Yield Losses Due to Weeds, Critical Period for Weed-crop Competition in Fenugreek (Trigonella foenum-graecum L.) 

Fenugreek (Trigonella foenum-graecum L.), is an important condiment and seed spice crop of North Western part of India during rabi season. It is native of South Eastern Europe and South Western Asia and mainly cultivated for seed as well as for its leaves (fresh or dried). The seeds are used as a spices and condiments to enhance the flavour and the nutritional value of foods (Choudhary et al., 2017). Seeds have strong odour and slight bitterness in taste and used as seasoning agent for pickles and vegetables. It is mainly grown in India, Morocco, Bulgaria, Pakistan, Afghanistan, Lebnan, Spain, Egypt, Turkey, Algeria. India occupies prime position among the fenugreek growing country of the globe with 1.22 lakh ha and 1.89 lakh tonnes production during 2018-19 (Anonymous, 2019). Rajasthan and Madhya Pradesh are main fenugreek producing states of India. Other fenugreek producing states in India are Gujarat, Haryana, Chhattisgarh, Andhra Pradesh, Telangana, Uttar Pradesh, Uttaranchal. Rajasthan and Madhya Pradesh produce about quite 80% fenugreek seed of the country. Recent studies indicated that fenugreek seeds substantially contain the steroidal substance diosgenin which is used as a base material in the synthesis of sex hormone in oral contraceptives. Fenugreek is grown for its dried ripe fruit and the seeds have pleasantly bitter taste and a peculiar odour and flavor of its own.
       
Weed populations reduce crop yields by influencing the pattern of crop growth and development throughout the season and by directly competing with the crop for limiting precious resources, like light, water or nutrients.  A number of the factors that influence magnitude of crop yield losses from weed interference include the timing of weed emergence relative to the crop, weed density, pattern of weed growth and development. Weed management is one among the foremost critical factors influencing crop yield.  By providing a window of weed-free growth early within the season, the size advantage that crop seedlings have over weeds can be utilized to reduce the intensity of direct competition for resources at the stages of crop development when yield is being determined. Weeds are identified as a significance drawback since they create biotic stress in realizing the genetic yield potential of this valuable crop. Weeds offered maximum competition up to 25-30 days of sowing in fenugreek leading to drastic reduction in seed yield (Tripathi and Singh 1994). The higher weed population density, causes limitations for water, food and their presence along crop plants increases competitions among the plants for nutrients, water and light, finally reduce performance of the crop in terms of economic produce. The amount of yield loss due to weed interference, depends on the crop plant, weeds and growing conditions are quite different. Heavy infestation of weeds throughout the entire growing period may cause an entire loss of crop. Weed were found major hurdle in fenugreek production and mechanical removal of weed is laborious, time consuming and costly if not managed timely. Hand weeding may be a common method of weed control adopted by farmers. The problem assumes added significance due to non availability of adequate labour during peak period of operation specially weeding operations and farmers are going to be forced to delay the weed management activities due to paucity of labour. Therefore, the present investigation was under taken to seek out losses in seed yield of fenugreek with the presence of weeds, to identify critical stage of weed crop competition in fenugreek and most effective stage (crop period) for weed control practice to be adopted in fenugreek by the farmers to reduce the yield losses and enhance the economic returns.

Site characteristics
 
A field experiment was carried out at experimental farm of ICAR- National Research Centre on Seed Spices, Ajmer, Rajasthan in Rabi season from 2010-11 to 2014-15. The location lies on 74°35' 39" to 74°36' 01" E longitude and 26°22' 12" to 26°22' 31" N latitude at an altitude of 460.17 m above mean sea level. This region falls under agro climatic zone III of Rajasthan, India. The average annual rainfall of this region is 540 mm with a mean maximum temperature of 21.71-33.81°C and minimum temperature 2.43 - 18.83°C during growing season. The soil texture at the experimental area was sandy loam having pH(8.2) and EC (1.3 mmhos/cm) with 0.21% organic carbon and 172.5,  32.6 and 244.1 kg/ha available N, P₂O₅  and K₂O, respectively.
 
