Economic Assessment of Herbicide Use in Rice Under Different Establishment Methods in Northwest India

Abstract

Large weed infestation is a major problem in dry direct-seeded rice (DSR). Chemical weed control serves as a crucial component for integrated weed management in DSR. Over the last decade, herbicide use has increased from 42 to 55%, and the worldwide contamination of water resources and food by herbicides is a major health issue. In the present study, the use of herbicides in three different establishment methods of rice was examined with the objective to present and discuss the herbicide use pattern and cost of weed control. For this, a field-wide survey was conducted over an area of 165.4 ha in eight villages of the Tarn Taran District of Punjab, India. For two DSR methods, during the initial stage of crop growth, the weed infestation was reported to be less in moist fields sown with direct seeding (soil moisture in the field capacity stage) after pre-sowing irrigation (DSR-PSI). The herbicide use and cost of weed control under DSR-PSI conditions were similar to that of puddled transplanted rice, but were significantly lower than that of direct seeding in dry fields (rice seeds are sown in dry fields, and irrigation is applied immediately after sowing), i.e., DSR-IAS. Therefore, the DSR-PSI method of rice establishment can ensure minimum dependence on herbicides, as well as other benefits of direct seeding. Thus, there is a need to promote the DSR-PSI method over the DSR-IAS method among farmers in order to reduce herbicide use in DSR and ensure environmental safety.

1. Introduction

Rice is a major summer crop of Northwest India that is grown extensively in the rice–wheat cropping system. Most farmers in the region are following the puddled transplanted rice (PTR) method of rice establishment, in which the 25–35-days-old nursery of rice is transplanted into a puddled field and irrigation water is kept ponded in the field continuously for the first 15 days in order to facilitate the establishment of the roots of rice seedlings. The puddled transplanting of rice is a water-guzzling cultivation method [1] and the huge requirement of water (3000–5000 litres per kilogram of rice production) puts pressure on groundwater tables. Furthermore, continuous increases in cultivation area over the last five decades have resulted in the overexploitation of underground water, which has led to a further decline in water tables in Northwest India [2]. The major concern regarding the cultivation and sustainability of this crop in this region is its high water requirement. Puddling helps to create anaerobic conditions in the field, which suppress the germination of weed seeds, which require aerobic environments. Furthermore, the PTR method of rice establishment is considered as a source of methane (CH₄) emission, which is a major culprit in relation to global warming and climate change, accounting for 10–20% of the global annual CH₄ emissions [3]. In addition to this, the PTR method also deteriorates the soil’s physical properties, thus adversely affecting the performance of succeeding crops in the field.

The direct seeding of rice can occur in one of two ways—dry direct-seeded rice (dry-DSR) and wet direct-seeded rice (wet-DSR), in which seeding is performed in unpuddled/aerobic and puddled fields, respectively [4]. Dry-DSR, hereafter referred to as DSR, is an alternate technology that can be used to transplant rice; this process is water-, labor-, and energy-efficient. The DSR method has the potential to improve the efficiency of water use and is an efficient and effective resource-conserving technology. In addition to this, the DSR method is a climate-resilient technology that results in lower emissions of greenhouse gases (GHGs), and provides better physical soil conditions for the succeeding crop [5,6,7]. A reduction of 25–30% in CH₄ emissions by shifting from PTR to DSR was reported by Joshi et al. [8].

The major problem faced by farmers adopting the DSR method is high weed infestation due to the aerobic conditions in the field throughout the crop season [9,10,11,12]. A yield loss of 30–80% or even complete crop failure of DSR due to weed competition was reported by Matloob et al. [13]. Weeds are the single largest biological constraint in the DSR method. Rao and Nagamani [9] reported 136 weed species relating to DSR in India. The success of DSR depends upon the effective management of diverse and competitive weed flora. After the continuous adoption of DSR technology in the field, the predominant weed species in rice fields such as Echinochloa crus-galli (L.) Beauv, E. colona (L.) Link, Cyperus iria L., and C. difformis L. have shifted towards Dactyloctenium aegyptium (L.) Willd., Leptochloa chinensis (L.) Nees., and the perennial sedge Cyperus rotundus L. [14]. In order to control these weeds, the DSR method requires the use of more herbicides or more hand weeding than the PTR method [15]. The DSR method is also known as “herbicidal farming” as weed management through chemicals is practical, remunerative, and effective in the DSR method [16]. To control complex weed flora under the DSR method, farmers follow the sequential application of pre- and post-emergence herbicides, depending upon the weed flora that is present in the fields.

