The High Barind Tract: a challenging drought-prone agricultural environment

The Barind Tract is a distinctive physiographic unit comprising a series of uplifted blocks of terraced land covering 8,720 km2 in northwestern Bangladesh between the floodplains of the Padma (known as the Ganges in India) and the Jamuna rivers (the main channel of the lower Brahmaputra). Spread over parts of the greater districts of Rajshahi, Dinajpur, Rangpur, and Bogra of Bangladesh, and Maldah District of West Bengal in India, the Barind includes 773,000 ha in Bangladesh, of which 532,000 ha are cultivable. Rainfall is comparatively low in this region, with the long-term average being about 1,250 mm in the west and 2,000 mm in the northeast, occurring mainly from late April to October. With a variable rainfall and temperature ranging from 25 to 35 °C (regularly exceeding 40 °C) in the monsoon season, the area is considered semiarid and drought-prone. The aman rice1 (monsoon)-growing season ranges from 180 days in the west to 220 days in the northeast but the frequency of dry periods, particularly in July and August, is the highest in the country. The Barind is at a comparatively higher elevation than the adjoining floodplain and there are two terrace levels—one at 40 m above sea level and the other between 19.8 and 22.9 m. Therefore, when the floodplains go under water during the monsoon,the Barind Tract remains relatively free from flooding and is drained by a few small streams. About 47% of the Barind region is classified as highland, about 41% as medium highland, and the rest is lowlands. Although 55% of the Barind was forest in 1850, subsequent rapid population growth resulted in 70% of the land being converted to arable land by 1970. The area is now characterized by terraced slopes with bunded fields without water control other than drainage by gravity to lower-lying fields and streams

Issues related to direct seeding of rice in rainfed cropping systems in northwest Bangladesh

Economic factors and developments in rice production technologies are the major drivers that have led to the adoption of direct seeding of rice in place of transplanting in Asia. The primary economic motives for a shift to direct seeding are the savings in labor cost and the possibility of crop intensification. A key development challenge in the drought-prone rainfed agriculture of the Barind Tract of northwest Bangladesh is to simultaneously improve the reliability and yield of monsoon rice while improving total system productivity by increasing the area planted to drought-tolerant postrice crops. Research trials and field-scale evaluation by farmers have demonstrated that dry direct seeding or wet seeding of pregerminated rice seed reduces labor for crop establishment, results in rice yields similar to or higher than those from conventional transplanting, and advances harvest by 7-10 days. Earlier harvest has the potential to reduce the risk of terminal drought in rice when the monsoon ends abruptly and increases the opportunity for establishing a postrice crop of chickpea on residual moisture. Herbicide use is essential with direct seeding and this further reduces rice production costs. This modified rice/legume system using direct seeding is knowledge-intensive. Widespread sustained adoption will depend on farmers undertaking timely tillage, adequate land leveling, and timely application of herbicides. Extension/farmer training supported by clear decision support frameworks will be needed to provide farmers with access to the knowledge needed to implement direct seeding effectively

Improved weed management for transplanted aman rice

Rainfed transplanted rice grown in the monsoon aman season accounts for more than 50% of the total area planted to rice in Bangladesh. Because of rising input costs, including labor, farmers are searching for ways to maintain income, by either increasing yields or reducing costs or both. On-farm trials in the High Barind Tract indicated that one-third of the farmers would be able to gain 0.5 t ha–1 or more additional grain by undertaking more intensive or timelier weeding than is usual under current management practices. Higher yields were observed on-farm from a preemergence application of butachlor(1.25 kg a.i. ha–1) compared with hand weeding twice. In Comilla District, trials of a range of weed management practices demonstrated that the yield advantage over the farmers’ practice, either one or two hand weedings, was on average 355 ± 18 kg ha–1 for Rifit (pretilachlor), 281 ± 39 kg ha–1 for Machete (butachlor), and 210 ± 34 kg ha–1 for Ronstar (oxadiazon), each followed by one hand weeding in aman 2003. Partial budgets calculated for inputs and returns showed that hand weeding was less profitable than herbicides in rainfed rice,incurring US$72 ha–1 lower return. Use of a push weeder plus one hand weeding was less profitable than herbicides, incurring$49 ha–1 lower return. To date, herbicides have been largely promoted for irrigated rice in Bangladesh. The trial results demonstrate that under rainfed conditions early in the aman season, water levels are adequate for herbicides to work effectively. The use of herbicides allows timely weed control when there is a shortage of labor and avoids transaction costs, such as the provision of meals and time needed to source laborers. Herbicides are likely to be adopted by growers experiencing labor shortages, particularly on large farms and for farmers seeking to reduce input costs. Sharecroppers and tenant farmers who pay rent are primarily concerned about obtaining a high aman yield, so innovations that raise aman yields (such as herbicides that will have a similar effect as a timely first weeding) are also likely to be adopted on sharecropped plots, even when costs are not shared between the landlord and tenant

Whole-genome sequencing reveals host factors underlying critical COVID-19

Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease

Proceedings

1 fig. 3 tab. 22 ref. Sum. (En)Itchgrass (Rottboellia cochinchinensis) is a serious and persistent weed problem in many tropical agricultural and conservation areas. In Central America it is one of the most noxious and serious weeds in several upland crops, causing severe yield losses. Experimentally, pre-emergence control with herbicides, weed elimination during the fallow period and zero tillage reduced itchgrass populations in comparison to conventional practices used growers (no fallow management, soil preparation by disc harrowing and limited use of in-crop herbicides. Additional improvement in itchgrass management is brought about by inter-sowing legume cover crops. Of several legumes evaluated, mucuna (Mucuna deeringiana) and Canavalia ensiformis controlled the weed better and covered the soil, especially if planted simultaneously with maize. Itchgrass suppression by mucuna usually corresponded with increased grain yields but competition by the cover crop could reduce yields a good compromise is to delay mucuna planting by two weeks in relation to maize. Integrated tactics to control itchgrass were evaluated in on-farm validation plots. Pendimethalin controlled itchgrass at the onset of validation plots and facilitated the establishment of the cover crop. Itchgrass densities were lower in validation plots than in grower's fields while infestation levels and the soil seed bank decreased over three years with integrated management. In general, corn yields were also higher in validation plots. Integrated itchgrass management also proved economically feasible for smallholders. A promising alternative is biological control with the itchgrass smut, Sporisorium ophiuru, which prevents seed set and its host specifi