Weed Dynamics and Productivity of French Bean (Phaseolus vulgaris L.) as Influenced by Organic Sources of Nutrients and Weed Management

French bean (Phaseolus vulgaris L.) is a leguminous crop, belonging to the Fabaceae family with chromosome number of 2n = 22. French bean provides direct economic returns to the growers in the form of pods used as a vegetable and grain for human beings as well as fodder for animals. It is considered to be a very rich source of proteins and vitamins and provides carotenoids like beta-carotene, neoxanthin, lutein and violaxanthin required for a healthy diet. It also contains antioxidants which help to scavenge free radicals and also benefits our cardio vascular system (Whankate et al., 2021). Adoption of organic agriculture practices can address the growing global awareness on quality food, good health and safe environment and thus there has been a paradigm shift and interest to adopt organic crop production systems which are ecologically and economically viable and socially justified. Cultivation of crops under organic condition is the positive step for quality food production. Integration of organic sources is the important aspect in nutritional management of the crop for achieving higher productivity, good quality of food and soil health. Use of organic sources of nutrients to meet the nutrient requirement of crops would be an inevitable practice in the years to come for sustainable agriculture, hence organic matter should be replenished by adding organic nutrients. It has been also realised that besides organic nutrient management weed infestation is the major problem. Weed is the major yield limiting factor in crop production and yield losses are high in general and organic culture in particular. Higher infestation of weeds in crop tends to decrease crop yield by increasing competition for water, sunlight and nutrients while serving as host plants for pests and diseases. Organic producers ranked weed management research as their top priority and have many challenges because their weed control tools are mostly limited to cultural methods (Bond and Grundy, 2001), with a strong dependence on excessive tillage, cultivation and hand-hoeing for weed control. Because there are only a few organically approved herbicides, optimizing their application may increase their potential usefulness for organic production systems. Considering the above facts, investigation was carried out to evaluate the organic sources of nutrients and weed management on growth, yield and weed flora of French bean.

