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\nHIGHLIGHTSA greenhouse experiment was conducted from 2015–2016 to 2017–2018 on an Aeric Haplaquept to evaluate the effect of irrigation (surface irrigation at furrows at irrigation water: cumulative pan evaporation = 1, drip irrigation to meet 100%, 80% and 60% of actual crop evapotranspiration demand), and mulch (nonwoven jute agro textile, biodegradable plastic film, rice straw and no mulch) regimes on strawberry. Average soil water storage in root zone (86 mm) and fraction of potential plant available water (61%) was highest in jute agrotextile mulched and drip irrigated at 80% actual evapotranspiration. This combination of mulch and irrigation regime increased belowground (root length density, 7.15 × 103 mm−3) and above ground (leaf area index, 9.4) crop growth and emerged as the best option with three- and four-times higher yield (31.1 Mg ha−1) and water use efficiency (23.1 kg m−3), respectively than surface irrigated unmulched strawberry. Results suggest that these findings be incorporated into packages and practices of strawberry cultivation in the moist tropical sub-humid region of Bengal basin and other similar agroecological regions of South Asia.Growing strawberries with drip irrigation to meet 80% of the crop’s evaporative demand, coupled with jute agro-textile mulch, enhanced yield and water use efficiency three and four times more, respectively, compared to surface irrigation without mulch.After irrigation, redistributing total soil water in the root zone resulted in a 25% increase for 1.0 ETc and a 22% increase for 0.8 ETc compared to surface irrigation.Site-specific Kc values of strawberry were estimated.Established the relationship of Kc with leaf area index and growing degree-days.Growing strawberries with drip irrigation to meet 80% of the crop’s evaporative demand, coupled with jute agro-textile mulch, enhanced yield and water use efficiency three and four times more, respectively, compared to surface irrigation without mulch.After irrigation, redistributing total soil water in the root zone resulted in a 25% increase for 1.0 ETc and a 22% increase for 0.8 ETc compared to surface irrigation.Site-specific Kc values of strawberry were estimated.Established the relationship of Kc with leaf area index and growing degree-days. [ABSTRACT FROM AUTHOR]

Inherently poor soil fertility and non-adoption of fertilizer recommendations based on soil test and yield targets by farmers limit the productivity and profitability from monsoon rice in Bangladesh and much of South Asia. In the Level Barind Tract (LBT; AEZ-25) and the High Ganges River Floodplain (HGR; AEZ-11) agro-ecological zones (AEZs) of Bangladesh, monsoon (aman/kharif) season transplanted rainfed rice (known as T. aman rice) is grown in large areas after maize, wheat and/or mungbeans, with residues of each crop removed from the field after grain harvest. This results in lower grain yield and lower profits in these AEZs as compared with other AEZs. Nutrient management, based on soil test, yield targets, or integrated use of inorganics and organics for each AEZ together with retention of crop residue, has the potential to increase rice yield, reduce production cost and increase income. With this hypothesis, this study was conducted to determine the optimum nutrient management practices for achieving higher yield, maintaining apparent soil nutrient balance, and obtaining high profits from monsoon rice. Twelve nutrient management options were evaluated, of which the first six were: (i) 80-16-44-12-2 kg ha-1 of N, P, K, S, Zn respectively for a high yield goal (T1; ‘HYG’); (ii) 56-12-32-8- 1.5 kg ha-1 respectively for a medium yield goal (T2; ‘MYG’); (iii) 65-13-32-9-2 kg ha-1 respectively plus 5 t ha-1 cowdung as integrated plant nutrient management system (T3, ‘IPNS’); (iv) 67-14-41-9-2 kg ha-1 respectively as a soil test-based fertilizer management strategy (T4; ‘STB’); (v) 40-9-11-0-0 kg ha-1 respectively as per farmers’ practice (T5; ‘FP’) and (vi) 0-0-0-0-0 kg ha-1 as a control (T6; ‘CON’). The remaining six treatments were the same as above but each also included the crop residue incorporation (CRI), i.e., (vii) T7, ‘HYG+CRI’; (viii) T8, ‘MYG+CRI’; (ix) T9, ‘IPNS+CRI’; (x) T10, ‘STB+CRI’; (xi) T11 ‘FP’+CRI’; and (xii) T12, ‘CON+CRI’. In both AEZs, STB plus CRI resulted in the highest rice yield (p≤0.05) followed by ‘STB’ and ‘IPNS+CRI’. In comparison with ‘FP’ and ‘CON’, each without CRI, balances were positive (p≤0.05) for P, S, Zn and B but were negative for N and K in ‘HYG’, ‘MYG’, ‘IPNS’ and ‘STB’ with or without CRI. In both AEZS, STB nutrient management had the highest (p≤0.05) net returns (526 & 487 US$ ha-1, respectively), highest benefit cost ratio (BCR; 3.54 & 3.36) and highest marginal benefit cost ratio (MBCR; 10.47 & 10.19). These were followed by STB+CRI’ and ‘IPNS’, while they were lowest (p≤0.05) for CON and FP. We recommend that nutrient application, based on soil test with incorporation of mungbean residue, followed by IPNS, could be the best strategies for achieving high yield, improving soil fertility and for fetching a higher profit from monsoon rice in Bangladesh and similar soils and growing environments of South Asia.

