Weed management and nitrogen in enhancing productivity of direct seeded rice: A review

Introduction

Direct-seeded rice (DSR) is gaining popularity worldwide as a viable alternative to traditional puddled transplanted rice due to its water, energy, and labour savings, and its greater sustainability. But the uptake of DSR is limited by two closely related management issues: the ubiquitous weed problem and efficient nitrogen (N) use. In DSR, rice and weeds germinate almost at the same time in dry conditions, as opposed to puddled transplanted rice, where rice gets a "head-start," and many weed species are controlled in the flooded environment (Sandhu et al., 2021; Kumar et al., 2021) [63,28] . This change in planting practice leads to more complex weed communities (grasses, sedges, and broadleaf weeds in two or more flushes), which can inflict much greater losses in DSR than in puddled transplanted rice if not managed properly (Sandhu et al., 2021; Kumar et al., 2021) [63,28] . On the other hand, DSR is being introduced in areas facing groundwater scarcity, increasing production costs, and environmental concerns associated with greenhouse gas emissions and nutrient losses, so DSR's success depends on the management of nitrogen and nitrogen use efficiency (NUE) (Little et al., 2021; Govindasamy et al., 2023) [34,19] . Nitrogen is a vital nutrient for rice, but it is also the most susceptible to losses; low NUE not only affects profitability but can also cause water and air pollution, and can promote weed growth and competitiveness, further exacerbating the yield gap (Marzouk et al., Sabour, Sharma et al., (2007) [66] identified broad-leaved weeds (Commelina benghalensis, Caesulia axillaris, Eclipta prostrata, Euphorbia hirta, Portulaca oleracea, Trianthema portulacastrum, Lindernia spp.), sedges (C. rotundus, C. iria), and grasses (Phyllanthus niruri, E. crusgalli, Lindernia viscosa, Amaranthus viridis) Mishra and Singh found them to be Echinochloa colonum, Phyllanthus spp., Commelina communis, Cyperus iria, Alternanthera sessilis, Dinebra retroflexa, Physalis minimum, and Caesulia axillaris as the main weeds associated with dry direct-seeded rice (DSR) in Jabalpur, Madhya Pradesh. Yadav et al. (2008) [75] identified E. colonum, Cyperus rotundus, Cynodon dactylon, Commelina diffusa, and Ammania baccifera as the most predominant species in Kumarganj (U.P.). Anwar et al. (2011) [5] conducted a study that found 20 species of weeds in 10 families at Universiti Putra in Malaysia. The E. colonum, Physalis heterophylla, Cleome rutidosperma, C. iria, and C. rotundus were the major weeds constituting 31% of the weed community, with the broad leaf weeds representing 49 percent of the total dry matter. Naresh et al. (2011) [47] state that the weeds are uncontrolled and may lead to losses in production of 6592. Naseeruddin and Subramanyam (2013) [49] also identified broad-leaf weeds (Eclipta alba 6.5%), grasses (E. colonum 10.1%), and sedges (Cyperus difformis 40, C. iria 21.4, C. rotundus 12.22) as the predominant weeds in the loamy sands with the rice that has been sown with drum seeds. Raj et al. (2013) [55] showed that weeds in DSR that were not grass resulted in a 72 percent decrease in yield. Kaur and Singh (2015) [23][24] found the losses between 35 and 100 percent in resource conservation technologies (RCTs) systems, which have no weed management. According to Ramesh et al. (2015) [57] , effective pesticide or hand-weeding treatments had a significant positive impact on yields by reducing the content of weeds, dry weight, and competition. Saravanane et al. (2016) [65] discovered that uncontrolled aerobic rice in coastal environments lost 86.3 percent of its output in Puducherry, India.