A field experiment was conducted at Research Farm of AICRP-IFS, Chatha, SKUAST-Jammu during summer season of 2016 and 2017 in split-plot design with 3 replications. The soil of experimental field was clay loam having initial pH 8.04, organic carbon (0.55%) and available nitrogen (N), phosphorous (P) and potassium (K) of 220.40, 18.25 and 118 kg ha^-1, respectively. The experimental soil was also sufficient in available secondary nutrients i.e.  sulphur (18.75 mg kg^-1) and micronutrients i.e. zinc (0.85 mg kg^-1), copper (0.48 mg kg^-1), iron (27.65 mg kg^-1) and manganese (20.26 mg kg^-1). The treatments consisted of six sources of nutrients in main plot viz. T₁: 50% recommended (Rec.) NPK through fertilizer + 50% N through farm yard manure (FYM) + inorganic source of  micronutrients as per soil test, T₂: 100% Rec. N through different organic sources each equivalent to 1/3 of Rec. N i.e. FYM+ vermicompost + non edible oil cake, T₃: 100% organics (100% Rec. N through different organic sources each equivalent to 1/3 of Rec. N i.e. FYM+ vermicompost + non edible oil cake) + bottle gourd as trap crop for French bean, T₄: 50 % Rec. N through vermicompost + biofertilizers for N + rock phosphate to substitute the P requirement + phosphate solubilizing bacteria, T₅: 100% organics (100% Rec. N through different organic sources each equivalent to 1/3 of Rec. N i.e. FYM+ vermicompost + non edible oil cake) + VAM and T₆: 100 % Rec. NPK + secondary and micronutrients based on soil test through inorganic fertilizer and sub plots comprised of four weed management treatments viz. W0: Weed Free, W₁: Mustard Seed Meal @ 5 t ha^-1, W₂: Rice Bran @ 4 t ha^-1 and W₃: Weedy Check. The inorganic sources used were urea, daimmonium phosphate and muriate of potash to supply N, P and K, respectively. The recommended dose of fertilizers for French bean was 50:100:50 NPK (kg ha^-1). Full quantity of P and K were applied as basal dose and N was applied in split doses. Fifty per cent of N was applied as basal and the rest was applied in 2 equal splits at 25 and 45 days after sowing. Secondary and micronutrients were not applied in inorganic treatments due to their sufficient range in the soil. The organic sources of nutrients used in the experiment were FYM (N, P, K 0.52, 0.23, 0.55%), vermicompost (N, P, K 2.32, 1.15, 1.50%), neem cake (N, P, K 2.89, 0.84, 1.51%), rock phosphate (25.5% P) and biofertilizers such as Azotobacter for supplying N @ 10 kg ha^-1, phosphate-solubilizing bacteria (PSB) @ 10 kg ha^-1 and vesicular-arbuscular mycorrhiza (VAM) @ 5 kg ha^-1. French bean variety ‘Contender’ was sown at a spacing of 60 cm x 20 cm using a seed rate of 80 kg ha^-1. Need based irrigation was given. Mustard seed meal and rice bran were applied as pre-plant incorporation (PPI) 10 days before sowing of French bean. Hand weeding (30 mandays ha^-1) was done in weed free plots with the help of khurpi. A quadrat of 1 m² was used to take observation on species wise weed density and biomass through random sampling in each plot at 60 days after sowing (DAS). The species wise and total number of weeds were counted in each plot separately and analyzed after subjecting the original data to square-root transformation. For weeds dry biomass, species wise weeds were collected at 60 DAS from 1 m² area were dried under the sun and then in oven at 70^oC for 48 h and weighed. Weed control efficiency (at 60 DAS) and weed index were calculated based on the data recorded in French bean as per standard formula (Mishra and Mishra, 1997). Plant height (cm) and dry matter accumulation (g m^-2) were measured at 60 days after sowing of the crop. Number of pods plant^-1, pod length (cm) and average pod weight (g) were recorded during picking of pods. The fresh pod yield was recorded at different pickings from 10.8 m² net plot area. The net returns were computed by deducting the total cost of cultivation from the gross returns as per treatments. While the benefit: cost ratio was calculated by dividing the net returns with the cost of cultivation for different treatments. However, for better understanding, original values of weed density and weed biomass are given in parenthesis. All the data obtained were statistically analyzed using the F-test (Gomez and Gomez, 1984). Critical difference (CD) values at P=0.05 were used to determine the significance of differences between mean values of treatments.

Weed flora
 
Weed flora in the experimental field consisted of narrow leaf weeds viz., Cynodon dactylon, Digitaria sanguinalis and broad leaf weeds viz., Amaranthus spp and sedge weed Cyperus spp during both the years of study.
 
Weeds density and biomass
 
Statistically non-significant results were observed with respect to species wise and total weed density, species wise and total biomass of weeds among different sources of nutrients. However, treatment T5 recorded the lowest species wise and total weed density, species wise and total biomass of weeds (Table 1 and 2). Significant reduction in weed density and weed biomass were observed in weed free plots as compared to weedy check plots (Table 1 and 2). Among the organic weed management treatments, treatment W₁ significantly reduced the species wise and total weed density, species wise and total weed biomass which was however at par with application of W₂ over W₃ treatment. This could be attributed to better efficacy and due to presence of glucosinolates in mustard seed meal and enzymatic hydrolysis to isothiocyanates, thiocyanate, nitriles and other compounds which may be partly responsible for phytotoxic effect and did not allow the weeds to germinate and even resulted in rapid depletion of carbohydrates reserves of weeds already germinated through rapid respiration, senescence of leaves, reduction in leaf area and diminution of photosynthesis process. These results are in close conformity to the findings of Boydston and Al-khatib (2006) and Boydston et al., (2008).
 