Experimental design and treatments
 
There were 14 treatments comprising of initial weedy periods of 15, 30, 45, 60, 75, 90 days after sowing (DAS) and weed free period upto 15, 30, 45, 60, 75, 90 DAS along with weedy till harvest (un-weeded check) and weed free till harvest (weed free check). The treatments were replicated three times in a randomized block design. Weed density and their dry weight were recorded by putting a quadrate (0.25 m²) at a random spot in each plot as per treatment and the data were converted to 1.0 m².
 
Crop management
 
Fenugreek variety RMt-1 was sown in second week of November during rabi seasons keeping row to row spacing 30 cm using 20 kg seeds/ha. A uniform dose of 20.0 kg N and 30 kg P₂O₅/ha and 20 kg K₂O/ha was applied as per recommended dose of fertilizers to satisfy the nutritional requirement of the crop. Half dose of N + full P and K was drilled at the time of sowing and remaining half N was applied at the time of first irrigation.
 
Weed observations
 
To work out the weed count per unit area, a quadrant of size 0.5 x 0.5 m (count/0.25 m²) was thrown randomly at one place in every plot and weeds were uprooted for population count at 15, 30, 45, 60, 75, 90 DAS and at harvest and converted biomass g/1.0 m² and weed count as no/1.0 m2 area. In weedy check treatment, weeds were allowed to grow throughout crop growth period. The uprooted weeds were sun dried completely till reached to constant weight and eventually the dry weight was recorded for each treatment. The experiment comprising of 14 treatments including weedy check and weed free condition throughout growth period and laid out in Randomized Block Design (RBD) with three replications.
 
Weed control efficiency
 
The weed control efficiency was computed at different stages as well as at maturity using following formula suggested by Kondap and Upadhaya (1985).
 
Where,
WCE= Weed control efficiency (%).
DWC= Dry weight of weeds in control plots (weedy check). DWT= Dry weight of weeds in treated plot.
 
Weed index (%)
 
weed index (WI) or weed competition index is defined as the reduction in yield due to presence of weeds in comparison to weed free plots. Weed index was worked out on the basis of formula suggested by Gill and Kumar (1969).                                                 
 
Where
X = Yield from weed free plot.
Y = Yield from treated plot for which WI was worked out.
 
Crop growth and yield attributes
 
The plant height (cm) of randomly selected plants from each plot was measured at harvest. The plant height was measured from ground level to the leaf/flower. The number of primary and secondary branches from five randomly selected plants from each plot was counted at harvest. The average was computed and expressed as number of primary and secondary branches per plant at harvest. Pod length, number of pods/plant, number of seeds/pod was also recorded at harvest.
 
Crop productivity and profitability
 
After threshing and winnowing, clean seed obtained from individual plot were weighed and the weight was recorded in kilogram (kg) per plot, then converted to kg per hectare (kg/ha). To ascertain the economic feasibility of various treatments, economics of treatment was worked out in terms of net profit per hectare in order that most remunerative treatment might be recommended. This was done by using average treatment yield and prevailing market rate of input and out puts. The average price of the fenugreek seed and straw was  40.0 and  2.5/kg during the growing period. The net return was calculated by subtracting cost of cultivation for each treatment from the gross return calculated based on economic yield. The B: C ratio was computed by dividing gross return with cost of cultivation for each treatment.
 
Statistical analysis
 
All the data obtained with reference to the weed count, weed biomass, crop growth and yield parameters were analyzed separately for each attribute according to the analysis of variance technique of Panse and Sukhatme (1985). The critical differences were calculated to assess the significant differences between treatment means. The weed count and weed biomass data were transformed by √x+1 for calculation of critical difference for significance.