It is important to identify and develop stable wheat varieties that can grow under heat stress. This important issue was addressed in Bangladesh using six wheat genotypes, including three existing elite cultivars (‘BARI Gom 26’, ‘BARI Gom 27’, ‘BARI Gom 28’) and three advanced lines (‘BAW 1130’, ‘BAW 1138’, ‘BAW 1140’). Six sowing dates, namely early sowing (ES) (10 November), optimum sowing (OS) (20 November), slightly late sowing (SLS) (30 November), late sowing (LS) (10 December), very late sowing (VLS) (20 December) and extremely late sowing (ELS) (30 December) were assessed over two years in four locations, representative of the diversity in Bangladesh’s agro-ecological zones. In a split plot design, sowing dates were allocated as main plots and genotypes as subplots. A GGE biplot analysis was applied to identify heat tolerance and to select and recommend genotypes for cultivation in heat-prone zones. All tested genotypes gave greatest grain yield (GY) after OS, followed by SLS, ES and LS, while VLS and ELS gave smallest GY. When GY and the correlations between GY and stress tolerance indices were considered, ‘BAW 1140’, ‘BARI Gom 28’ and ‘BARI Gom26’ performed best under heat stress, regardless of location or sowing date. In contrast, ‘BARI Gom 27’ and ‘BAW 1130’ were susceptible to heat stress in all locations in both years. Ranking of genotypes and environments using GGE biplot analysis for yield stability showed ‘BAW1140’ to be most stable, followed by ‘BARI Gom 28’ and ‘BARI Gom 26’. Wheat sown on November 20 resulted in highest GY but that sown on December 30 resulted in lowest GY in both years. In conclusion, ‘BAW 1140’, ‘BARI Gom 28’ and ‘BARI Gom 26’ are the recommended wheat genotypes for use under prevailing conditions in Bangladesh.

In South Asia, including Bangladesh, most farmers sow wheat under residual soil moisture after rice is harvested, but the upper layer of soil dries quickly after soil has been prepared for wheat sowing. Crop seeds that are sown either deeply or shallowly can result in failed emergence, low dry matter accumulation, and reduced grain yield. Therefore, appropriate sowing depth is crucial for seedling emergence and successful crop establishment. Considering this, a two-year field experiment was conducted at the research field of the Agricultural Research Station of the Bangladesh Agricultural Research Institute at Dinajpur during the dry, rabi (winter) season of 2013-14 and 2014-15, at four sowing depths, i.e., 2, 4, 6 and 8 cm, to identify the most appropriate sowing depth for higher grain yield. Wheat seeds sown at a depth of 4 cm resulted in significantly highest number of seedlings and seminal roots, tallest plants as well as largest roots and plant biomass followed by sowing at a depth of 6, or 2 cm. Depth of sowing also significantly affected the yield and yield-related attributes, all performing best at a depth of 4 cm. The highest number of spikes m-2, grain yield, straw yield and harvest index were observed when seeds were sown at depths of 4 or 6 cm, relative to 2 or 8 cm. Therefore, a sowing depth of 4 to 6 cm is recommended for wheat cultivation in South Asia, including Northern Bangladesh.

