The rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping system is the largest agricultural production system worldwide, and is practised on 24 Mha in Asia. Many factors have threatened the long-term sustainability of conventional rice–wheat cropping systems, including degradation of soil health, water scarcity, labour/energy crises, nutrient imbalances, low soil organic matter contents, complex weed and insect flora, the emergence of herbicide-resistant weeds, and greenhouse-gas emissions. Options for improving the yield and sustainability of the rice–wheat cropping system include the use of resource-conservation technologies such as no-till wheat, laser-assisted land levelling, and direct-seeded aerobic rice. However, these technologies are site- and situation-specific; for example, direct-seeded aerobic rice is successful on heavy-textured soils but not sandy soils. Other useful strategies include seed priming, carbon trading and payment, the inclusion of legumes, and eco-friendly and biological methods of weed control. Irrigation based on soil matric potential using tensiometers can be useful for saving surplus water in direct-seeded, aerobic rice. These options and strategies will contribute to resolving water scarcity, saving labour and energy resources, reducing greenhouse-gas emissions, increasing soil organic matter contents, and improving the soil-quality index. Seed priming with various substances that supplement osmotic pressure (osmotica) is a viable option for addressing poor stand establishment in conservation rice–wheat cropping systems and for increasing crop yields. To strengthen the campaign for using resource-conservation technologies in rice–wheat cropping systems, carbon-payment schemes could be introduced and machinery should be offered at affordable prices. The persistent issue of burning crop residues could be resolved by incorporating these residues into biogas/ethanol and biochar production. Because rice and wheat are staple foods in South Asia, agronomic biofortification is a useful option for enhancing micronutrient contents in grains to help to reduce malnutrition.

Rice–wheat cropping systems in South Asia: issues, options and opportunities

With the advent of Green Revolution era in the mid-1960s, high-yielding wheat ( Triticum aestivum L.) varieties and chemical fertilizers were introduced in South Asia. Fertilizer consumption is continuously increasing since then, but the productivity of wheat is relatively stagnant during the last decade. In South Asia, fertilizers have been applied to wheat as blanket recommendations for regions with similar climate and landform. There exists a large variation in nutrient use efficiencies in wheat because of following blanket recommendations for nitrogen, phosphorus, and potassium in fields differing greatly in nutrient-supplying capacity of the soil. Research carried out in South Asia suggests that further improvement in nutrient use efficiency will become possible by balanced use of nitrogen, phosphorus, and potassium fertilizers, and by rational use of organic manures in wheat systems. Long-term fertility experiments also confirm the need of balanced use of nutrients to produce high sustainable yield levels of wheat. In saline alkali soils, wheat needs to be supplied with higher amounts of nutrients, particularly N, than in normal soils. Band placement of fertilizers, particularly phosphorus, leads to improved fertilizer use efficiency, but appropriate machinery is lacking. Recently introduced site-specific nutrient management strategies for wheat take into account field-to-field variability and can help increase fertilizer use efficiency more than that achieved by following blanket fertilizer recommendations. Conservation agricultural practices consisting of reduced tillage and residue retention in wheat fields have already been introduced in South Asia. Nutrient management strategies for these wheat-growing environments are also being actively worked out. Yield gap analysis shows that productivity of wheat as well as nutrient use efficiencies can be further improved.

Nutrient Management and Use Efficiency in Wheat Systems of South Asia

The rice-wheat cropping system is the most important agricultural production system in Indo Gangetic Plains in India. The productivity of this system is declining after 1990’s. The weeds are the major problem in the productivity of this system. In rice-wheat cropping system, the menace of Phalaris minor in wheat has threatened the productivity of wheat crop. Yield losses especially from Phalaris minor alone are estimated from 25 to 50 per cent and, under very severe infestations, the losses may go up to 80 per cent. Rice crop management system supports the survival of Phalaris. minor seed in rice-wheat system. The major weeds in rice are Echnichola spp., Digitaria sanguinalis, Commelina benghalensis, Celosia argentia, Cyperus rotundus, Cyperus iria and Cyperus rotundus . Weeds in wheat show resistance to isoproturon and cross resistance to the other herbicides. The rate of resistance evolution depends on the soil seed bank dynamics and selection intensity, with selection intensity having the greatest impact. The study of the weed dynamic in rice-wheat cropping system helps the researchers and farmers to formulate the strategies for the control of weeds. In this chapter has discussed the impact of weeds, weed seed bank, various management practices for control of weeds. Weed dynamic can be controlled effectively by the conservation tillage which includes crop rotation, cover crops and reduced tillage.