Losses Caused by Weeds in Rice

Critical Period of Crop-Weed Competition in Direct-Seeded Rice

Weed emergence interferes with yield loss patterns as Gibson et al. (2001) [18] demonstrated when they retarded the development of Echinochloa phyllopogon by 30 days after rice seeding. Some experiments have established CPWC of some rice establishment methods, such as upland DSR, the first 30 DAS (Ladu and Singh, 2006) [33] ; dry-DSR, 15-45 DAS (Rao and Nagamani, 2007) [58][59] ; wet-DSR, 15-60 DAS (Mukherjee et al., 2011) [43] ; and drilling DSR, up to 45 DAS (Naidu and B Maintaining crop free of weeds during such periods is also critical in achieving yield outcomes that would be equal to the outcomes of the totally weed-free places. According to research, weed competition between 15 and 30 DAS has a significant impact on grain production, whereas it is found that weeds after the initial 15 DAS have minimal impact on the yield. Weed infestation of a season can cause an output hit by 93.6 percent (Ladu and Singh, 2006) [33] . Outsourcing in control weeds reduced output in wet and dry DSR 61 and 96 percent, respectively (Maity and Mukherjee, 2008) [39] . Recommended by Juraimi et al. (2010) [22] are the DSR weed-free situations of 2 to 71 DAS within saturated conditions and 15 to 73 DAS within flooded situations. Mubeena et al. (2014) [42] observed that paying attention to the weed control within 15-30 DAS reduces yield loss in DSR and effectively reduces the weed dry weight.

Nitrogen Management on Growth and Yield of Direct-Seeded Rice

Research conducted by Alagesan and Babu (2011) [3] and Chaudhary et al. (2011) [10] showed that four equal divisions at the seedling, active tillering, panicle initiation, and blooming stages performed better in developing growth, yield characteristics, and grain production compared to three-split plans. Mahajan et al. (2011) [37] have reported the highest output of grain (7.55 to 7.76 t ha -1 ) at 150 kg N ha -1 applied in four applications with no baseline nitrogen. According to Yoseftabar (2013) [76] , split nitrogen applications enhanced pre-anthesis dry matter, LAI, crop growth rate, the panicle-bearing tillers, kernels per panicle, 1000-grain weight, straw and grain yield, and harvest index, and maximized the spikelet fertility and reduced sterility. Kumawat et al. (2017) [32] also discovered that the highest combined grain production in DSR at IARI, New Delhi, was achieved when a quarter of the recommended amount of nitrogen was applied at baseline, week 2, week 5, and week 9 after planting.

Nitrogen Management on Weed Dynamics in Direct-Seeded Rice

The use of nitrogen has effects on the weed biomass and population, besides crop growth and production in direct-seeded rice (DSR). Nair et al. (2002) [45] examined the effects of different nitrogen treatments and methods of managing weeds on the dynamics of the weed in DSR (cv. Mahamaya). Besides six weed management methods, including mechanical weeding, manual weeding, submergence, anilofos, 2,4-D, and an unweeded control, the treatments included four schedules of N, namely 0:25:40:35, 25:0:40:35, 50:0:25:25, and 0:40:30:30 at 0, 20, 35, and 60 DAS. The results indicated that split nitrogen application had a capacity to influence the population of weeds, where the lowest population and dry matter of wheat was found in 0:25:40:35% N schedule at harvest. Chaudhary et al. (2011) [10] found that four equivalent splits (¼ at early tillering, active tillering, panicle initiation, and blooming) lowered the growth of the weed. N-scheduling with ½ at sowing + 1/4 at tillering + 1/4 at panicle initiation raised weed density and dry weight. In directseeded rice, Kumar et al. (2015) [30] discovered that four splits of nitrogen treatments (¼ at 2 WS, 4 WS, 6 WS, and 8 WS) resulted in a single optimum total weed density and dry weight, highest weed control efficiency, least index of weed, and maximum crop growth and crop yield.

Nitrogen Management on Nutrient Uptake and Removal

Besides the crop development, the nutrient absorption and the competition with weeds in the direct-seeded rice (DSR) require nitrogen control. Sharma et al. (2007) [66] observed that the crop gained a greater amount of dry matter and more nitrogen when two-thirds of the nitrogen dose was administered at 20 DAS, followed by one-fourth and one-fourth at tillering and panicle initiation, respectively. These findings were comparable to the plots that were subjected to butachlor at 1.5kg/ha, followed by hand weed at 30 DAS. This implies that proper scheduling of N has the potential to improve nutrient uptake besides controlling weeds. According to Raj et al. (2014) [54] , the highest amounts of grain yield were recorded at 3752 and 3872 kg ha -1 in the first and second year, respectively, when urea was divided into four equal doses between 5 -10 and 6065 DAE, which reduced the amount of nitrogen lost and maximized growth and production. Singh et al. (2015) [69] have found that 150 kg N ha in four splits (base, active tillering, panicle initiation, and flowering) at the N.E. increased nitrogen uptake (NPK) in DSR. Borlaug Crop Research Centre of Pantnagar. The effectiveness of N splits in DSR was also found by Rehman et al. (2016) [61] , who also ensured that split application of 1/2 basal + 1/4 tillering + 1/4 anthesis and 1/3 basal + 1/3 tillering + 1/3 anthesis produced the highest overall nitrogen uptake, which was comparable to two-Split application.