Information on soil potassium (K) supplying capacity, K-depletion, and contribution of exchangeable and non-exchangeable K in wetland rice ecology is limited. Understanding of K dynamics of different soil types can be a guideline for better K-fertilizer management and sustainable soil K use to achieve sustainable rice yields. To understand this soil K-supplying capacity to rice plants, a pot study with two K levels (K0 and K100 mg K kg-1 soil) was conducted with seven successive rice crops grown up to the panicle initiation stage using 18 different soils collected from across Bangladesh. The cumulative soil K-supplying capacity (242–758 mg K kg-1 soil) varied significantly (P ≤.001) among soils, showing a strong positive relationship (R2 = 0.78) with NH4OAc K. The potential K-supplying capacity of these soils was the highest (758 mg K kg-1 soil) in Mithapukur (AEZ 3-Tista Meander Floodplain) and the lowest (242 mg K kg-1 soil) in Barura (AEZ 19-Old Meghna Estuarine Floodplain). In K0 soils, the successive cycles of rice resulted in continuous depletion of both non-exchangeable and exchangeable K pools. The concentration of both exchangeable and non-exchangeable K was maintained and almost balanced in K100 soils compared to K0 with successive rice cropping. Non-exchangeable K contribution to K nutrition of rice plants during the seventh cropping ranged, respectively, from 83% to 93% and 26% to 55% in K0 and K100 soils. Results reveal the importance of a non-exchangeable K pool in K-supplying to plants in wetland rice production systems with different soil types. [ABSTRACT FROM AUTHOR]

Nepalese community forests are globally recognized for sustainable forest management and improving the livelihoods of forest-dependent communities, but their contribution to carbon sequestration in trees and soil is rarely studied. This study was performed to understand the effect of management practices on carbon stock of two community forests (CFs) - Taldanda (managed) and Dangdunge (unmanaged) - dominated by Sal (Shorea robusta) in the mid-hills of Nepal. Twenty-one concentric sample plots, each of 250 m2, were laid out in each forest to estimate different carbon pools and a stratified random sampling intensity of 0.5% used to collect data. Results showed significant (p<0.05) differences in above and below-ground biomass and carbon sequestration potential between the two CFs. The managed and unmanaged forests had total carbon stock of 269.3±27.4 and 150.0±22.7 ton/ha, respectively, demonstrating 1.79 times higher carbon stock in the former than the latter. The managed forest had significantly (p<0.05) greater mean soil organic carbon (SOC) stock than the unmanaged forest. The SOC was highest in the upper soil layer (0-10 cm), with a steady decrease as the soil depth increased. All other measured carbon pools values were higher in managed compared to unmanaged forest. The difference in carbon stock was due to the manipulation of different forest management activities, including thinning, timber extraction, fire control, grazing, and fuel wood/fodder extraction. The study suggests that the implementation of proper forest management would be necessary for enhancing carbon stock in forest trees and soils. [ABSTRACT FROM AUTHOR]

Effective broad-spectrum herbicides are needed to address the issues of herbicide resistance and weed shifts in common cropping systems. A field experiment was conducted in 2016 and 2017 in West Bengal, India to compare the performance of three post-emergence herbicides (bispyribac-sodium; fenoxaprop-p-ethyl; penoxsulam) in monsoon rice (Oryza sativa L.) and their residual effects on succeeding rapeseed (Brassica rapa L.). Rice yield loss due to competition with Echinochloa colona (L.) Link, Leersia hexandra Sw., Cyperus iria L., Ludwigia parviflora L., and Monochoria vaginalis (Burm f.) C. Presl. Ex Kunth was 64% compared with weed-free control. Bispyribac-sodium 10% SC applied at 30 g a.i. ha−1 20 days after transplanting reduced weed density over the weedy control, ranging from 37% (M. vaginalis) to 87% (L. hexandra). Fenoxaprop-p-ethyl and penoxsulam applied, respectively, at 86 and 20 g a.i. ha−1 were effective in controlling grasses, but less effective against sedges and broadleaves. Bispyribac-sodium application resulted in highest rice yield (5.45 t ha−1), net return (Indian Rupees 42,677 ha−1), and benefit cost ratio (1.72). Bispyribac-sodium had neither adverse effect on soil microbes nor phytotoxic effect on rice and subsequent rapeseed. We recommend bispyribac-sodium for weed control in transplanted rice under rice-rapeseed system in eastern India. [ABSTRACT FROM AUTHOR]