Due to the increased weed pressure, there is a higher herbicide load in the DSR fields, which raises concern about environmental pollution and the contamination of groundwater. Bamal et al. [17] raised concern about the harmful effect of herbicides on ecosystems and non-target organisms due to their extensive use in agricultural fields. They further reported that many herbicides are not easily biodegradable and enter the environment/aquifers through agricultural runoff, contaminated groundwater, and water bodies. The risk of contamination in water bodies has increased due to their water solubility [18]. Over the past 10 years, herbicide use has increased from 42 to 55%, and the worldwide contamination of water and food by herbicides is a major health issue [17]. Therefore, there is a need to assess the herbicide use in DSR at farmers’ fields in order to create awareness of the need to minimize the use of herbicides.

There are two DSR methods that are followed by farmers in this region. In the first method, the rice seeds are sown in a dry field and irrigation is applied immediately after sowing (hereafter, this method is referred to as DSR-IAS). In the DSR-IAS method, there is no pre-sowing irrigation stage, and the seedbed is prepared for sowing by discing/cultivations followed by planking. In the second method, sowing is carried out in moist field conditions (soil moisture in the field capacity stage) after pre-sowing irrigation (hereafter, this method is referred to as DSR-PSI). In the DSR-PSI method, after pre-sowing irrigation, a seedbed with a sufficiently high but workable soil moisture is prepared by shallow cultivations followed by two to three plankings [19]. The first irrigation in the DSR-PSI method is delayed by up to a maximum of 21 days after sowing, depending upon the soil’s texture and the weather conditions. In addition to its water-saving properties, the DSR-PSI method also claims an advantage over the DSR-IAS method in terms of reduced weed competition and a lower requirement for herbicides [19,20]. The DSR-PSI method is popularly known as the tar-wattar method among the farmers in the region [19]. The weed flora and herbicide use pattern in both DSR methods vary from field to field. To establish these facts, a field-scale survey study was needed to assess the weed infestation in relation to the two methods of DSR and the herbicides used by farmers to control weeds. The outcome of this study may help to provide feedback to weed scientists regarding the weed problem in farming fields. Furthermore, the quantification of the cost of weed control under different methods of rice establishment will also help scientists to promote economically viable methods of rice establishment among farmers. Therefore, to quantify the patterns of herbicide use and the cost of weed control under different establishment methods of rice, a survey was conducted on an area of 165.4 ha in eight villages of the Tarn Taran District of Punjab, India. The objective of this study was to present and discuss the herbicide use pattern and cost of weed control under different establishment methods of rice and to identify the rice establishment method with the least dependence on herbicides. The information generated will help to formulate strategies to educate farmers to reduce herbicide dependency in DSR methods to ensure environmental safety.

2. Materials and Methods

A field survey was conducted from May to August 2024 in farmers’ field in the Tarn Taran District of Punjab state (India). Tarn Taran is one of the border districts that lies in the Northwest frontier of Indian Punjab. The district is bounded by the ‘Beas’ river on the Southeastern side, and is dominated by rice–wheat cropping systems. It has an average rainfall of 482.9 mm, and tube wells are the main source of irrigation. The productivity of rice crops is 6339 kg/ha, owing to assured irrigation, the use of improved and high-yielding varieties, good infrastructural support, agro-advisories by agri-experts, etc.