Effect on weed count and weed biomass (dry matter)
 
The weed flora emerged during the experimentation were Cynodon dactylon L., Digitaria sanguinalis L, sedges like Cyprus rotundus L. and broad leaved weeds like Chenopodium album L.; Chenopodium murale L.; Melilotus alba L.; Anagalis arvensis. Grassy, broad leaf and sedges weed population at one representative site from each plot were taken at 15, 30, 45, 60, 75, 90 DAS and at harvesting stage using 0.25 m² quadrate. Among weed count, the major population at all the growth satages (85-90%) were from Chenopodium album and Chenopodium murale.  The weed count and dry matter accumulation decrease with the rise in weed free period from 15 to 90 DAS (Table 1 and 2). With the advancement of crop growth stages after sowing there was considerable decrease in the weed population. At 30 DAS and subsequent growth stages, weed population decreased at all the weedy traetments due to increased plant-weed and weed-weed competition. At harvest the weed population reached to minimum of 172/m² at complete weedy conditions (T₇) from 1119/m² at 15 DAS. Weed free condition up to 60 DAS after sowing did not bring any significant reduction in weed population and weed dry matter accumulation compare to weed free throughout growth period. The observations recorded at all the seven stages shows decreasing trend in the weed population with the increase of crop duration. Weed count decreases with the increase in growth period due to increase plant-weed, weed-weed competition. The maximum weed dry  biomass at harvest was recorded at weedy throughout growth period (918 g/m²), whereas it was lowest at 15 DAS (2.3 g/m²), this might be due to more accumulation of biomass in weed at harvest  when the weed free period extended up to 45 DAS or longer, strong crop canopy cover suppressed new flushes of weed  which emerged at subsequent crop stages thus the crop smothered the late emerging weed which resulted in significantly lower in weed population and dry matter accumulation under the weed free treatment.  Fifteen days after sowing, weed count were in the range of 1149-871/m² with the dry biomass of 1.9-3.3 g/m², whereas at harvest the number of weeds reduce to 172.0/m² at weedy throughout growth period with the weed dry biomass 918 g/m². These findings are in close conformity with Mali and Suwalka (1987) in fenugreek, Zalavadia et al., (1999) in fenugreek, Patel and Mehta (1989) in cumin.
 

 

 
Growth parameters
 
Acute  weed infestation in the plot maintained weedy up to 75 DAS or onwards up to maturity, adversely affected the growth attributing character of fenugreek namely plant height, number of primary branch, number of secondary branch and crop plant dry matter accumulation (Table 3). Keeping the crop free from weeds up to 60 DAS or weedy up to 30 DAS and there after removal of weeds gave better plant height, more number of primary and secondary branches, increased crop dry matter accumulation then weed free up to 75 DAS or weedy up to 45 DAS. The lowest plant height (72.5 cm), number of primary branches (4.03) and secondary branches (1.47) were recorded at weedy throughout growth period, whereas these growth parameters were maximum at weed free throughout growth period of fenugreek. The higher values of all these growth parameters under these treatments might be due to better control of weeds throughout the crop growth period which might have better availability of moisture and nutrients to the crop resulting more favorable condition for crop, consequently crop attained more growth having smothering effect on weed. The lowest value of growth attributes under weedy throughout growth period might be due to severe competition by weed for resources which made the crop plant inefficient to take up moisture and nutrients consequently plant height, dry matter accumulation were adversely affected. These results are in conformity earlier finding in fenugreek (Devine et al., 1993) and in Ajwain (Yogi et al., 2015). The effect of weeds on primary branches was less as compared to that on secondary branches; it may be because the secondary branches needs more space to grow as compared to primary branches, the growth of secondary branches are suppressed by presence of high weed population.
 