Nepal is a major rice producer of South Asia, feeding more than 20 million people of the country and abroad. However, productivity and profitability of rice are low in Nepal compared to other regional countries. Large yield gaps exist between attainable and farmers' yields and nutrient management is identified as one of the major reasons. Nutrient Expert® (NE), a decision-support tool based on site-specific nutrient management (SSNM) principles has been validated and applied in many countries of Asia and Africa as new recommendation protocol for nutrient management in selected crops, including rice. Present study used NE® Rice as nutrient management protocol in farmers' fields across Terai and mid-hills regions of Nepal during 2014–2018. The study revealed that NE-based fertilizer recommendations resulted in increase in yield over 2.0 t.ha−1 (p ≤ 0.05) and double the profits compared to existing blanket fertilizer recommendation, and farmers' fertilizer practice. Due to large variations in slope, altitude, soil, and management, performance of NE® varied across locations. Its performance was better in Terai due to flat lands and less variations in soil types, compared to sloping lands and varied soils of mid-hills. NE tool provided adequate guidance to apply the required rate of fertilizer that matched the crop requirement and soil nutrient supply of each farmer fields. The novelty of the study is introduction of a dynamic fertilizer recommendation approach that can supplement the existing static blanket recommendation system. We conclude that Nutrient Expert® - Rice can be considered as an effective tool for nutrient recommendation for rice in Nepal. [ABSTRACT FROM AUTHOR]

Field studies were conducted under a conservation-tilled rainfed semi-arid environment in New Delhi, India, during the rainy- and winter-seasons of 2010-11 and 2011-12 to assess the effects of diverse crops and cropping systems and residue retention on system productivity and profitability of nine double-cropping systems. Pearlmillet (Pennisetum glaucum (L.) R. Br.), clusterbean (Cyamopsis tetragonoloba L.) and greengram (Vigna radiata L. Wilczek) were grown under no-residue, crop residues, and Ipil-ipil (Leucaena leucocephala) twigs during the rainy season in 2010 and 2011. Subsequently, wheat (Triticum aestivum L.), chickpea (Cicer arietinum L.), and mustard (Brassica juncea L.) were grown during winter of 2010-11 and 2011-12 after summer crops. Randomized Complete Block, Strip and Strip-plot designs with four replications were followed to analyze the data from the nine rainfed cropping systems with different residue management practices. Significantly higher (p ≤ 0.05) pearlmillet-equivalent yield was obtained with clusterbean after wheat and chickpea under Leucaena twigs, followed by residue retention than pearlmillet or greengram. Significantly higher (p ≤ 0.05) wheat-equivalent yield (4.15 t ha-1 in 2010-11, and 3.77 t ha-1 in 2011-12) was obtained with mustard under Leucaena twigs after clusterbean. The system profitability (net returns and B: C ratio) were higher under clusterbean-mustard and clusterbean-wheat systems with Leucaena twigs. It is suggested that the clusterbean-mustard, greengram-wheat and pearlmillet-chickpea systems with Leucaena twigs were the most beneficial systems under zero-tilled rainfed conditions in the semi-arid environments of north-western India. [ABSTRACT FROM AUTHOR]

Fertigation has the potential to reduce extra chemical load by improving nutrient and water use efficiency of coconut (Cocos nucifera L.), but studies demonstrating the fertilizer reduction through drip irrigation in comparison to conventional ring basin method are rare in the Eastern Indo-Gangetic Plains (IGP) of South Asia. A long-term field experiment was conducted during 2007-2013 in West Bengal, India, to study the effect of fertigation on coconut var. DXT. The experiment was laid out in a randomised complete block design (RCBD) with six treatments (control - no fertilizers and water applied with drip irrigation; 25%, 50%, 75% and 100% of the recommended dose of fertilizer (RDF), each applied with drip irrigation; and 100% of the RDF and water applied with ring basin method of irrigation (i.e., conventional method)). Nuts yield was significantly higher for 75% of RDF (24.44 t ha−1 year−1) followed by 100% of RDF, each drip irrigation (23.79 t ha−1 year−1) compared to control (21.89 t ha−1 year−1). Copra yield was significantly higher for 75% of RDF (3.19 t ha−1) compared to 100% of RDF (3.12 t ha−1) and no fertilizer (1.87 t ha−1). Nitrogen (N), phosphorus (P) and potassium (K) contents of soil increased by 4.9%, 10.4% and 9.4%, respectively, with 75% of RDF applied through drip irrigation. Microbial population showed inverse relationship with amount of fertilizer application. The most water-use efficient fertigation treatment was 75% RDF (13.48 kg copra m−3) followed by 100% RDF (13.18 kg copra m−3) with drip irrigation as compared to conventional way soil application of fertilizers through ring basin method of irrigation (4.23 kg copra m−3). Role of N on yield variability was most prominent by both available soil N status (R2 = 0.49**) and leaf N concentration (R2 = 0.51**). The study indicated that there is a great scope for reducing the N, P and K fertilizers by up to 25% of the present RDFs for coconut when applied through drip irrigation compared to ring basin method of irrigation for its higher productivity and profitability through efficient use of nutrients and water in the Eastern IGP of South Asia. [ABSTRACT FROM AUTHOR]