Weed Management Practices on Crop and Weed

Even though it is impossible to kill the weeds completely, an effective weed management program must ensure that the levels of weeds remain below the economic level and prevent the weed flora from evolving into the more injurious species. Weed management has been one of the main inputs in rice production since weeding occupies a significant portion of labor in general.

The control of weeds has to be done within the initial 30 to 40 days of sowing, as the weeds pose the greatest threat to the production in the early stages of crop growth, as they compete the most in the initial stages. The management of weeds in rice may take three methods: chemical, mechanical, and cultural. Weed management is of particular concern to direct-seeded rice (DSR) because the soil is exposed at the initial stage of growth.

Before sowing

Prevents the introduction of weed seeds into the field IRRI (n.d.); Chauhan (2012) [11] 2

Cleaning field bunds and irrigation channels Preventive Echinochloa spp., Cyperus spp., Fimbristylis spp.

Before sowing and during the crop season

Prevents the movement of weed seeds from field margins IRRI (n.d.) Allows the first weed flush to emerge and be destroyed before crop establishment IRRI (n.d.); Chauhan (2012) [11] ; Kumar et al.

(2020) [31] 5 Puddling Cultural

Many upland grassy weeds and some sedges

Reduces weed emergence under puddled lowland conditions

Rao et al. (2007) [58][59] ; IRRI (n.d.) [11] ; Kumar et al.

(2020) [31] 10 Early canopy closure Cultural Annual grasses and broadleaf 20-40 DAS Suppresses late weed emergence through shading Chauhan (2012) [11] weeds 11

Crop rotation Cultural

Weedy rice, sedges, grassy weeds

Seasonal / yearly

Breaks the weed life cycle and reduces the weed seed bank Rao et al. (2007) [58][59] ; Kumar et al.

(2020) [31] 12 Brown manuring with Sesbania

Cultural / Biological

Echinochloa spp., Cyperus difformis, broadleaf weeds 20-30 DAS in DSR

Smothering and allelopathic suppression of weeds

Kumar et al. (2020) [31] ; Chauhan (2012) [11] 13 [41] 19 Hand roguing of weedy rice

Mechanical / Preventive

Weedy rice (Oryza sativa f. spontanea)

Before flowering

Prevents seed set and spread of weedy rice Kumar et al. (2020) [31] ; IRRI (2018) [21] 20 [31] ; Mir et al.

(2024) [41] 34 Herbicide rotation Resistance management

Herbicide-resistant weeds and weedy rice

Across seasons Prevents herbicide resistance build-up Kumar et al. (2020) [31] ; IRRI (2018) [21] [31] ; Rao et al. (2007) [58][59] ; IRRI (n.d.)

39 Zero weed seed rain approach Preventive / IWM All seedproducing weeds Before flowering and harvest Prevents replenishment of the weed seed bank Kumar et al. (2020) [31] ; Chauhan (2012) [11] 40 [41] ; Kumar et al.

(2020) [31] [58][59] ; Kumar et al.

(2020) [31] 2 Jungle rice Echinochloa colona Grass DSR and upland rice Rao et al. (2007) [58][59] ; Kumar et al.

(2020) [31] [58][59] ; Kumar et al.

(2020) [31] 7 [58][59] ; Kumar et al.