/pdf/weed-dynamics-in-rice-wheat-cropping-system-45kvhxv1no.pdf

Weed dynamics in rice-wheat cropping system

1Department of Plant Breeding and Genetics. Mungbean [Vigna radiata (L.) Wilczek], also known as greengram, is the third most widely cultivated pulse crop in India. Pulse crops have been the mainstay of Indian agriculture for providing protein-rich diet to vegetarian masses of the country. Being leguminous crops they have beneficial effect on improving soil fertility through fixation of atmospheric nitrogen. Summer mungbean often suffers from severe crop-weed competition because it is grown under irrigated conditions. Infestation of weeds is a major constraint in achieving higher yield of summer mungbean (Singh and Sekhon, 2002), as these compete with crop plants for nutrients, moisture, light and space. The magnitude of reduction in yield depends upon the weed flora present, quantum of weed flora and duration of crop-weed competition. Critical period for crop-weed competition in summer mungbean is from 15 to 30 days after sowing (Singh et al., 1996). Thus, it is imperative to eliminate weeds from the crop at proper time and with suitable methods. Though weeds can be controlled by hoeing yet due to shortage of labour it becomes difficult to do hoeing at appropriate time and delayed hoeing may cause economic loss. A field experiment was conducted at the Punjab Agricultural University, Ludhiana, India during summer 2003 to study the effect of weed control in summer mungbean. Ludhiana (Latitude 30° 56′ N, longitude 75° 52′ E, altitude 247 m above the sea level) is located in the sub-tropical region. The soil of the experimental field was loamy sand in texture, having pH 8.2, low in organic carbon (0.33%), low in available nitrogen and medium in available phosphorus and potassium content. Twelve treatments viz., unweeded check, one and two hoeings [25 and 45 days after sowing (DAS)], two hoeings with wheel hoe (25 and 40 DAS), fluchloralin 0.625 kg/ha, trifluralin 0.96 kg/ha, pendimethalin 0.45 and 0.75 kg/ha, quizalofop-ethyl 35 and 50 g/ha and chlorimuron-ethyl 9 and 15 g/ha were tested in a randomized complete block design with four replications and net plot size was 4.5 x 2.025 m. The crop was sown on 28 March, 2003 in row spacing of 22.5 cm using a recommended seed rate of 37.5 kg/ha of variety SML 668. The pre-plant incorporation of fluchloralin and trifluralin and pre-emergence application of pendimethalin was done on the same day at the time of sowing and after sowing of the crop, respectively. The post-emergence application of quizalofop and chlorimuron was done 20 DAS using knapsack sprayer fitted with a flat-fan nozzle. Two hand hoeings were done at 25 and 40 days after sowing using khurpa (a small hand operated tool) and wheel hoe in respective treatments. Four irrigations were given to the crop : 1st on 13th April, 2nd on 23rd April, 3rd on 2nd May and 4th on 28th May. Data on weed count and weed dry matter were recorded 25 and 40 DAS and at harvest, using a quadrat measuring 50 x 50 cm. Data on nodulation and plant growth were recorded 25 DAS and data on yield and yield attributes were recorded at harvest. Weed as well as plant samples were analyzed for nutrient (nitrogen, phosphorus and potassium) uptake at harvest. The data were analyzed and treatments having a significant F value, critical difference (CD) values were calculated at 5% probability level.

effect of weed management on weeds, nutrient uptake, nodulation, growth and yield of summer mungbean (Vigna radiata)

Dynamics Of Micronutrient Cations In Soil-Plant System As Influenced By Long Term Application Of Chemical Fertilizers And Amendments In An Acid Alfisol

A field experiment was conducted during the Kharif season of 2006 and 2007 at G.B. Pant University of Agriculture and Technology, Pantnagar to find out the most effective weed control method under different sowing dates in direct-seeded unpuddled rice. Highest grain yield (2.5–2.7 t/ha) was recorded from 20 June sowing. The grain yield was the highest in mechanical weedings at 20 and 40 DAS. Pendimethalin 1.0 kg/ha + anilophos 0.4 kg/ha (pre-emergence) produced significantly higher grain yield (3.1–3.3 t/ha) over rest of the herbicidal treatments. Uncontrolled weeds reduced the grain yield of rice by 67–70%.

