reduction in maize seedlings planted in these residues. On the other hand, the highest maize grain yield was associated with rye, hairy vetch and berseem clover treatments. Hairy vetch and berseem clover had lower biomass than rye. It seems: 1) the ability of these plants  in biological nitrogen fixation, 2) improve soil fertility and 3) accelerate the rate of decomposition of these plant  residuals had a significant role to  improve the growth and quick development of maize that planted in  residuals of these plants. Brust et al. (2014) were tested the  growth and weed suppression ability of four new cover crop species including tartary buckwheat, forage radish, red oat and grain amaranth. The results show that tartary buckwheat and forage radish are well suited as new cover crops in Germany due to their fast growth and good weed suppression ability. 

According to the results, barley, Indian mustard and rocket are able to produce high biomass and have very good effects on weed control. However these plants also have allelopathic effects on corn seedling. Therefore, they are not recommend for cultivation in corn. Rye, hairy vetch and berseem clover had less biomass, but had a good ability to control weeds. It also improved seedling growth and corn yield. Therefore, these three plants can be described as suitable cover crops in corn.