(2020) [31] 10 [58][59] 15 Weedy rice / red rice Oryza sativa f. spontanea Special weed Direct-seeded rice Kumar et al. (2020) [31] ; IRRI (2018) [21] Dry tillage, aerobic soil conditions, and methods such as alternating watering and drying promote the germination and growth of highly competitive weeds. In addition, herbicides, as well as all other weed management options, are not very effective in dry-seeded systems because of the limited water management. In the case of the puddled transplanted rice, manual weeding was the most popular in the past. Nevertheless, such a solution is not as viable and often unprofitable because of the high price of labor and the absence of personnel at the time of a vital wedding. It is under these circumstances that farmers are turning towards chemical weed management as an effective alternative in a bid to replace them in a prompt manner.

Manual Weeding

Manual weeding is one of the most effective methods to deal with the weeds in direct-seeded rice (DSR). Subash and Solanki (2003) reported that a single-hand weeding enhanced the ear bearing tillers, but two-hand weedings enhanced the ear length, the number of grains per ear, the weight of grain, the test weight, the harvest index, and the straw yield. Comparative with herbicides application at sequential stages: Two hand weedings of 20 40 DAS reduced the weed density and dry weight, enhanced the weed control efficiency, and yield and yield components, as found in the studies by Rao et al. (2008) [60] , Sangeetha et al. (2009) [64] , Brar and Buller (2012) [8] , Murthy et al. (2012) [44] , and Naseeruddin and Subramanyam (2013) [49] .

Herbicide Application

Manual and cultural methods of weed control have been supplemented by herbicide-based chemical control as an important tool in rice agriculture. Herbicides can be used to overcome the shortage of labor, increased labor costs, and the inappropriate availability at the right time. Herbicides are also an effective, economical, and efficient control method of weeds, once the appropriate concentration and stage of crop development are used. Chemical weed control is particularly useful in intensive agricultural areas, where timely manual weeding is prohibited by shortages of manpower and financial constraints. Nonetheless, since it is dangerous when used incorrectly and leads to phytotoxicity and negative effects on the development of crops, it is of utmost importance to pay close attention to the dose and time used.

Pendimethalin

Pendimethalin is a selective pre-emergence herbicide that is effective against most of the annual grassland weeds as well as some broad-leaf weed species. It operates by inhibiting microtubule formation, perturbing cell division, and disrupting microfibrils. It is, however, less productive in the resistance to sedges and is primarily effective against those weeds that are just emerging. Bahar and Singh (2004) [6] realized that 1.0 kg/ha at 2 DAS gave ideal control of Echinochloa colonum, Setaria glauca, and Dactyloctenium aegyptium, hence their maximum grain yield. In comparison, risking all the other combinations of herbicides and manual weeding, pendimethalin at 1.0 kg/ha, then hand weeding at 30 DAS decreased the growth of the weed plants and increased the production, as reported by Rao et al.

Oxadiargyl

Gitsopoulos and Williams (2004) conducted glasshouse pot experiments to determine the selectivity of another recently developed herbicide, oxadiargyl, on direct-seeded rice under aerobic and anaerobic conditions. They found that wet-seeded (anaerobic) rice was more resistant to oxadiargyl compared to dry-seeded (aerobic) rice. The efficiency of the herbicide on Echinochloa crusgalli (L.) was also enhanced when anaerobic conditions were used. These findings imply that pre-sowing treatment, followed by subsequent flooding, would reduce the selectivity of oxadiargyl in wet-sown rice and that it is more active in flood conditions. Chauhan and Johnson (2011) [12][13] also concluded that when aerobic soils were subjected to herbicides, rice exhibited worse symptoms of phytotoxicity as compared to saturated soils. Ramesh et al. (2015) [57] conducted an experiment in Bapatla, Agricultural College Farm, using direct-seeded rice, pyrazosulfuron-ethyl, and oxadiargyl as separate agents and in succession with azimsulfuron. When comparing the pyrazosulfuron-ethyl and penoxsulam, they discovered that the combination of oxadiargyl and penoxsulam gave the highest yield and the least density of the weed. The findings of Singh et al. (2016) [70] showed that one dose of preemergence (PRE) of oxadiargyl or one dose of post-emergence (POST) of bispyribacsodium reduced the weed density by 27-61 percent and resulted in 16 and 11 broadleaf weeds per m2, respectively, as compared to untreated plots. Comparatively, a greater reduction of 64-82 percent in the density of weeds was achieved through repeated PRE and POST treatments with herbicides.

