Effect of weed management practices and nitrogen levels on nutrient uptake of rice and weeds under drum seeded rabi conditions

Introduction

Rice is a major staple food crop and plays a vital role in food security and livelihood generation in India. Due to increasing scarcity of water and labour, drum-seeded rice is gaining importance as an alternative to conventional transplanting because of its lower labour requirement, reduced production cost and efficient resource utilization. However, severe weed infestation is a major constraint in drum-seeded rice, as weeds compete with the crop for nutrients, moisture, light and space, resulting in considerable yield reduction (Chauhan and Johnson, 2011 and Mahajan et al., 2021) [1,9] . Weeds grow rapidly and absorb nutrients more efficiently than rice during the early growth stages, leading to higher nutrient depletion and lower nutrient use efficiency (Rao et al., 2017 and Yadav et al., 2022) [15,20] . Effective weed management practices, particularly integration of herbicides and mechanical weeding, help in reducing weed biomass, nutrient removal by weeds and improving nutrient uptake by the crop. Herbicides such as pretilachlor, pyrazosulfuron-ethyl, penoxsulam and cyhalofop-butyl are widely used for effective control of grasses, sedges and broad-leaved weeds in rice ecosystems (Kumar et al., 2018 and Ramesha et al., 2023) [7,14] . Nitrogen, being the most important yield-limiting nutrient in rice, enhances the growth of both crop and weeds. Excess nitrogen application without proper weed control may increase weed growth and nutrient depletion, whereas optimum nitrogen management coupled with effective weed control improves crop competitiveness, nutrient uptake and productivity (Mahajan and Chauhan, 2015 and Singh et al., 2021) [8/, 17] . Several researchers have also reported increased uptake of nitrogen, phosphorus and potassium under efficient weed management and higher nitrogen levels due to better crop growth and dry matter accumulation (Nayak et al., 2015, Reddy and Ameena, 2021 and Prakash et al., 2022) [10,16,13] . However, information on the combined influence of weed management practices and nitrogen levels on nutrient removal by weeds and nutrient uptake by drum-seeded rabi rice is limited. Hence, the present investigation was undertaken to study the effect of weed management practices and nitrogen levels on nutrient removal by weeds and nutrient uptake by drum-seeded rabi rice.

Materials and Methods

During rabi 2020-21 and 2021-22 at College farm, PJTAU, Rajendranagar an experiment was taken on loamy sand soil, which is slightly alkaline in reaction and non-saline, with low in organic carbon and available nitrogen, medium in phosphorus and high in potassium. The experiment treatments consists of four weed management practices (F1) viz., W 1: Unweeded (control), W 2: Pretilachlor 6% + Pyrazosulfuron-ethyl 0.15% GR 615 g ha -1 as pre emergence (PE) fb Penoxsulam 1.02% + Cyhalofop butyl 5.1% OD 120 g ha -1 as post emergence (POE), W 3: Pyrazosulfuron-ethyl 70% WDG 21 g ha -1 as PE fb Penoxsulam 1.02% + Cyhalofop butyl 5.1% OD 120 g ha -1 as POE, W 4: Pretilachlor 6% + Pyrazosulfuron-ethyl 0.15% GR 615 g ha -1 as PE fb mechanical weeding 25 and 50 DAS and four nitrogen levels (F2) viz., N 1 -No nitrogen (control), N 2 -75% recommended dose of nitrogen (RDN) (112.5 kg N ha -1 ), N 3 -100% RDN (150 kg N ha -1 ), N 4 -125% RDN (187.5 kg N ha -1 ) replicated thrice in factorial randomized block design (FRBD). JGL-24423 variety was used for sowing with drum seeder having spacing of 20 × 8-10 cm after soaking in water for 24 hrs and incubating for 48 hrs. The recommended fertilizer dose of 60 kg P 2 O 5 was applied to all the plots as basal dose in the form of single super phosphate and 40 kg ha -1 K 2 O in two equal splits viz., as basal at sowing and at panicle initiation stage in the form of muriate of potash. Nitrogen was applied in the form of urea as per treatments in three equal splits viz., as basal dose, tillering and panicle initiation stage. At 3 DAS, pre-emergence and at 2-3 leaf stage of weeds, post emergence herbicides were applied, while mechanical weeding was done at 25 and 50 DAS with conoweeder. Nitrogen content in plant and weed samples was estimated by the modified Kjeldahl method using an automatic Kelplus distillation unit after digestion with concentrated H₂SO₄ and H₂O₂ as described by Jackson (1973) [5] and Piper (1966) [12] . Phosphorus and potassium contents were estimated after digesting the samples with a di-acid mixture of HNO₃ and HClO₄ (9:4 ratio). Phosphorus content was determined using a spectrophotometer at 420 nm by the Vanado-Molybdo phosphoric yellow colour method, while potassium content was determined using a flame photometer following the procedures described by Piper (1966) and Jackson (1973), respectively. Nutrient uptake of N, P and K by crop and weeds at different growth stages was calculated by multiplying nutrient content (%) with respective dry matter production and expressed in kg ha⁻¹ using the following formula: Data was analyzed statistically applying analysis of variance technique for FRBD design. (Gomez and Gomez 1984) [3] . Statistically significance was tested by F-value at 0.05% level of probability and critical difference was worked out where ever the effect were significant. Treatment differences that were nonsignificant were denoted as NS.