Increased nutrient withdrawal by rapidly expanding intensive cropping systems, in combination with imbalanced fertilization, is leading to potassium (K) depletion from agricultural soils in Asia. There is an urgent need to better understand the soil K-supplying capacity and K-use efficiency of crops to address this issue. Maize is increasingly being grown in rice-based systems in South Asia, particularly in Bangladesh and North East India. The high nutrient extraction, especially K, however, causes concerns for the sustainability of maize production systems in the region. The present study was designed to estimate, through a plant-based method, the magnitude, and variation in K-supplying capacity of a range of soils from the maize-growing areas and the K-use efficiency of maize in Bangladesh. Eighteen diverse soils were collected from several upazillas (or sub-districts) under 11 agro-ecological zones to examine their K-supplying capacity from the soil reserves and from K fertilization (100 mg K kg-1 soil) for successive seven maize crops grown up to V10-V12 in pots inside a net house. A validation field experiment was conducted with five levels of K (0, 40, 80, 120 and 160 kg ha-1) and two fertilizer recommendations based on "Nutrient Expert for Maize-NEM" and "Maize Crop Manager-MCM" decision support tools (DSSs) in 12 farmers' fields in Rangpur, Rajshahi and Comilla districts in Bangladesh. Grain yield and yield attributes of maize responded significantly (p < 0.001) to K fertilizer, with grain yield increase from 18 to 79% over control in all locations. Total K uptake by plants not receiving K fertilizer, considered as potential K-supplying capacity of the soil in the pot experiment, followed the order: Modhukhali > Mithapukur > Rangpur Sadar > Dinajpur Sadar > Jhinaidah Sadar > Gangachara > Binerpota > Tarash > Gopalpur > Daudkandi > Paba > Modhupur > Nawabganj Sadar > Shibganj > Birganj > Godagari > Barura > Durgapur. Likewise, in the validation field experiment, the K-supplying capacity of soils was 83.5, 60.5 and 57.2 kg ha-1 in Rangpur, Rajshahi, and Comilla, respectively. Further, the order of K-supplying capacity for three sites was similar to the results from pot study confirming the applicability of results to other soils and maize-growing areas in Bangladesh and similar soils and areas across South Asia. Based on the results from pot and field experiments, we conclude that the site-specific K management using the fertilizer DSSs can be the better and more efficient K management strategy for maize. [ABSTRACT FROM AUTHOR]

A field experiment was conducted during the two consecutivekharifseasons of 2011 and 2012 on sandy-loam lateritic soil of Indian subtropics to investigate the impact of integrated nutrient management (INM) on crop productivity, nutrient use efficiency of applied nutrients and soil fertility in restoring sustainability with hybrid rice cultivation. Application of 50% recommended dose of fertilizer (RDF) + 50% recommended dose of nitrogen (RDN) through mustard oil cake (MOC) or 75% RDF + 25% RDN through MOC + biofertilizer recorded significantly higher grain and biomass yields, greater NPK removal and higher partial factor productivity of applied nutrient (PFPN) than those of the crop having 100% RDF, 100% RDN through MOC and 25% RDF + 75% RDN through MOC, which showed very poor performance. The former treatments also improved organic carbon and available NPK contents in soil in spite of greater removal of NPK by the crop. Results of study suggested integrated use of 50% RDF + 50% RDN through MOC or 75% RDF + 25% RDN through MOC + biofertilizer for increasing hybrid rice productivity, PFPN and improving soil fertility for sustainability. [ABSTRACT FROM PUBLISHER]