Bispyribac

Qiang et al. (2000) [53] have indicated that bispyribac-sodium has moderate control activities on Leptochloa chinensis, and it has good control properties towards grasses (Poaceae), sedges, as well as broadleaf weeds such as Echinochloa crusgalli, Paspalum distichum, and Alternanthera philoxeroides. Bispyribac-sodium 0.04 kg ha -1 inhibited a broad range of rice weeds when sprayed during the third or fourth unfolded leaf stage and at the tillering stage (Risi et al., 2004). The herbicide raised the productivity, and it was not phytotoxic to rice. It has an excellent ecotoxicological physiology that qualifies it to be used in rice cultivation, which acts by inhibiting the formation of branched amino acids. Ranjit and Suwanketnikom (2005) found that the use of mechanical or physical weed management methods in combination with bispyribac-sodium or anilofos led to promising grain production in dry direct-seeded rice. Contrary to bispyribac-sodium alone, Damalas et al. (2008) [16] observed that it reduced its efficacy on Echinochloa oryzoides and Echinochloa phylogopogo with the use of carbaryl or dichlorvos, but increased its efficacy with diazinon. Bispyribacsodium and ethoxysulfuron, respectively, according to Hussain et al. (2008) [20] , give better control at 90.5 and 87.19 with the two weeds, respectively. Yadav et al. (2008) [75] found that application of bispyribac on the 15th or 25th day after transplanting (DAT) was more effective in managing grassy weeds; meanwhile, bispyribac application on 15 DAT was more effective in managing sedges and wider-leaf weeds. The increase in grain production of the 25 g ha -1 applied at 15 or 25 DAT over weedy checks was 174-199% and 37-41% in 2006 and 2007, respectively. Wheat harvests did not have any phytotoxicity or lasting effects.

Mahajan and Timsina (2011) [37] performed a study to understand the nitrogen rates and the weed control methods, and found that either hand-weeding or using herbicides like pendimethalin + bispyribac-sodium enhanced the grain yield, water productivity, and profitability of the directseeding rice. When they managed the weeds so that the nitrogen levels went up to 150 kg/ha, then there was a great increase in yields. Like ethoxysulfuron ethyl and penoxsulam, bispyribac-sodium reduced the density of the weed by 75 percent (Khaliq et al., 2013) [25] . The second-best weed control was bispyribac-sodium with an inhibition rate of 80%, and hand weeding reduced the weed biomass by nearly 90%. Kumar et al. (2013) [29] found that bispyribac-sodium (2030 g ha -1) was effective in controlling Echinochloa colona. Cyclophopbutyl/butachlor deviating to metsulfuron-methyl was the same in causing control of Cyperus benghalensis as was bispyribacsodium. The number of Cyperus species was also significantly reduced up to 60 DAT. Bispyribac-sodium reduced the number of weeds and biomass, which was statistically similar to that of treatments at 20 and 25 g ha -1. Height of plant, length of panicle, and tillers and spikelets per panicle were positively associated with rice grain yield, whereas biomass and weed counts were negatively associated with it. It was expected that the production of grain would reduce by 15.3 kg ha -1 divided by m 2 of the additional weeds before harvest. No phytotoxicity or any long-term effects on the frequent harvests of wheat were observed. Prakash et al. (2013) [51] found that all the treatments reduced the population of weeds significantly and improved yield in their analysis of new herbicides on transplanted rice. Despite being very expensive and time-consuming, manual hand weeding yielded the best control (6482%). Maximum control of weeds (5875) was realized with the use of bispyribac-sodium at 50 g ha -1, which was similar to the lower doses, 25 and 35 g ha -1, at 1520 DAT. Veeraputhiran and Balasubramanian (2013) [72] evaluated bispyribac-sodium on rice transplants ASD 16 and ADT 37. They found that 25 g ha -1 was equally effective in the inhibition of weeds and increasing the grain yield as compared to the higher doses (35 and 50 g ha -1). In 2010 and 2011, the highest yields were 6.84 and 6.51 t ha -1, respectively. These yields were much superior to butachlor sprays and were similar to increased dosages, hand weeding, and weed-free treatments.

