Evaluation of Growth, Phenology, Yield and Weed Dynamics as Influenced by Integrated Weed Management in Black Rice Cultivars under Nagaland Condition

Rice (Oryza sativa L.) which belongs to the family of Poaceae is an important and extensively grown crop due to its need as a daily food for one of every three individuals on the earth. Of many different varieties of rice known the Black rice variety although having a history of heritage is considered as underutilized crop owing to its limited consumption (Jha et al., 2017). The Manipur black rice also known as Chakhao which has already been awarded the GI tag in the April of 2020 (Moirangthem et al., 2020) is gaining attention to its great nutritive, curative benefits, anti-carcinogenic, anti-inflammatory and anti-oxidative properties. The aromatic, glutinous and purplish black colour of black colour is mainly owing to pigment anthocyanin. Rice is being cultivated in India over a wide range of area with different establishment methods. Irrespective of the establishment methods, it is very well known that the major losses in yield is reported by weed infestation of rice crops (Sheeja and Elizabeth, 2017). Reduction in yield of rice due to weeds in the direct seeded rice field has been reported to about 40-100% (Shekhawat et al., 2020). Control of weeds during critical conditions of crop weed competition in direct seeding of rice (DSR) can be carried out by various physical, chemical or cultural practices (Banik et al., 2020). Additionally, during the crop weed competition, growing of appropriate cultivars is also a need due to its diverse morphological traits, structure of canopy, duration of growth and relative growth rate. Cultivars of rice having weed suppressing characters are an important aspect to manage weed infestations (Kumar et al., 2016). It is for a fact that the cultivars of black rice could provide food security apart from its contribution to interesting diet with many medicinal properties.                              
        
Therefore, conservation of such cultivars is of great importance by carrying out the cultivation through the adoption of better agronomic practices. Keeping in view the need of the above context, an experiment entitled “Evaluation of growth, phenology, yield and weed dynamics as influenced by integrated weed management in black rice cultivars under Nagaland condition” was carried out.

Weed studies
 
A total of 11 weed species namely 3 grasses, 2 sedges and 6 broad leaved weeds were identified and noted from the experimental field. Some of the dominant species were Digitaria sanguinalis, Cynodon dactylon, Cyperus iria, Cyperus rotundus, Borreria latifolia, Phyllanthus niruri, Commelina benghalensis and Alternanthera sessilis.
       
Results on nutrient depletion by weeds showed a significant difference with regard to integrated weed management in both the years of experiment (Table 1). Data revealed that lowest depletion of nitrogen, phosphorous as well as potassium was exhibited under two hand weeding at 15 and 30 DAS and it was followed with sequential application of pretilachlor @ 1.0 kg ha^-1 (PE) fb HW at 40 DAS. (Hassan and Upasani, 2015) and (Nazir et al., 2022) from their findings revealed mutual results leading to lowest depletion nutrients by weeds due to timely control of weeds at the critical stages maintaining a feasible environment for the crops to grow rather than the weeds respectively. Further, weedy check recorded the maximum depletions of the nutrients in both years. Similar findings were also observed by (Sharma et al., 2018) and (Shanmugapriya et al., 2021) where highest removal of nutrients from weedy check may be due to numerous weed growth in these plots that was left unchecked leading to higher weed population as well as dry matter.


 
Growth and yield parameters
 
Variations in data concerned with plant height at harvest, LAI at 60 DAS and biological yield as influenced by integrated weed management in both the years of experiment showed significant results where it was noted that maximum height (110.7 cm), LAI (1.96) and biological yield (5924.83 kg ha^-1) was recorded significantly with two hand weeding at 15 and 30 DAS. Congenial environment owing to lesser crop-weed competition and timely removal of weeds leading to lesser requirement of limited resources favored a better growth of crop with increased canopy development (Mahanta et al., 2019) also confirmed similar opinions from the study conducted. This was closely followed with application of pretilachlor @ 1.0 kg ha^-1 (PE) fb HW at 40 DAS and it may have been due to herbicidal effect that controlled the weeds at early stages while manual weeding at later stages respectively. Mutual results were also confirmed with (Sanodiya and Singh, 2021) and (Bhattacharya et al., 2022). Further, weedy check showed minimum plant height (87.68 cm), LAI (0.86) and biological yield (4066.38 kg ha^-1) respectively in both the years. Similarly, data pertaining to plant height, LAI and biological yield showed variations with different cultivars under study where it was observed that cultivar Chakhao Poireiton exhibited the maximum plant height, LAI and biological yield and was at par with Chakhao Amubi (Table 2). Further, cultivar Wairi Chakhao observed minimum growth and yield attributes in both the years of experiment which was at par with Khurukhul Chakhao. Such differences among the cultivars might have been due to the fact that taller cultivars as well as bigger leaves had the potential smothering effect over the weeds. (Schreiber et al., 2018) from his study also described similar results. However, result observed from plant population under study did not show any significant differences with context to integrated weed management as well as different cultivars under study in both the years.
 


Phenological studies
 
The resulted depicted on Table 3 with regard to phenological studies revealed that it did not show any significant result with context to the four integrated weed management practices under study in the two years of experiment. However, pooled data of days to 50% flowering showed some variations with two hand weeding at 15 and 30 DAS recording highest number of days to 50 % flowering which was at par statistically with pretilachlor @ 1.0 kg ha^-1 (PE) fb HW at 40 DAS, while further data revealed minimum days to 50 % flowering was revealed with weedy check and was seen to be at par with pretilachlor @ 1.0 kg ha^-1 (PE) + bispyribac sodium @ 25 g ha^-1 (PoE) at 20 DAS. Results with regard to the four cultivars of black rice under study showed significant differences on phenological studies where it was seen that significantly maximum days to 50% flowering, physiological maturity as well as maturity was recorded with Chakhao Poireiton which was closely followed with Chakhao Amubi. Additionally, Wairi Chakhao revealed to minimum days to 50% flowering, physiological maturity as well as maturity of crop respectively. Such differences in phenology of crop may have been affected due to condition of environmental during pollination and flowering of the crop. Similar opinions were also revealed in the study conducted by (Purwanto et al., 2020).

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Correlation studies
 
Data from both the year under experimentation showed a strongly negative linear correlation between plant height and nutrient depletion by weeds with coefficient determination of 0.9207 for plant height with N depletion by weed, 0.9128 for plant height with P depletion and 0.9382 for plant height and K depletion which has been depicted in Fig 1, respectively. The result clearly revealed that control of weeds at the critical stages while maintaining a feasible environment for the crops to grow had a positive effect by reduction of weeds leading to lower depletion eventually. Similar opinions were also revealed with the findings from (Saravanane et al., 2016).