During the period of the experimental study (May–October 2024), the maximum and minimum temperatures ranged from 36 to 46 °C and 14 to 23 °C, respectively. June reported the warmest month with a temperature of 46 °C, whereas the lowest minimum temperature was observed in the month of October. The total rainfall received during the study period (May–October 2024) was about 404 mm, with highest rainfall (248.0 mm) being observed in August. During the summer of 2024, coarse rice was cultivated on about 1.17 lakh ha and basmati (an aromatic rice with a GI tag) was cultivated on an area of 0.72 lakh ha; the total net cultivable area in the district was 2.18 lakh ha. The direct seeding of rice was practiced on about 1150 ha during the summer of 2024, while the remaining area was subject to the PTR method. Out of the total 165.4 ha area surveyed in eight villages (52 locations), 50% of the area was sown using the DSR-IAS method, 26% with the DSR-PSI method, and 24% with the PTR method of rice establishment (Figure 1). Furthermore, soil occupied about 15, 40, and 45 per cent of the area, with coarse loamy, coarse loamy and fine loamy associations, and fine loamy soil types, respectively. In general, soils exhibited a slightly or moderately alkaline reaction, had a low-to-medium organic carbon status, and presented with a fairly good availability of P and a rich availability of K. The micronutrients, viz. Zn, Fe, and Mn, varied from low to medium, with the optimum availability relating to Cu [21].

Eight villages in the Tarn Taran District were selected for this study, in which the farmers are following either the DSR-PSI or DSR-IAS method of rice establishment, along with PTR. The agronomic practices followed by the farmers for the cultivation of rice under different methods of establishment are given in

Table 1. Agronomic practices followed by the farmers for rice under different methods of establishment.

S. No.	Input/Farm Operation	PTR	DSR-PSI	DSR-IAS
1.	Seed rate (kg/ha)	12.5	20	20
2.	Time of sowing/ Transplanting under PTR	10 June 2024 to 25 June 2024	10 May 2024 to 5 June 2024	10 May 2024 to 5 June 2024
3.	First irrigation	Transplanted in puddled field with ponded water	12 to 21 DAS	1 to 2 DAS
4.	Subsequent irrigations	Irrigation water kept ponded in field for first 20–30 days and afterwards irrigation was applied at 2–3 days interval	At 2–5 days interval	At 2–3 days interval
5.	Method of application of pre emergence herbicide	Broadcasted in standing water after mixing with sand	Sprayed with knap sack sprayer fitted with flat fan/flood jet nozzle	Sprayed with knap sack sprayer fitted with flat fan/flood jet nozzle
6.	Time of application of pre emergence herbicide	2–5 DAT	1–2 DAS	4–5 DAS
7.	Time of application of post emergence herbicide	30–40 DAT	30–50 DAS	30–60 DAS
8.	Dose of nitrogenous fertilizer (Urea; kg/ha)	280 to 400	350 to 450	350 to 450
9.	Time of application of Urea	In three splits between 10–50 DAT	In three splits between 10–70 DAS	In three splits between 10–70 DAS

PTR: Puddled Transplanted Rice; DSR-PSI: Direct Seeded Rice in moist fields; DSR-IAS: Direct Seeded Rice in dry fields; DAT: Days after transplanting; DAS: Days after sowing.

. Data were collected with respect to the major weed flora present in the field, as well as the weed control methods (i.e., hand weeding, pre-emergence/post-emergence herbicides applied, time of application of herbicide, etc.) employed by the farmer. For the collection of data, field visits were conducted and information was collected through interview with farmers as well as field inspections. The weed flora observed in each surveyed field was noted down from four random locations in each field with a quadrate of 1m² (

Table 2. Major weed flora observed in the surveyed fields.

Method of Rice Establishment	Weed Flora
	Grasses	Broadleaf	Sedges
DSR-PSI/DSR-IAS	Echinochloa crus-galli	Ludwigia parviflora	Cyperus rotundus
	Echinochloa colona	Trianthema monogyna	Cyperus iria
	Leptochloa chinensis	Eclipta alba	Scirpus roylei
	Dactyloctenium aegyptium	Digera arvensis
	Eleusine indica
PTR	Echinochloa crus-galli	Ludwigia parviflora	Cyperus iria
	Echinochloa colona	Hydrilla verticillata	Cyperus difformis
	Leptochloa chinensis	Eclipta alba	Scirpus roylei

PTR: Puddled Transplanted Rice; DSR-PSI: Direct Seeded Rice in moist fields; DSR-IAS: Direct Seeded Rice in dry fields.

). The list of herbicides used in the fields surveyed, along with their toxicity ratings, is presented in

Table 3. Toxicity rating of herbicides used in surveyed fields.