Results and Discussion

Nutrient removal by weeds Nutrient removal by weeds increased progressively from tillering to harvest and was significantly influenced by weed management practices and nitrogen levels The interaction effect between weed management practices and nitrogen levels was non-significant for phosphorus and potassium removal at all stages, but significant for nitrogen removal at tillering stage (Table 1). Among weed management practices, pretilachlor 6% + pyrazosulfuron-ethyl 0.15% GR @ 615 g ha⁻¹ as PE followed by mechanical weeding at 25 and 50 DAS (W 4 ) recorded the lowest N, P, and K removal by weeds and remained on par with pretilachlor 6% + pyrazosulfuron-ethyl 0.15% GR @ 615 g ha⁻¹ as PE followed by penoxsulam 1.02% + cyhalofop-butyl 5.1% OD @ 120 g ha⁻¹ as POE (W 2 ), whereas the unweeded treatment (W 1 ) recorded the highest nutrient removal. Among nitrogen levels, application of 125% RDN (N 4 ) resulted in maximum nutrient removal by weeds, while the control treatment (N 1 ) recorded the minimum removal. The interaction effect revealed that W 1 N 4 recorded the highest removal, whereas W 4 N 1 recorded the lowest (Table 2). Lower nutrient removal by weeds in weeded plots might be due to effective control of weeds during critical period which resulted in lesser weed dry matter production and lower NPK removal. Higher dry matter production and higher NPK removal by weeds in unweeded due to non adoption of weed control measures. Similar findings were reported by Gupta and Tomar (2019) [4] and Venkatesh (2020) [19] . Higher nutrient removal in 125% RDN treatment was due to higher weed dry matter. Lower removal was in no nitrogen plot, which revealed that the lower levels of nitrogen did not encourage weed growth and dry matter production. Similar results were reported by Subramanian and Martin (2007) [18] .

Nutrient Uptake by Crop

Nutrient uptake by crop increased progressively from tillering to harvest and was significantly influenced by weed management practices and nitrogen levels. Interaction effect was significant for nitrogen uptake at tillering, panicle initiation, flowering and grain stages, whereas it was non-significant for phosphorus and potassium uptake (Table 3). Among weed management practices, pretilachlor 6% + pyrazosulfuron-ethyl 0.15% GR @ 615 g ha -1 as PE followed by mechanical weeding at 25 and 50 DAS (W 4 ) recorded significantly higher N, P, and K uptakes by crop and remained comparable with pretilachlor 6% + pyrazosulfuron-ethyl 0.15% GR @ 615 g ha -1 as PE followed by penoxsulam 1.02% + cyhalofop-butyl 5.1% OD @ 120 g ha⁻¹ as POE (W 2 ), while the unweeded treatment (W 1 ) recorded the lowest uptake Among nitrogen levels, application of 125% RDN recorded maximum nutrient uptake and remained on par with 100% RDN, whereas the control treatment recorded the minimum uptake. The interaction effect revealed that W 4 N 4 recorded the highest nitrogen uptake, while W 1 N 1 recorded the lowest (Table 4 and5). Higher nutrient uptake under effective weed management and higher nitrogen levels might be attributed to reduced cropweed competition, improved nutrient availability, enhanced root growth, higher dry matter production, and better utilization of applied nutrients by the crop. Similar findings were reported by Reddy and Ameena (2021) [16] , Devi et al. (2012) [2] , Nayak et al. (2015) [11] and Kumar et al. (2016) [6] .

Conclusion

Application of pretilachlor 6% + pyrazosulfuron-ethyl 0.15% GR as PE followed by mechanical weeding at 25 and 50 DAS, or penoxsulam 1.02% + cyhalofop butyl 5.1% OD at 120 g ha⁻¹ as POE, enhanced nutrient uptake by crop and reduced nutrient removal by weeds. Higher nitrogen level (125% RDN) increased nutrient uptake by both crop and weeds. Overall, effective weed management with optimum nitrogen application improved nutrient use efficiency and crop performance in drum-seeded rice.

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