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Highlight text Characterization and QTL identification of seedling-stage traits revealed relationships with nutrient uptake and grain yield; these traits may improve the adaptation and productivity of rice under direct-seeded conditions., The development of rice varieties for dry direct-seeded conditions can be accelerated by selecting suitable traits. In the present investigation, traits hypothesized to be important for direct-seeded conditions in rainfed systems, including seedling emergence, early vegetative vigour, nutrient uptake, nodal root number, and root hair length and density, were characterized to study the genetic control of these traits and their relationship with grain yield under seedling- and reproductive-stage drought stress. Two BC2F4 mapping populations derived from crosses of Aus276, a drought-tolerant aus variety, with MTU1010 and IR64, high-yielding indica mega-varieties, were developed and studied to identify quantitative trait loci (QTLs) that showed large and consistent effects. A total of 26 QTLs associated with 23 traits and 20 QTLs associated with 13 traits were mapped in the Aus276/3*IR64 and Aus276/3*MTU1010 populations, respectively. qGY6.1, qGY10.1, qGY1.1, and qEVV9.1 were found to be effective in both populations under a wide range of conditions. QTLs for several seedling-stage traits co-located with QTLs for grain yield, including early vegetative vigour and root hair length. On chromosome 5, several QTLs for nutrient uptake co-located with QTLs for root hair density and nematode gall rating. Six lines were selected from both populations based on grain yield and the presence of QTLs, and these lines typically showed improved seedling-stage traits (nodal root number, dry shoot weight, and root hair length and density). The co-located QTLs identified here can be used in research aimed at increasing the yield and adaptability of rainfed rice to direct-seeded conditions.

Barnyard grasses are serious weeds in direct seeded rice. We assessed the effectiveness of using controlled flooding for its control using two rice cultivars and two barnyard grasses contrasting in flood tolerance during germination. Flooding with 100 mm water after seeding suppressed barnyard grasses; but delaying flooding by 2-4 days was ineffective. Flooding increased the activity of alcohol dehydrogenase and pyruvate decarboxylase; the increase was higher in the tolerant rice cultivar but similar in both barnyard grasses. Aldehyde dehydrogenase activity increased only in flood-tolerant types of rice and weeds, but not in flood-sensitive types, implying potential role in tolerance., Crop productivity is largely affected by abiotic factors such as flooding and by biotic factors such as weeds. Although flooding after direct seeding of rice helps suppress weeds, it also can adversely affects germination and growth of rice, resulting in poor crop establishment. Barnyard grasses (Echinochloa spp.) are among the most widespread weeds affecting rice, especially under direct seeding. The present work aimed to establish effective management options to control these weeds. We assessed the effects of variable depths and time of submergence on germination, seedling growth and carbohydrate metabolism of (i) two cultivars of rice known to differ in their tolerance to flooding during germination and (ii) two barnyard grasses (Echinochloa colona and E. crus-galli) that commonly infest rice fields. Flooding barnyard grasses with 100-mm-deep water immediately after seeding was effective in suppressing germination and growth. Echinochloa colona showed greater reductions in emergence, shoot and root growth than E. crus-galli. Delaying flooding for 2 or 4 days was less injurious to both species. Echinochloa colona was also more susceptible to flooding than the flood-sensitive rice cultivar ‘IR42’. The activity of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) in rice seedlings was increased by flooding after sowing but with greater increases in ‘Khao Hlan On’ compared with ‘IR42’. The activity of ADH and PDC was enhanced to a similar extent in both barnyard grasses. Under aerobic conditions, the activity of ADH and PDC in the two barnyard grasses was downregulated, which might contribute to their inherently faster growth compared with rice. Aldehyde dehydrogenase activity was significantly enhanced in flood-tolerant ‘Khao Hlan On’ and E. crus-galli, but did not increase in flood-sensitive E. colona and ‘IR42’, implying a greater ability of the flood-tolerant types to detoxify acetaldehyde generated during anaerobic fermentation. Confirmation of this hypothesis is now being sought.

This study assessed the economic impacts of direct seeding of rice as an alternative crop establishment method for farmers in rice-wheat systems in Uttarakhand, Uttar Pradesh, and Bihar, India. Specifically, it examined the changes in farmers’ inputs (labor and materials) and level of productivity and incomes between direct-seeded (DSR) and transplanted (TPR) rice, and measured the economic returns on investment in direct seeding. Analyses included comparison of means, cost and return, and economic surplus framework. The average yield of DSR across sample farms in all three states was 5 percent lower than that of TPR. On the other hand, wheat yield increased by 9 percent after adopting DSR. The net present values (NPVs) of direct seeding in rice-wheat systems in Uttarakhand, Uttar Pradesh, and Bihar were USD 41 million, USD 32 million, and USD 44 million, respectively. The corresponding benefit-cost ratios were estimated at 46, 36, and 50. The NPVs of direct seeding in rice production alone in Uttarakhand, Uttar Pradesh, and Bihar were USD 33 million, USD 23 million, and USD 31 million, respectively. Hence, the greater proportion of benefits from DSR adoption was derived from the change in rice production. In sum, DSR is a profitable option in rice-wheat systems and is appropriate for diffusion.