Name	Formulation	LD50, Acute, Oral, Rat (mg/kg)	LD50, Acute, Dermal, Rat (mg/kg)	Toxic Rating *
Bispyribac-sodium	10% SC	4111	>2250	IV
Chlorimuron ethyl	25% WP	>4102	>2000	IV
Cyhalofop-butyl	10% SC	>5000	>2000	IV
Ethoxysulfuron	15% WG	3270	>5000	IV
Fenoxaprop-p-ethyl	10% SC	304	>2000	III
Florpyrauxifen-benzyl	2.7% EC	>5000	--	IV
Imazethapyr	10% EC/SL	>5000	>2000	IV
Metsulfuron methyl	0.6% WG	>5000	>2000	IV
Paraquat dichloride	24% SL	150	235–500	I–II
Pendimethalin	30% EC	4050	>5000	IV
Penoxsulam	240 SC	>5000	--	IV
Pretilachlor	50% EC	6099	>3964	III
Pyrazosulfuron ethyl	10% WP	>5000	>2000	III
2,4-Dichlorophenoxy acetic acid	58% SL	375	>2000	II–III

* I—Extremely hazardous, II—Highly hazardous, III—Moderately hazardous, IV—Unlikely to pose any hazards. Sondhia [22], Choudhury et al. [23], APVMA [24].

. The cost of weed control under different methods of rice establishment was calculated based on the market price of labor or herbicides. The cost of weed control data was checked for normality using a Shapiro–Wilk test. The data were analyzed using the general linear model in IBM SPSS Statistics 22. Tukey’s Honestly Significant Difference (HSD) test was used as a post hoc test to compare the cost of weed control under different methods of rice establishment at an alpha level of 0.05. Tukey’s Honestly Significant Difference (HSD) test provides a more accurate and conservative assessment of pair-wise differences among group means.

3. Results

3.1. Weed Species Observed in the Fields

The major weed flora observed in the surveyed fields were Echinochloa crus-galli, Echinochloa colona, Leptochloa chinensis, Dactyloctenium aegyptium and Eleusine indica (L.) Gaertn. among grasses, while the broadleaf weeds that were reported included Ludwigia parviflora, Trianthema monogyna L., Hydrilla verticillata (L.) Royle, Eclipta alba (L.) Hassk., and Digera arvensis Forsk. Along with these, Cyperus iria, Cyperus difformis, Cyperus rotundus, and Scirpus roylei were observed among sedges (Table 2). Among these weed species, Dactyloctenium aegyptium, Eleusine indica, Trianthema monogyna, Digera arvensis, and Cyperus rotundus were not observed in PTR, while Hydrilla verticillata and Cyperus difformis were not observed under the DSR methods of rice establishment. Weed infestation was 50–90% less in PTR as compared to the DSR methods of establishment. Amongst two of the DSR establishment methods, weed infestation was 50–70% less in the DSR-PSI method compared to the DSR-IAS method during the initial stage of crop growth (up to 30 days).

3.2. Herbicide Use Pattern

In the DSR-PSI method, pre-emergence herbicides were not applied to 36% of the area, while pendimethalin was applied to 6% of the area; a tank-mix of pendimethalin + pyrazosulfuron ethyl was applied to 19% of the area; paraquat was applied to 19% of the area; and pretilachlor was applied to 20% of the area (Figure 2a). In the DSR-IAS method, pendimethalin was applied to 32% of the area; a tank-mix of pendimethalin + pyrazosulfuron ethyl was applied to 56% of the area; and no pre-emergence herbicides were applied to 12% of the area (Figure 2b). On the other hand, pretilachlor was applied to 67% of the area, while a tank-mix of pretilachlor + pyrazosulfuron ethyl was applied to 33% of the area in the PTR method of rice establishment (Figure 2c).