 
Yield attributes and seed yield
 
Sevier infestation of weed in the plots maintained weedy for initial 60 DAS adversely affected the yield attributing characters compare to season long weed free condition and weed free up to 60 DAS. Data presented in Table 3 showed that lowest pod length (7.57 cm), number of pods/plant (23.9), number of seed/pod (12.70), test weight (9.73 g), seed yield (560 kg/ha), straw yield (1821 kg/ha) and harvest index (23.63%) were recorded at weedy throughout growth period. Maximum pod length (cm), number of pods/plant, number of seed/pod, test weight (g), seed yield (kg/ha), straw yield (kg/ha) and harvesting index (%) to the tune of 9.47, 41.2, 16.67, 12.60, 2297, 4954 and 31.73 were recorded at weed free throughout growth period. The weed competition adversely affected the yield attributing characters and seed yield of the fenugreek. Weed is an important factor lowering yield of fenugreek, which is responsible for reducing crop growth by two mechanisms. Primarily by giving competition for resources such as space, light, water, nutrients etc and by allellopathy, this involves releasing of toxin into the environment (Bansal et al., 1992). The perusal of data in Table 3 shows that maximum seed yield of 2297 kg/ha was recorded under treatment weed free throughout growth period, where as the yield was lowest (560 kg/ha) in the treatment weedy throughout growth period. Presence of weeds for different period from 15 to 90 DAS significantly reduced the seed yield from 415.7 kg/ha at weedy up to 15 DAS to 1393.7 kg/ha at weedy up to 90 DAS as compared with weed free throughout growth period (Table 4). Presence of the weed for initial 15 DAS reduced the seed yield of fenugreek to the tune of 18.1% as compared to weed free throughout growth period, the treatments weedy up to 30, 45, 60, 75, 90 DAS and weedy throughout growth period reduced the seed yield significantly to the magnitude of 567.3, 801.7, 913.3, 1253.3, 1393.7 and 1736.3 kg/ha, respectively as compared with the treatment T₁₄ (weed free throughout growth period). Keeping the crop weed free up to 15 to 90 DAS reduce the seed yield losses from 817.3 to 134.0 kg/ha as compared to the weed free throughout growth period, this shows that presence or absence of weed at any stage compete with the crop for nutrient, water and reduce the crop yield significantly. If we compare the yield data at weed free throughout growth period to weedy throughout growth period (weedy check), the seed yield losses were 1736.3 kg/ha to the magnitude of 75.6% reduction in the seed yield. Data in Table 4 show that the yield losses in fenugreek increase from 2.95 kg/ha/day at 15 days weed infestation to 12.31 kg/ha/day at 135 days weed infestation. Similarly the yield losses declined from 5.80 kg/ha/day at 15 days weed free period to 0.95 kg/ha/day at 90 days weed free period. Keeping the crop free from weeds up to 30 DAS or weedy up to 30 DAS and there after removal of weeds gave higher number of plant/m², number of umbel/plant, number of umbellate/umbel and test weight then weed free up to 15 DAS or weedy up to 45 DAS or more period, these result are in close conformity with earlier finding of Patel et al., (2007). The increase weed density (Table 1) and their biomass (Table 2) to such an extreme level under weedy check (T₇) might be attributed to uninterrupted growth of weed which ultimately suppressed the growth and yield attributing characters of fenugreek.
 

 
Weed control efficiency
 
Data regarding the effect of different treatments on weed control efficiency are presented in Table 4. Weed control efficiency decreased from 99.7 % at weedy conditions up to 15 DAS to 96.4, 82.3, 63.8, 55.4 and 19.6 to 0.0 at weedy conditions up to 30, 45, 60, 75, 90 DAS and throughout growth period, respectively. Weed control efficiency improved gradually with the increasing weed free period from 15 DAS to 90 DAS. Weed control efficiency improved from 53.9 % with the treatment weed free up to 15 DAS to 100% with the treatment weed free throughout growth period. The higher weed control efficiency under treatments T₁₁, T₁₂, T₁₃ was due to effective control of weeds from the field as weeds were removed manually and likewise under weedy upto 45 DAS, all the weeds were removed manually gave above 80% WCE. The combined effect of hand weeding and smothering effect by the crop canopy coverage over the weeds after 30 DAS resulted in remarkably less dry weight of weeds (Table 2) observed under these treatments were responsible for higher weed control efficiency. These findings are akin to report of Patel et al., (2005) and Mehriya et al., (2007).
 