Pyrazosulfuron

Yadav et al. (2011) [74] observed that the herbicides pyrazosulfuron, azimsulfuron, and ethoxysulfuron were more effective than the herbicides pendimethylan and oxadiargyl in direct-seeded rice. Ramesh et al. (2015) [57] conducted their experiments with pyrazosulfuron-ethyl and oxadiargyl in the Agricultural College Farm in Bapatla, either separately or in combination with azimsulfuron. As in direct-seeded rice, where pyrazosulfuron-ethyl was used followed by penoxsulam, they found that oxadiargyl was used followed by penoxsulam, resulting in the highest yield and least weed density. Shukla et al. (2016) [67] found that the most effective treatment of preemergence was the application of pyrazosulfuron at a rate of 20 g ha -1 with a single hand weeding of the crops at 40 DAT/DAS. This dramatically decreased the population of the grass weeds as compared to all other tank-mix herbicide treatments, even a mixture of fenoxaprop and ethoxysulfuron 18 DAT/DAS in direct-seeded rice.

Sequential Herbicide Application

A combination of herbicides and the consecutive application of pre-and post-emergent herbicides has been identified to effectively control weeds in dry direct-seeded rice (DSR), thereby enhancing production and giving economic benefits. Pre-emergence herbicides such as quinolarc, benthiocarb, and pendimethalin inhibit the growth of annual grasses and broadleaf weeds due to their persistent nature in the soil. These are followed by the use of post-emergence herbicides used to control weed flushes. The extent of grain production lost due to the lack of the post-emergence treatment may be 9% to 60% (Cauley et al., 2005) [9] . As an example, pre-emergence pendimethylan (0.75 kg ha -1 ) and bispyribac sodium (0.025 kg ha -1 ) at 20 DAS gave an equal effectiveness in weed control as the manual weeding (Anonymous, 2007). It is because of the enormous range of species of the weed present in DSR fields that single applications of a herbicide are ineffective and less cost-effective (Khaliq et al., 2011) [26] . Since a majority of the herbicides attack grassy, sedges, or broadleaf weeds but not all of them, the action is rarely effective enough to provide a high level of control as it does in other upland cereals (Ahmed and Bhuiyan, 2010) [1] . Mahajan and Chauhan (2013) [36] confirmed that either pendimethylan-sulfuron then azimsulfuron or pendimethylansulfuron then bispyribac-sodium at 15 DAS effectively reduced the weed biomass in DSR.

Tank Mixture Herbicide Application

Direct-seeded rice (DSR) weed control requires simultaneous application of herbicides with multiple modes of action to get a broad-spectrum weed control and avoid herbicide resistance. In order to manage the various weed flora, there is a need to identify cost-effective and efficient herbicide combinations, which a small number of researchers have examined this approach in DSR. Single pre or post-emergence herbicides are difficult to use to manage weeds in DSR due to complex weed flora (Mahajan et al., 2011) [37] . In comparison to using a single herbicide, tank mixing, or concurrent application of herbicides, or sequential application, which is the combination of herbicides, does tend to improve the weed control (Mahajan and Timsina, 2011). Mahajan and Chauhan (2013) [36] also supported the effectiveness of consecutive pre-and postemergence herbicide application as compared to individual herbicide application. Bispyribacsodium + azimsulfuron is an effective tank mixture that can be used in cases of co-existence of broadleaf and grassy types of weeds. Azimsulfuron enhances control spectrum by inducing bispyribac, which alone is unable to control sedges and broadleaf weeds (Walia et al., 2008) [73] . In fact, the weed biomass was decreased at 45 DAS by 82-91 when the weed was treated with pendimethalin as a pre-emergence herbicide and bispyribac sodium and azimsulfuron as postemergence treatments.

Weed Management Practices on Nitrogen Removal by Weeds and Nitrogen Uptake by Crops

It has been demonstrated in the literature that effective weed management strategies are necessary to reduce the loss of nutrients by the weeds and enhance the uptake of the nutrients by the crop, which boosts productivity in direct-seeded rice in general. Brar and Bhullar (2013) [8] report that pendimethalin and bispyribac eliminated significantly more nitrogen, phosphorus, and potassium when sprayed compared to when three-hand weedings were done. Weed biomass accumulation, on the other hand, was related to the nutrient removal by the weed, but crop dry matter accumulation and crop grain yield were directly related to crop nutrient uptake. Amazingly, the crop took up greater nitrogen in the three-hand herbicide treatment in comparison with the sequential application of herbicides. Narolia et al. (2014) [48] found that the use of preemergence pendimethylan (1.0 kg/ha) and bispyribac sodium (35 g/ha) yielded the most suitable growth and yield properties, enhanced weed control efficacy, and reduced weed uptake of NPK at 45 DAS and harvest.