Furthermore, it was observed that for the post-emergence control of weeds, bispyribac sodium was applied to 24% of the area; fenoxaprop-p-ethyl was applied to 7% of the area; fluoropyrauxifen-benzyl + penoxsulam was applied to 11% of the area; bispyribac sodium + fenoxaprop-p-ethyl was applied to 34% of the area; and no post-emergence herbicides were applied to 24% of the area under the DSR-PSI method of rice establishment (Figure 3a). Under the DSR-IAS method of establishment, bispyribac sodium was applied to 23% of the area, bispyribac sodium followed by (fb) fenoxaprop-p-ethyl was applied to 25% of the area, bispyribac sodium fb fenoxaprop-p-ethyl fb hand weeding was carried out on 24% of the area, a bispyribac sodium fb fenoxaprop-p-ethyl fb premix of florpyrauxifen-benzyl plus cyhalofop-butyl was applied to 4% of the area, a bispyribac sodium fb fenoxaprop-p-ethyl fb premix of florpyrauxifen-benzyl plus cyhalofop-butyl and a premix of metsulfuron methyl plus chlorimuron ethyl were applied to 7% of the area, imazethapyr was used on 5% of the area, and hand weeding was performed on 12% of the area for the post-emergence control of weeds. Imazethapyr was used as a post-emergence treatment in fields where herbicide-tolerant rice cultivars (For example, Pusa Basmati 1979 and Pusa Basmati 1985) were cultivated (Figure 3b). Under the PTR method of establishment, bentazone was applied to 24% of the area, ethoxysulfuron was applied to 7% of the area, 2,4-D amine salt was applied to 6% of the area, metsulfuron was applied to 4% of the area, hand weeding was carried out on 11% of the area, and no hand weeding or post-emergence herbicides were applied to 48% of the area (Figure 3c). Under the DSR-PSI method, bispyribac sodium was the dominant herbicide, while pendimethalin and bispyribac sodium were dominant under the DSR-IAS method; additionally, pretilachlor was the dominant herbicide under the PTR method.

3.3. Economics of Weed Control

As concerns the economics of weed control, under the DSR-IAS method of establishment, it varies from USD 24 to 162 per hectare with an average cost of USD 89 per hectare (

Table 4. Cost of weed control under different methods of rice establishment.

Pre-Emergence Herbicide @ a.i. (g/ha)	Post-Emergence Herbicide @ a.i. (g/ha)	Area (%)	Cost of Weed Control (USD/ha)
DSR-IAS method of rice establishment
pendimethalin @ 750	hand weeding	8.0	63
pendimethalin @ 750	bispyribac @ 25 fb fenoxaprop-p-ethyl @ 67 fb hand weeding	24.2	113
pendimethalin @ 750 + pyrazosulfuron ethyl @ 15	bispyribac @ 25	22.8	63
pendimethalin @ 750 + pyrazosulfuron ethyl@ 15	bispyribac @ 25 fb fenoxaprop-p-ethyl @ 67	24.7	107
pendimethalin @ 750 + pyrazosulfuron ethyl @ 15	hand weeding	3.9	52
pendimethalin @ 750+ pyrazosulfuron ethyl @ 15	bispyribac @ 25 fb fenoxaprop-p-ethyl @ 67 fb florpyrauxifen-benzyl @ 26.63 + cyhalofop-butyl @ 133	4.4	162
--	bispyribac @ 25 fb fenoxaprop-p-ethyl @ 67 fb florpyrauxifen-benzyl @ 26.63 + cyhalofop-butyl @ 133 fb metsulfuron methyl @ 2 + chlorimuron @ 2	7.3	125
--	imazethaper @ 100	4.8	24
Average			89 b
DSR-PSI method of rice establishment
pendimethalin @ 750	florpyrauxifen-benzyl @ 16.38 + penoxsulam @ 26.25	6.6	92
pendimethalin @ 750+ pyrazosulfuron ethyl @ 15	Bispyribac @ 25 fb fenoxaprop-p-ethyl @ 67	18.9	95
paraquat @ 300	--	18.9	25
--	bispyribac @ 25	24.5	24
--	fenoxaprop-p-ethyl @ 67	6.6	44
--	florpyrauxifen-benzyl @ 16.38 + penoxsulam @ 26.25	4.7	58
pretilachlor @ 750	--	4.7	24
pretilachlor @ 750	bispyribac @ 25 fb fenoxaprop-p-ethyl @ 67	15.1	79
Average			55 a
PTR method of rice establishment
pretilachlor @ 750	--	15.84	24
pretilachlor @ 750	hand weeding	10.89	36
pretilachlor @ 750	bentazone @ 1200	23.76	64
pretilachlor @ 750	metsulfuron @ 15	3.96	53
pretilachlor @ 750	2,4-D (amine salt) @ 696	5.94	42
pretilachlor @ 750	ethoxysulfuron @ 18.75	6.93	52
pretilachlor @ 750+ pryzosulfuron ethyl @ 15	--	32.67	30
Average			43 a
p value			0.04