Weed index (%)
 
The data pertaining to weed index as influenced by different treatments are presented in Table 4. The different treatments exerted their significant effect on weed index. Increase of weedy period from 15 DAS to 90 DAS increased the weed index gradually from 18.0% to 60.6% and reached to maximum 75.5% in weedy conditions throughout growth period. Among the weed free treatments, maximum weed index of the 35.6% was recorded in the treatment weed free up to15 DAS which decreased sharply and reached to zero in the treatment weed free throughout growth period treatment. The higher weed biomass resulted more weed index and lower weed biomass reduced the weed index at harvest. This shows that reduction in the yield of fenugreek was associated with presence or absence of weeds at different growth stages (Table 1 and 2). These findings are in agreement with the results reported by Yadav and Dahama, (2003).
 
Economics and critical period for weed-crop competition
 
Maximum gross return (₹104248/ha), net return (₹67018/ha) were obtained at weed free throughout growth period with the B:C ratio 2.80 among the weed free treatments (Table 4). Weed free period beyond 75 DAS produced higher yield and net returns with positive B:C ratio. Weedy period beyond 30 DAS produced significantly lower seed yield with significantly lower net returns and B:C ratio as compare with weed free period 60 DAS and above these result indicates that increase in fenugreek seed yield would be possible with increasing number of weed free days. Among the weedy treatments weedy up to 15 DAS to 30 DAS and there after removal of weeds also gave higher yield with net return of  ₹ 86109-69149 with B:C ratio 2.70-2.13, when weeds were allowed to compete beyond 30 DAS results of significant reduction in seed yield of fenugreek along with lower net returns were obtained. Hence the present study suggested maintenance of weed free crop up to 45 DAS to achieve better yield as well as higher return.
       
From the data in Table 4 it can be observed that reduction in seed yield of fenugreek was observed greater when weeding delayed from 15 DAS to 75 DAS. When weedy period lasted only up to 15 DAS and there after weed free period up to 90 DAS or more caused signification reduction in seed yield of fenugreek. Therefore, critical period for weed crop competition in fenugreek range from 30 DAS to 45 DAS after sowing. Taking into account the critical period for weed competition, one can go for any method of weed control which will be more effective till the end of critical period this result indicates that increase in seed yield would be possible with increasing number of weed free days. The data presented by Fig 1 reveal that the critical period for weed competition in fenugreek is 32 DAS, where in the quadratic lines of weedy or weed free treatment intersected each other. The critical period for weed control (CPWC) is a key component of an integrated weed management (IWM) program. It is a period in the crop growth cycle during which weeds must be controlled to prevent yield losses. The relative time of crop and weed emergence is perhaps the most important factor influencing the outcome of crop-weed competition.  Although different densities and weed species can influence the magnitude of crop yield losses, weeds emerging at or near the time of crop emergence will have a much greater potential to cause yield losses than those emerging at later stages of crop development. Examining Table 5, it could be noticed that the best model fitted to study the yield of fenugreek response to weed free and   weed competition durations was quadratic that. Therefore, the quadratic model worked well for describing the relationship between  seed  yield  of fenugreek  and  weeds  under  weed  free and weed competition duration. Fig 1 and Table 5 show the effect of time duration of fenugreek crop free from weeds on seed yield. These equations were Y = 0.04x² - 17.241x + 2177.5 for weedy period and Y = -0.0341x² + 11.73x + 1329.7 for weed free period. The relationship between seed yields with the duration of weed free was significant and positive and prediction function with value R² 0.974, but, the relationship between seed yield with the duration of weed competition was significant and negative and prediction function with value R² 0.985, respectively. Therefore, the quadratic model worked well for describing the relation between seed yield of fenugreek and weeds under weed free and weed competition in the growing season. If we predict the seed yield based on the quadratic model (Fig 1 and Table 5) for weed free period model at 0, 15, 30 and 45 days have declined the seed yield losses from 42.04, 34.70, 28.03, 22.02% and reach to 0.0% at 135 days. Similarly, Weed infestation period model predicted the seed yield losses increased from 0.00 at 0 days weed infestation to 11.47% at 15 days weed infestation and further increased to 73.42% seed yield losses in fenugreek at 135 days. The CPWC is useful for making decisions on the need for and timing of weed control.
 

 

The authors acknowledge the Director ICAR- National Research Centre on Seed Spices, Ajmer, Rajasthan for providing opportunity and needful facility to work at NRCSS, Ajmer.