- Agronomic: rye
- Crop Production: cover crops
- Pest Management: allelopathy, competition, mulches - killed, mulches - living, weed ecology
- Production Systems: holistic management
One of the benefits of cover crops is weed suppression, but the focused management of cover crops for weed suppression is not often considered. A comparison of winter rye cover crop management variables demonstrated that variety, Spring mowing, and nitrogen after Spring mowing can have an impact on the status of the plant tissue at the time of main crop planting. Cover crop management effected growth stage; biomass allocation between stems, leaves and flowers; and allelochemical levels. These changes could be utilized to improve weed suppression and/or enhance the economic incentive for a grower to utilize cover crops.
Tables, figures or graphs mentioned in this report are on file in the Southern SARE office.
Contact Sue Blum at 770-229-3350 or
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The purpose of this project is to study the allelopathic potential of rye (Secale cereale L.) and develop a better understanding of allelochemical biosynthesis within the plant. Cover crops serve a number of purposes including improving soil organic matter, preventing soil erosion, and weed control, among others. Weed control in particular involves both living cover crops and mulches left on the soil surface. This weed control is facilitated by physical suppression, competition, and allelopathy. Allelopathy is the addition of phytotoxic compounds into the soil by an organism, so that the growth of weeds in the close vicinity is reduced. In rye, allelopathy is mainly attributed to the Benzoxazinones (BX), in particular 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA) and its breakdown product benzoxazolin-2(3H)-one (BOA) (Barnes et al. 1987). An allelopathic cover crop, such as rye, can significantly contribute to weed control in an agricultural field (Barnes & Putnam 1983).
The weed control provided by rye cover crops varies significantly from year to year (Nagabhushana et al. 1997). These variations in allelochemical production are potentially due to adverse environmental conditions in the field, such as high temperature or low moisture levels. Differential genetics can also determine different plants' abilities to respond to those unfavorable environmental conditions and might influence their allelopathic potential.
Variations between cultivars are a major source of allelopathic variability; among eight different cultivars a tenfold difference in BX concentrations has been shown (Burgos et al. 1999). Environmental variability also influences BX concentrations and allelopathy, for example plants with low to moderate fertility had higher concentrations than plants with high fertility (Mwaja et al. 1995). In addition, different cultivars vary in their BX concentrations as the plants age, with levels declining concurrently with development of the plants (Reberg-Horton et al. 2005, Rice et al. 2005). Hydroxamic acids are not present in the seed, but rather increase upon germination, peak while the plant is still a young seedling, and subsequently decrease as the plant grows in size (Argandoña et al. 1981).
BX biosynthesis and availability change as rye plants develop (Reberg-Horton et al. 2005, Rice et al. 2005), and BX concentrations are directly related to the phytotoxic ability of the rye plants (Belz & Hurle 2005). However in a field environment, a plant's allelopathic potential for weed suppression is dependent on both allelochemical content of the plant tissue and the total biomass of the plant (Reberg-Horton et al. 2005). Younger plants have a greater BX concentration and thus have greater phytotoxicity. However, younger plants also have less biomass and therefore provide less physical suppression, and a lower total allelochemical dose (kg/ha). Uncertainty exists whether biomass actually affects the weed suppressive characteristics of rye. Wickliffe (1997) found that increased rye biomass did not, or rarely resulted in increased weed suppression, whereas other groups have found correlations between biomass and weed growth suppression (Creamer et al. 1996). Studying the balance between allelopathy and physical suppression is crucial in determining what constitutes an ideal cover crop management plan that maximizes weed control.
So now the question is how do we achieve this? Can we extend the length of time that a rye plant can synthesize BX, or the length of time the BX are available for weed suppression? At what age are different rye varieties most effective at weed control, and is it possible to influence their allelopathic potential through cultural practices? One promising method we are exploring is the development of new rye cultivars with increased allelopathic potential through breeding programs. Other possibilities employ the use of cultural methods such as specific fertilization regimes, use of plant growth regulators, or mowing to increase weed control.
Improving weed control might be achieved by altering various cultural practices. A number of different questions still need to be answered concerning the role of cover corp management on allelopathic potential and the resulting weed control. What effect would changing the planting times have on allelopathic potential? If younger tissue has the greatest weed suppressive ability, would increasing the sowing rate enhance weed control? Re-seeding different varieties is another option that could affect control, planting one variety in the Fall and re-seeding with another variety in the Spring. Perhaps mowing the rye at specific times during the growing season will increase BX concentrations within shoot regrowth. What are the best mowing times, and what varieties are most influenced by mowing? And when is the best time to harvest for mulch? These questions need to be answered so farmers can put different management plans into practice to enhance weed control in their fields depending on their particular situation.
Another possible cultural practice to increase weed suppression is the use of plant growth regulators. Would spraying a plant growth regulator, such as Ethephon, on the rye affect allelopathic compounds in the plant? Previous work in rye has illustrated the potential for induction of BX biosynthesis using the plant defense hormone, jasmonic acid (Slesak et al. 2001). Another hydroxamic acid, HDMBOA-Glucoside, is induced in maize treated with jasmonic acid (Oikawa et al. 2001), as well as by attack by fungal pathogens and insects (Oikawa et al. 2004). Specific cultural methods such as mowing might mimic wounding, and induce defense signal production, and BX synthesis. An understanding of the role plant growth regulators in BX synthesis might potentially allow for the manipulation of the signaling system to increase the level and duration of BX production and improve rye's ability to control weeds.
Our ultimate goal with this project is to develop a viable management plan for farmers to provide maximal weed control in their cropping system. We want to examine several different cultural methods such as variable planting dates, mowing, and fertility to see if we can influence BX availability and allelopathic potential of rye
Field cover crop management treatments will include different Fall planting dates and Spring mowing dates. The impact of N fertilization at mowing will also be considered. The research will also determine if Spring planting of different varieties, particularly late maturing varieties, will affect allelochemical potential of the cover crop mulch. The allelochemical content (BX), growth stage (Feekes) and biomass allocation (dry wt of total tissue per stem and dry wt of leaf and flower tissue per stem).