This study has evaluated the technical efficiency of farmers engaged in rice-wheat cropping systems in North-eastern India, who are using Resource-Conserving Technologies (RCTs) such as Zero Tillage (ZT) and Direct Seeded Rice (DSR). These technology promotions are being carried out under the intervention of the Cereal Systems Initiative for South Asia (CSISA) project, primarily funded by the Bill and Melinda Gates Foundation. The resource-conserving technologies are being promoted as part of conservation agriculture supported by the project. The data used in this study have been derived from the socioeconomic surveys conducted in Eastern Uttar-Pradesh and Bihar in North-eastern India during the kharif season of 2009 and rabi season of 2010. A stochastic frontier analysis was carried out to investigate and compare the determinants of technical efficiency among the farmers receiving intervention and those who are not. The study has revealed that farmers receiving CSISA intervention have realized higher levels of technical efficiency. Additionally, farmers who are receiving subsidies and farmers who are planting more diversified crops have higher levels of technical efficiency.

International audience; Weeds cause substantive yield losses in rainfed rice, particularly direct-seeded rice (DSR). Two field experiments were conducted in 2005 in north-east Thailand to examine the effects of cutting date and timing of fertilizer application on suppressed weed, growth and yield of DSR. Treatments consisted of two fertilizer applications to the main plots (top-dressing at the date of cutting and 15 days after cutting; DAC) and four cutting dates of the sub-plots. Rice and weed cutting was performed at 30, 45, 60 and 75 days after seeding (DAS), compared with an untreated control. Cutting resulted in a higher growth rate and improved grain yield of rice compared to the untreated control. Weed cutting at 60 DAS resulted in the greatest leaf area index, which contributed to the maximum number of tiller as well as maximum plant dry mass when observed at 30 DAC. Lower densities and dry weights of weeds at 30 DAC were observed when cutting was done 60 DAS, resulting in a higher grain yield than the other cutting dates. Timing of fertilizer application had no significant effect on the density and dry weight of grasses and broad-leaved weeds, but did have a significant affected on, resulting in the lowest density of sedges at 45 DAC was observed with fertilizer applied at cutting date. Rice grain yield was higher with top-dressing of fertilizer at 15 DAC than with fertilizer applied at cutting date. The cutting treatments resulted in higher net incomes than the untreated control. These results indicate that rice and weed cutting at an appropriate growth stage is an alternative method to chemical weed control for DSR in rainfed riceland.

International audience; Phosphorus deficiency in soil and erratic rainfall limit rice production in Northeast Thailand. The objective of this study was to investigate rice’s response to different rates and times of phosphorus fertilizer. A field trial was conducted in a farmer’s field with a split plot design. Main plots were established using three rates: 15, 30, and 60 kg P ha-1. Five types of sub-plot were established as follows: (1) P fertilizer was applied by banding below the seeds’ depth before seeding (BBS), (2) broadcasting and incorporation into the soil before seeding, and (3) topdressing at three different DAS (days after seeding). Fertilizer was spread onto the soil surface at 10, 20, and 30 DAS. Significant grain-yield increases were affected by time or rate of fertilizer application. Grain yields were maximized by a rate of 60 kg P ha-1. Fertilizer application by BBS produced higher grain yield than did other treatments, giving higher root-length density and shoot growth, phosphorus uptake, and greater phosphorus-use efficiency than did fertilizer applied by broadcasting or delayed topdressing. BBS resulted in the highest phosphorus enrichment in soil volume with a rate of 60 kg P ha-1. The high solubility of fertilizer in a localized placement may satisfy the seedlings’ high initial demand of phosphorus and provide sufficient phosphorus availability to allow high productivity. Based on these data, in regions with low soil phosphorus availability where rainfall is also erratic, the management of sub-seed banding placement at the start of a crop at the rate of 60 kg P ha-1 is recommended as the optimum phosphorus fertilizer practice.

This article 'Chlorophyll meter threshold values for N management in wet direct-seeded irrigated rice' appeared in the International Rice Research Notes series, created by the International Rice Research Institute (IRRI) to expedite communication among scientists concerned with the development of improved technology for rice and rice-based systems. The series is a mechanism to help scientists keep each other informed of current rice research findings. The concise scientific notes are meant to encourage rice scientists to communicate with one another to obtain details on the research reported.