Sowing time and weed management practices to enhance yield of direct-seeded rice

An experiment was conducted during 1989-90 and 1990-91 to study the effect of summer green-manuring with 2 species of Sesbania, viz S. cannabina (Retz.) Pers. and S. rostrata Berm., and nitrogen in rice (Oryza sativa L.)-wheat (Triticum aestivum L. emend. Fiori & Paol.) cropping system. S. cannabina added 7.4 tonnes/ha dry biomass containing 186 kg N/ha and S. rostrata added 8.5 tonnes/ha biomass containing 252 kg N/ha. N available to rice crop from S. rostrata was equivalent to 80 kg urea N. Highest rice (7 180 kg/ha) and wheat (3 549 kg/ha) yields were obtained from green-manuring with S. rostrata and 120 kg urea N/ha applied to rice crop. In this treatment the total N removal by rice and wheat crops was 179 kg/ha. This treatment left positive balance of N (270 kg N/ha) in the soil. The mineralization of N added through Sesbania species was most rapid during the first 20 days after transplanting.

Effect of Sesbania green-manure and nitrogen fertilizer in rice (Oryza sativa)-wheat (Triticum aestivum) cropping system

A field experiment was conducted during Kharif season of years 2011 and 2012 at Norman E. Borlaug crop research centre of Govind Ballabh Pant University of Agriculture & Technology, Pantnagar (U.S. Nagar), Uttarakhand. Fluazifop-p-butyl + fomesafen controlled grasses and non-grassy weeds effectively and recorded 29.3 weeds/m2 in 500 g/ha against (171.17/m2) in untreated check. However, the grain yield was highest (2.21 t/ha) in the treatment of weed free followed by fluazifop-p-butyl + fomesafen applied 313 g/ha as post-emergence (2–5 leaf stage of weeds). Biomass of weeds was also lowest in fluazifop-pbutyl + fomesafen 313 g/ha treated plots. However, total weed density was lowest in fluazifop-p-butyl + fomesafen 500 g/ha treated plot but this dose showed toxic effects on crop. Weed index was lowest (7.8%) in the treatment of fluazifop-p-butyl + fomesafen 313 g/ha and highest in untreated (63.5%).

Promising early post-emergence herbicides for effective weed management in soybean

An experiment at Crop Research Centre of G.B. Pant University of Agric. and Tech., Pantnagar in split-plot design during two consecutive years (1991–92 and 1992–93) was conducted during both the seasons (kharif, rice and rabi, wheat). During kharlf season, among rice cultures grain yield was significantly higher (4137 kg/ha during 1991 and 3892 kg/ha during 1992) in transplanted rice over direct sowing either puddled or non-puddled during both the years. Lowest yield (2380 kg/ha during 1991 and 1975 kg/ha during 1992) was obtained in direct sowing unpuddled conditions. Complete failure of the crop was recorded in direct sown (non-puddled) rice during both the years. Both the herbicides pendimethalin and butachlor were equally effective. Grain yield of wheat was not much influenced due to puddled/non-puddled soils (in kharif) during both the years.

Weed Management in Different Rice Cultures and their Effects on Wheat Grown in Rice-Wheat Sequence

The data from the field experiments conducted during Kharif seasons of 1985 and 1986 at Crop Research Centre of CB Pant University of Agriculture and Technology, Pantnagar (Distt Nainital) UP revealed that the highest nutrients were taken up by the grassy weeds than broad leaf weeds The uptake of the N,P,K by total weeds was markedly reduced and uptake of these nutrients by crop plants was increased at narrow row spacing(30cm) as compared to the wider row spacing (60 cm) Highest uptake by weeds and lowest uptake by crop plants was estimated in the weedy check plots Among weed control treatments, the uptake by weeds was less in the treatment of alachlor 25 kg/ha and two hand weedings (20+40 das)

Influence of Row Spacing and Weed Management on the Nutrient Uptake by Soybean (Glycine Max (L) Merrill and Associated Weeds

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