Responding to increasing demand from poultry and fish feed industries, maize area is rapidly expanding in South Asia. Current tillage and crop establishment (TCE) practices are however associated with high levels of input use, including direct and indirect forms of energy. In Bangladesh, policy makers emphasize the need to reduce the USD 1.4 billion year −1 agricultural energy subsidy. Bangladeshi farmers cultivate maize during the winter rabi season, when yield potential is high. But when poorly managed, farmers’ investments in TCE practices may erode farm-level profitability, while inefficiently utilizing energy. Resource-conserving TCE options may however provide an alternative for maintaining or raising yields, while increasing farmers’ income and reducing energy use. We present a multi-criteria assessment of the productivity, profitability and energetics of alternative TCE options, including zero (ZT), reduced (RT), and strip tillage (ST), in addition to fresh (FBs) and permanent bed planting (PBs), contrasted with conventional tillage (CT) in Bangladesh’s main maize producing agro-ecological zones (AEZs). Trials were conducted in 184 farmers’ fields in Bangladesh’s northwestern districts with coarse-textured soils (Rangpur and Rajshahi in AEZs 3 and 11, respectively) and in one eastern district with fine-textured soils (Comilla in AEZ 19). Trials spanned the 2009–2010 to 2012–2013 rabi seasons. Significant TCE effects on grain yield were observed in AEZs 3 and 11, but not in AEZ 19. Compared to CT, grain yields under FBs, PBs and ST were significantly higher in AEZ 3, and also under FBs and PBs in AEZ 11. Production cost was 7.8% lower, while net profit and benefit-to-cost ratios for the alternative TCE options were 13.7 and 20% greater than CT, although data were inconsistent in AEZ 19. Across AEZs, total energy inputs were significantly higher for CT (30.3.5 × 10 3 to 33.8 × 10 3 MJ ha −1 ) compared to alternative options (28.3 × 10 3 to 32.7 × 10 3 MJ ha −1 ). Permanent beds required the lowest diesel energy compared to CT. Similarly, energy use efficiency (EUE) was significantly higher for PBs and ST compared to CT in AEZ 3 (7.17–8.08 MJ MJ −1 ) and for PBs and FBs in AEZ 11 (8.55–10.26 MJ MJ −1 ). Among all options, PBs, FBs and ST provided greater benefits in terms of increased yield and profits, increased EUE, and reduced economic risks in AEZs 3 and 11, but less so in AEZ 19. Poor performance in the latter region was due mainly to poorly-drained low- to medium-low land types that delayed maize planting and impeded optimal establishment. Further efforts are needed to untangle the determinants of spatially variable performance to refine recommendation domains for TCE options for maize in South Asia. [ABSTRACT FROM AUTHOR]

Rice–maize (R–M) systems are rapidly expanding in South Asia and Bangladesh due to higher yield and profit potential from rabi (winter) maize, its reduced water requirement compared to rice–rice systems, and increasing demand from poultry and fish feed industries. The current practice of growing puddled transplanted rice and maize with conventional, repeated tillage degrades soil structure, delays maize planting, and reduces its yield potential, increasing energy and labour requirements, ultimately leading to high production costs. Conservation agriculture (CA)-based tillage and crop establishment options such as strip or reduced tillage, and raised beds, may hold potential to increase yield, reduce crop establishment costs, and increase income of the farmers. The objective of this study was to evaluate the productivity and profitability of R–M systems under CA-based tillage and crop establishment options across a gradient of 69 farmers’ fields in Northwest Bangladesh. We evaluated four tillage and crop establishment options: reduced tillage; strip tillage; fresh beds; and permanent beds. Conventional-tilled (puddled) transplanted rice on flat followed by conventional-tilled maize on flat was included as a current practice. ANOVA for adjusted 4-year pooled mean revealed no significant treatment effects for yield and economic analysis parameters for rice ( P ≥ 0.05), but they were significant for maize and the R–M system ( P ≤ 0.05). Rice yields across tillage and establishment treatments over four years ranged from 4.6 to 4.9 t ha −1 while maize and R–M system yields ranged, respectively, from 7.8 and 12.5 t ha −1 under conventional tillage to 9.0 and 13.8 t ha −1 on permanent beds. Compared to conventional tillage, the average maize and system yield across fresh beds, reduced tillage, and strip tillage, was greater by 9.1% and 6.1%, respectively. Maize production costs ranged from US $922 ha −1 with fresh beds to US $1,027 ha −1 for conventional tillage. Maize net returns and benefit cost ratio (BCR), however, ranged, respectively, from $945 ha −1 and 1.9 under conventional tillage to $1350 ha −1 and 2.4 under permanent beds. We conclude that while CA-based tillage and establishment options may not have significant yield advantage over conventional tillage in rice, they have significant advantages in terms of reduced production cost and labour use, and increased net returns. For maize as well as for R–M system, while most options can provide yield benefits similar to conventional tillage, permanent beds exhibit a significant advantage (yield, net returns, etc.) over conventional tillage. Profitability was consistently greatest and significantly different ( P ≤ 0.001) under permanent raised beds compared to all other treatments. Considering our assessment of the profitability distributions and risk analysis, we conclude that both rice and maize planted sequentially on permanent beds and strip tillage can result in higher net income and BCR compared to conventional tillage practice. [ABSTRACT FROM AUTHOR]

