Effect of sugar beet (Beta vulgaris) and canola (Brassica napus) residue on weeds, yield and yield components of chickpea (Cicer arietinum)

Introduction Weeds have significant negative effects on agricultural ecosystems. They are responsible for the decline of crop yield because of competition with crops for water, nutrients and sunlight. Existing weed control methods are either expensive or hazardous. Heavy use of chemical herbicides in most integrated weed management systems is a major concern since it causes serious threats to the environment, public health and increase cost of crop production. Therefore, alternative strategies against weed must be developed. Allelopathy is defined as the inhibitory/stimulatory effect(s) of one plant on other plants through the release of chemical compounds into the surrounding environment. It is characterized by a reduction in plant emergence or growth, reducing their performance in the association. Allelopathy provides a relatively cheaper and environmental friendly weed control alternative. This can be considered as a possible alternative weed management strategy. A number of plants have also been known to exhibit allelopathic property on other plants. Allelopathy associated with plants due to the presence of allelochemicals such as monoterpences, phenolic and volatile compounds in their foliage. Therefore, the present study was done to develop management practices to reduce the use of agro-chemicals for sustainable agriculture. Therefore, the effects of allelopathic potential of sugar beet and canola on suppression of some weeds of chickpea farm were studied.   Material & Methods A field experiment based on a randomized complete block design with four replications was carried out in a naturally weeds infested land to investigate the allelopatic effects of canola (Brassica napus L. var Ocapi) and sugar beet (Beta vulgaris Var Jolge) residues on weeds and yield of chickpea (Cicer arietinum) at research center of Shirvan Agricultural College (37° 23¢ north latitude and 57° 54¢ east longitude and altitude of 1060 meters), North Khorasan Province, Iran. Seven treatments including I: chopped residues of canola (1.5 kg m-2), II: chopped residues of sugar beet (1.5 kg m-2) both were separately incorporated to 25 cm depth soil uniformly 20 days before sowing, III: chopped residues of canola and sugar beet mix together (0.75 kg/m2 each), IV: shoot aqueous extract of canola, V: shoot aqueous extract of sugar beetVI: mixed adequate extract of canola & sugar beet, which were separately sprayed at post emergence stage (at 7, 15 and 30 days after sowing) and VII: without any residues and spraying as control. For preparation of aqueous extract, chopped shade dried residues of canola and sugar beet were separately ground into fine powder (using an electric mill). One hundred g of ground tissue of each of the tested species was placed in a 2 L Erlenmeyer flask and 1 L distilled water was added and left for 48 h at room temperature. The mixtures were then filtered through a double layer of cheese cloth followed by Whatman No.1 filter paper using a vacuum pump. Water extracts were applied between rows at the rate of 100 ml per square meter twice at 7 and 14 days after sowing (DAS) using a knapsack hand-sprayer fitted with a flat fan nozzle maintaining a pressure of 207 kpa.   Results & Discussion The result of experiment showed that growth traits of weeds and chickpea plant are significantly affedted by treatments. Maximum inhibition on weed density, weed dry weight, weed coverage (%) and the hight of chieckpea plants were recorded when using sugar beet residues incorporated with soil. So weed density, weed dry weight, weed coverage and the height of chickpea plants decreased by 52.4%, 90.15, 52.6% and 25.2%, respectively, compared to control.  The highest (329.4 g m-2) and lowest (192.1 g m-2) chickpea dry weight were obtained in shoot aqueous extract of canola and shoot aqueous extract of sugar beet, respectively. The highest harvest index (59.2%) observed in plants treated with sugar beet residues. Some studies reported that allelochemicals like salt and drought stresses exhibited inhibitory effects on physiological processes that translate to growth. The effects of allelopathy on germination and plant growth may occur through a variety of mechanisms including reduced mitotic activity in roots and shoots, suppressed hormone activity, reduced rate of nutrient uptake, inhibited photosynthesis and respiration, inhibited protein formation, decreased permeability of cell membranes and/or inhibition of enzyme action. Weed cover reduction can be closely linked to slower leaf production and development of smaller leaves. It was reported that at stress condition leaf area decreases due to a combination of a decrease in cell number and in cell size. A possible reason for dry matter reduction could be the greater reduction in uptake and utillisation of mineral nutrients by plant under allelochemical stress condition. Hegab et al, (2008) found that higher concentration of allelochemical induced inhibitory effect on amylase activity in wheat seedlings. They also reported the application of allelochemicals at high concentrations decreased protein content of wheat seedlings.   Conclusion The present study concludes that integrating canola and sugar beet residues has the potential to suppress weeds germination and growth. These residues can be used as an eco-friendly approach to manage weeds in chickpea fields.