Economics of Weed Management in Direct-Seeded Rice

One of the greatest contributors to the actual use of the methods of weed management is the economic feasibility of the method. Though hand weeding is an excellent method of minimizing the competition of weeds and achieving higher yields, it is impractical in the case of many rice farmers because of the high price of labor and shortage of manpower during the peak season of agricultural activities. [46] . Meena (2010) discovered that application of nitrogen in three splits (40:40:40) resulted in higher net returns which were comparable with the other schedules and significantly higher than the two-split applications; Upasani et al. (2010) [71] found that untreated plots produced negative net returns in direct seeded rice under weed competition (when compared to other schedules), and Chaudhary et al. (2011) [10] found that untreated plots produced the maximum net returns (16, 145/ha) Bhurer et al., (2013) [7] demonstrated that economic losses in direct-seeded rice, and they estimated that the lowest net returns per rupee invested are in untreated plots (0.70 in 2010 and 0.05 in 2011).

Naseeruddin and Subramanyam (2013) [49] identified the preemergence application of oxadiargyl and azimsulfuron as the most beneficial-cost ratio of 3.30, which is far better than other weed management methods in the drum-seeded rice fields. Kaur and Singh (2015) [23][24] found that the untreated plots and the treatments of single applications of herbicides were found to give negative returns, whereas pendimethalin and bispyribac were found to give the highest net returns and B: C ratio when applied sequentially. Mahajan and Chauhan (2015) [35] established that tank mix application of azimsulfuron plus bispyribac plus fenoxaprop yielded the greatest incremental net profit and B: C ratio when compared to sequential or single herbicide treatment. The lowest profits were made in one application of herbicide. Pinjari et al. (2016) [50] concluded that because competition with weeds caused negative changes in crop development and yields over the course of the season, untreated plots were characterized by the lowest B: C ratio and negative net returns. Rehman et al.

(2016) [61] found that certain nitrogen treatment regimes, including ½ basal + 1/4 tillering + 1/4 anthesis and 1/3 basal + 1/3 tillering + 1/3 anthesis, were the most practical as they yielded the highest net returns and B: C ratios due to higher grain yields. Saravanane et al. (2016) [65] found in directseeded rice that the B: C ratio (0.40) and net return (-11,180/ha) were lowest in untreated plots compared to herbicide treatments. Singh et al. (2016) [70] found that pendimethalin, bispyribac sodium, and azimsulfuron were most effective as the successive tank mix application in terms of net returns and B: C ratio, in direct-seeded rice at IRRI and Haryana. These were preceded by a succession of pendimethalin application and bispyribac sodium application.

Conclusion

The management of nitrogen and weeds is significant to improve the productivity of directseeded rice (Oryza sativa L.). When applied properly, nitrogen enhances proper nutrition of the crop, thus leading to healthy growth, tillering, and filling of the grain. Nevertheless, the competition between weeds usually compromises the efficiency of nitrogen use by depleting the available nutrients, decreasing the light interception, and making crops develop unproductively. Combined weed management techniques, such as the application of pre and post-emergence herbicides coupled with manual or mechanical weeding, hugely decrease the weed density and biomass and, as such, reduce nutrient losses. Balanced, timely, and proper application of nitrogen fertilization and weed management enhances nutrient uptake in crops, growth of dry matter, and eventually yields. Additionally, nutrient management can be done on a sitespecific basis based on factors of soil fertility, water availability, and the crop stage to enhance the efficiency of nitrogen use without posing too much environmental risk that comes with over-fertilization. The use of these combined ways would not only increase yield but also help in the sustainable and resourceefficient production of rice. In conclusion, nitrogen and weed control are an essential part of direct-seeded rice farming, and their joint application is a major factor in the higher yield and food security.

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