In May 2020, approximately four months into the COVID-19 pandemic, the journal's editorial team realized there was an opportunity to collect information from a diverse range of agricultural systems on how the pandemic was playing out and affecting the functioning of agricultural systems worldwide. The objective of the special issue was to rapidly collect information, analysis and perspectives from as many regions as possible on the initial impacts of the pandemic on global agricultural systems, The overall goal for the special issue was to develop a useful repository for this information as well as to use the journal's international reach to share this information with the agricultural systems research community and journal readership. The editorial team put out a call for a special issue to capture the initial effects of the pandemic on the agricultural sector. We also recruited teams from eight global regions to write papers summarizing the impacts of the first waves of the pandemic in their area. The work of the regional teams and the broader research community resulted in eight regional summary papers, as well as thirty targeted research articles. In these papers, we find that COVID-19 and global pandemic mitigation measures have had significant and sometimes unexpected impacts on our agricultural systems via shocks to agricultural labour markets, trade and value chains. And, given the high degree of overlap between low income populations and subsistence agricultural production in many regions, we also document significant shocks to food security for these populations, and the high potential for long term losses in terms of human, natural, institutional and economic capital. While we also documented instances of agricultural system resilience capacities, they were not universally accessible. We see particular need to shore up vulnerable agricultural systems and populations most negatively affected by the pandemic and to mitigate pandemic-related losses to preserve other agricultural systems policy objectives, such as improving food security, or addressing climate change. Despite rapid development of vaccines, the pandemic continues to roll on as of the time of writing (early 2022). Only time will tell how the dynamics described in this Special Issue will play out in the coming years. Evidence of agricultural system resilience capacities provides some hopeful perspectives, but also highlights the need to boost these capacities across a wider cross section of agricultural systems and encourage agri-food systems transformation to prepare for more challenges ahead. [Display omitted] • 8 regional summaries, 30 research papers on agricultural systems responses to the initial waves of the pandemic • The Special Issue primarily highlights immediate impact of COVID-19 mitigation measures on agricultural systems • Emerging impacts include widespread impacts on food security for vulnerable populations engaged in agriculture • Additional impacts via disruptions to agricultural labour and trade, agricultural incomes and livelihoods • Evidence of resilience capacities within many agricultural systems to the pandemic, but not universal [ABSTRACT FROM AUTHOR]

Potassium (K) availability in soils is largely governed by their mineralogical composition. The extent of weathering of primary K-bearing minerals, the chemical pathways through which weathering takes place, as well as the dynamic equilibrium between various K fractions in soils are factors which determine different soil types of varying K-supplying capacity. The marked variability of K availability in soils in South Asia needs to be taken into account when formulating K-management strategies in intensive cereal-based systems in response to K application. Evidence from long-term fertilizer experiments in rice-rice (R-R) or rice-wheat (R-W) systems strongly indicates significant yield responses to K application and negative K balances where K application is either omitted or applied suboptimally. However, K-fertilizer recommendations in South Asia are generalized over large areas while farmers neglect K application to crops and remove crop residues from fields. These practices may strongly affect yield and soil K-fertility status in the emerging rice-maize (R-M) systems in different locations of South Asia. The dry-matter yield of the R-M system is usually much higher than that of the R-R or R-W system causing high withdrawal of nutrients from the soil. The current review assesses various K forms and K availability in diverse soil types of South Asia supporting rice-based systems. Aspects considered include: long-term crop yield and its response to added nutrients, K balance for intensive rice-based systems, and the role of crop residues in supplying K to crops. Emerging data from either completed or on-going experiments on the R-M systems in India and Bangladesh have revealed very high system productivity and variable responses and agronomic K-use efficiency of maize and rice. Potassium responses of maize are extremely high and variable for soils in Bangladesh. Finally, a plant-based strategy for field-specific nutrient management is presented and the need for models and decision support systems for developing efficient K management of the R-M system is also discussed. [ABSTRACT FROM AUTHOR]