fb: followed by; PTR: Puddled Transplanted Rice; DSR-PSI: Direct Seeded Rice in moist fields; DSR-IAS: Direct Seeded Rice in dry fields; a.i.: active ingredient; Mean with different lower case letters differ significantly at probability level p.

). Under the DSR-PSI method of establishment, it varies from USD 24 to 95 per hectare with an average cost of USD 55 per hectare. Under the PTR method of establishment, it varies from USD 24 to 64 per hectare with an average value of USD 43 per hectare. The cost of weed control was minimal for PTR, statistically similar to that of the DSR-PSI method, and was lower than that of the DSR-IAS method.

4. Discussion

Rice is the foremost staple food crop of Northwest India. However, its high water requirement and energy use are the major concerns for its sustainable cultivation in the region. The DSR method is an alternative technology to transplanted rice, which is water-, labor-, and energy-efficient. Kaur et al. [25] observed that the area under DSR treatment may increase in South Asia. Chemical weed control serves as a crucial component for integrated weed management in the DSR method. Farmers prefer chemical weed control in rice due to the non-availability of labor for hand weeding at the proper stage of crop growth in larger farms, or due to high labor wages that lead to an increase in the cost of cultivation. Interestingly, more herbicides are being used in DSR than PTR systems. Nevertheless, the application of herbicides may result in negative effects on both the environment and human health, while also hastening the evolution of herbicide resistance in weeds.

Weed infestation was observed to be lower when using the PTR method of establishment, and weeds such as Dactyloctenium aegyptium, Eleusine indica, Trianthema monogyna, Digera arvensis, and Cyperus rotundus were not observed in PTR. The fact that these weeds require aerobic conditions and ponded water in PTR fields created anaerobic conditions that retarded the germination and growth of these particular weed species. On the other hand, Hydrilla verticillata and Cyperus difformis required submerged conditions for their establishment and were not observed under the DSR method because of the aerobic conditions in the fields. In the DSR method, the predominance of grasses like Leptochloa chinensis, Eragrostis spp., Dactyloctenium aegyptium, and Eleusine indica, as well as sedges like Cyperus rotundus, which were minor weeds in PTR in Northwestern India, was also reported by Yadav et al. [26].

Amongst the two methods of DSR, fewer weeds were observed under the DSR-PSI method than the DSR-IAS method of rice establishment. It was observed by farmers that the top 1.0 cm soil layer was dried due to plankings, and dry soil mulch was formed during the sowing of rice under the DSR-PSI method. In DSR fields, most weed seeds emerged from the top 1.0 cm soil depth. Therefore, the non-availability of moisture for the germination of weed seeds in the top 1.0 cm dry soil layer (due to the creation of dust/soil mulch) under the DSR-PSI method leads to a decreased weed infestation. Yaduraju et al. [20] also reported a reduced weed infestation in DSR fields sown after pre-sowing irrigation with a sufficiently high but workable soil moisture. Reduced and delayed weed emergence in DSR fields where sowing was performed in moist fields was also reported by Yadav et al. [26]. Therefore, due to the reduced weed infestation during the early stage of crop growth under the DSR-PSI method, no pre-emergence herbicides were used on 36% of the area. However, under the DSR-IAS method of rice establishment, the application of irrigation immediately after sowing provided moisture in the upper 1.0 cm soil zone, which facilitated the germination of the weed seeds present in the top layer of soil along with rice seedlings [20]. Ultimately, crops subjected to the DSR-IAS method were infested with more weeds, and pre-emergence herbicides were applied to 88% of the area. In the conventional PTR method, pre-emergence herbicides are primarily applied to keep the population of weeds in the field below the economic threshold level [25].