 

 
Weed control efficiency
 
Among the organic weed management treatments in frenchbean, treatment W₁ recorded highest weed control efficiency at harvest followed by W₂  in the descending order (Table 3). The higher values of weed control efficiencies in these treatments could be attributed to lower weed population and weed dry weight owing to better efficacy which might have shifted the fulcrum in favour of crop plants and therefore might have resulted in better crop growth over weedy check plots.
 

 
Weed index
 
Among the organic weed management treatments in French bean, W₁ recorded the lowest weed index followed by W₂ in comparison to W₃ plots (Table 3). This can probably be ascribed to improved growth and ultimately yield of crop due to the higher nutrient content by the application of mustard seed meal and rice bran and also as a consequence of effective control of weeds and reduction in the crop weed competition which might have enabled the crop to achieve better resource utilization and can be associated with lower weed count and dry weight.
 
Growth parameters
 
Between the various sources of nutrients, application of treatment T₅ recorded significantly highest plant height and dry matter accumulation which was statistically at par with T₃ and T₂ (Table 4). The significant improvement in growth parameters i.e. plant height and dry matter accumulation might be due to combined application of FYM, vermicompost and neem cake leading to higher availability of nitrogen which improved the plant growth due to the fact that nitrogen after being taken up by the plant is converted in to amino acids which are the building blocks of protein which might have led to increase in the rate of meristematic activity resulting in better growth characters. These results were in close conformity with findings of Sarma et al., (2011). Among the different weed management treatments, W₁ recorded significantly highest growth parameters of French bean i.e. plant height and dry matter accumulation which was statistically at par with W₂ and W₀ treatment. The enhanced growth trend in terms of plant height and dry matter accumulation have happened due to the higher nutrient content of mustard seed meal and better control of weeds leading to efficient utilization of moisture, nutrients, space and light resulting in optimum growth characters. These results are in agreement with the findings of Ibrahim and Mumtaz (2014).
 

 
 
Yield attributes and fresh pod yield
 
Among the sources of nutrients, application of treatment T₅ recorded significantly highest number of pods plant-1, pod length, average pod weight and fresh pod yield of frenchbean which was remained statistically at par with T₃ and T₂ (Table 4). The increase in yield attributes and marked improvement in dry matter accumulation with these treatments might be due to better translocation of assimilates towards sink, which ultimately increase the pod yield of French bean. These results are in conformity with the findings of Singh et al., (2014). Weed management treatments improved all the yield attributes and fresh pod yield of French bean as compared to those observed in weedy check plots (Table 4). Amongst the weed management treatments, W₁ recorded significantly highest number of pods plant^-1, pod length, average pod weight and fresh pod yield of French bean which was statistically at par with W₂ and W₀ treatment. This might have happened due to enhancement in the growth parameters under suitable environment situation provided by substantial reduction in inter-generic competition due to weed suppression and better translocation of carbohydrates for higher sink realization in these treatments. Similar findings were also reported by Ullah et al., (2008).
 
Economics
 
The economic feasibility and usefulness of a treatment can be effectively adjudged in terms of B:C ratio and net returns. Among the sources of nutrients, treatment T₅ registered higher net returns and B:C ratio, owing to higher gross returns as compare to other treatments (Table 3). Amongst weed management treatments, highest net returns and B:C ratio were obtained with weed free treatment. Higher fresh pod yield of French bean in weed free treatment might have been responsible for the highest net returns and B:C ratio. However, treatment W₁ and W₂ recorded the lowest net returns and B:C ratio which was due to higher cost of cultivation in these treatments.

Based on the experimental results obtained from two years of study, it can be concluded that application of 100% organics (100% Rec. N through different organic sources each equivalent to 1/3 of Rec. N i.e. FYM+ vermicompost + non edible oil cake) + VAM  (T₅) produced significantly higher crop yield coupled with organically weed management practice i.e. weed free (W₀) and application of rice bran @ 4 t ha^-1 (W₂) which not only were economically viable and efficient organic weed management options but also kept dominant weeds below threshold level as corroborated with the higher weed control efficiency.

None.