There are several challenges associated with the use of pre-emergence herbicides in DSR, including the limited application time window (0–5 days after sowing—DAS), the maintenance of critical moisture levels in the field, and the risk of toxicity to the main crop [27]. The use of post-emergence herbicides in sequence with pre-emergence herbicides depends upon the weed flora in the field, offering an alternate possibility. In DSR, weed management practices involving the application of pre-emergence herbicides followed by post-emergence herbicides were found to be effective in managing complex weed flora [28,29]. Furthermore, in areas where paraquat was used in the pre-emergence window under the DSR-PSI method, no post-emergence herbicides were used (Table 4). In these fields, some weeds started emerging before the sowing of rice and paraquat in the pre-emergence window. It was observed that farmers opted for post-emergence herbicides only where the crops were infested with weeds at 25–30 DAS. However, with a delay in the first irrigation of up to 21 DAS in DSR-PSI fields, the germination of weed seeds was suppressed. On the other hand, post-emergence herbicides were used and/or hand weeding was carried out on 100% of the area under the DSR-IAS method. Under this method of establishment, frequent irrigations after sowing facilitated weed emergence in the fields. Therefore, post-emergence herbicides were used or hand weeding was performed to control these flushes of weeds. Under the PTR method, post-emergence herbicides were not used and hand weeding was also not performed on 48% of the area, because the pond water in the field suppressed the germination of weed seeds at the later stages of crop growth. Only some sedges and broadleaf weeds were observed in 52% of the area, which were controlled by using herbicides/hand weeding. Therefore, the reduced use of herbicide under DSR-PSI fields than DSR-IAS fields helped to reduce the chemical load in DSR fields and was determined to be a more eco-friendly rice establishment method. Furthermore, dust mulch and delaying the first irrigation by 21 days after sowing helped in controlling weed emergence in the initial crop growth period. More integrated weed management options such as stale seed beds, crop rotation, brown manuring, etc., may help in reducing weed infestations in DSR production systems [4,10,12,13].

The cost of weed control was lower in PTR, as no post-emergence herbicides were used in 49% of the area, and only one post-emergence herbicide was used or hand weeding was conducted for the control of broadleaf weeds and sedges in 51% of the area (Table 4). Yaduraju et al. [20] also reported a cost of weed control in relation to PTR in the range of USD 24–30 per hectare, as compared to USD 30–47 per hectare under the DSR method. Amongst the DSR methods, DSR-PSI recorded a lower cost of weed control, which was statistically similar to that of PTR. Under the DSR-PSI method, only single pre- or post-emergence herbicides were used on 59% of the area (Table 4), leading to a lower cost of weed control. However, under the DSR-IAS method, the sequential application of pre-emergence and post-emergence herbicides was carried out on 76% of the area (Table 4), while hand weeding was performed, along with the application of pre-emergence herbicides, on 12% of the area, leading to an increase in the cost of weed control. The novel herbicides being used in DSR production systems are costlier than the herbicides recommended in earlier PTR production systems [25]. A more complex weed flora was witnessed when using DSR methods, which lead to increased herbicide use. Amongst two DSR methods, a reduction in the use of herbicides under the DSR-PSI methods lead to a reduction in the cost of cultivation, thus helping to increase the economic returns of farmers.

5. Conclusions

It was concluded that weed infestation, herbicide use, and the cost of weed control were reduced under dry direct-seeded rice with pre-sowing irrigation as compared to dry direct-seeded rice with irrigation after sowing. Under the present situation of the declining water table in the Northwestern Indo-Gangetic plains, there is a need to promote the dry direct seeding of rice in moist field conditions after pre-sowing irrigation (DSR-PSI) in order to reduce herbicide use. This will lead to a decrease in the cost of cultivation, helping to obtain more net returns. Therefore, there is a need to popularize DSR-PSI technology among farmers by conducting training programs and front-line demonstrations in villages to create awareness among farmers. Further studies are required to evaluate the impact of a reduced herbicide load using this method. It is highly pertinent to conduct these studies in order to monitor the herbicide residue in soil, water, and crop produce under different methods of rice establishment.