Field experiments were conducted at the Punjab Agricultural University, Ludhiana, India, during 2007-2008 to examine if nitrogen (N) rates and weed management practices using herbicides in combination with hand-weeding (HW) can improve crop competitiveness against weeds, and increase the yield, water productivity and profitability of direct-seeded rice (DSR). Increasing N application rate up to 150 kg ha-1 caused significant improvement in grain yield when the weeds were well controlled either by Pendimethalin + Bispyribac Na or by Pendimethalin + Bispyribac Na + 1 HW, respectively; however, under poor weed control condition (Pendimethalin + 1 HW), it resulted in a drastic reduction in yield. The highest net returns ($1083) and water productivity (0.60 kg m-3) were observed for N application of 150 kg ha-1 and weeds were controlled with Pendimethain + Bispyribac Na + 1 HW. We suggest that Pendimethalin + Bispyribac Na + 1 HW is the best integrated weed management strategy to control weeds, and to increase yield, water productivity, and profitability. We propose that the simulation modelling tool be utilized in future for evaluating options for improving sustainable N and weed management policies especially when crop, weeds, soil, weather and management data are available for calibration and validation of appropriate and existing simulation model of rice. [ABSTRACT FROM AUTHOR]

Smallholder farmers of the Eastern Indo-Gangetic Plains (EIGP) of South Asia rely mainly on cereal-based cropping systems to meet the food and nutritional demand and support their livelihood. Yet the productivity of the major cereals - rice, wheat, and maize - in the region are far lower than their potential. Nutrient management plays a crucial role in improving cereal yields and economic return, and continued improvement in nutrient management practices and their on-farm implementation is required to develop locally relevant solutions that are site-specific, easy-to-develop and geared towards system resilience. The objective of the study was to conduct the comparative assessment of three nutrient management strategies for the three major cereals considering productivity, profitability and nutrient use efficiencies (NUE); estimate their potential yields and yield gaps; and explain the causes of yield variability across farmer-participatory on-farm trials in the EIGP of Nepal. We compared three nutrient management strategies (farmer's fertilizer practice- FP, government recommendation -GR, and Nutrient Expert®- NE-based recommendation), in 600 on-farm trials. We used the NE DSS tool, APSIM – a cropping system simulation model, and machine learning (ML) approaches (Linear Mixed Effect model -LME; and Random Forest model - RF) for the three cereals using data from those trials. The NE and APSIM were chosen due to simplicity in use and their wider evaluation and application in fertilizer recommendation yield prediction; RF was chosen due to its robustness in predictive ability and identifying and ranking factors determining yield or other variables of interest. The NE-based fertilizer recommendations for maize, wheat and rice increased yield by about 3.5, 1.4, and 1.3 t ha−1 respectively, increased profits, and improved NUE over FP or GR. The risk analysis showed that at a given probability level, NE always resulted in higher yields of all cereals than GR or FP. APSIM identified 25th June as optimum transplanting date for rice and 10th December as optimum sowing date for maize and wheat and simulated long-term average potential yield of 7–7.5, 5–5.5 and 13–13.3 t ha−1 respectively for rice, wheat and maize. There were larger yield gaps between PY and FP (2.6–8.5 t ha−1) than PY and NE (2.0–3.7 t ha−1) across crops and villages. The LME model showed highly significant treatment and location effects for grain yield of all cereals. The point estimate of the difference for grain yield as estimated by Tukey's HSD test was highest for NE-FP and lowest for GR-FP for all crops. The RF model identified grain N uptake for rice and grain P and K uptakes for wheat and maize as most influential factors contributing to their grain yield under each nutrient management strategy. The NE-based nutrient management had significant effects over FP and GR leading to positive changes on yield and economic performance under varied growing environments. These findings based on novel tools and approaches have important policy implications for increasing food security and profits from the major cereals by refining or improving the GR or FP and increasing their NUE in Nepal. Studies with larger sample size across varied agro-climatic zones in the EIGP and much of South Asia would help policy makers consider DSS tools and ML approaches suitable for upscaling and large-scale adoption by smallholder farmers. [Display omitted] • Factors influencing the low and variable grain yields of rice, wheat, and maize in the eastern Gangetic Plains are not fully understood • Study assessed nutrient management options, estimation of yield potential and yield gaps, and causes of yield variability in 600 on-farm trials • APSIM Model estimated potential yield and yield gaps and identified optimum planting dates. • Random Forest identified nutrient uptake as important variable explaining yield variability. • Nutrient Expert® recommendation can increase yield, gross returns and nutrient use efficiency over farmers' practice and government recommendation. [ABSTRACT FROM AUTHOR]

The objective of this study was to understand the impacts of COVID-19 crisis in agriculture and food systems in Nepal and assess the effectiveness of measures to deal with this crisis. The study draws policy implications, especially for farming systems resilience and the achievement of SDGs 1 and 2. The findings are based on (i) three panel discussions over six months with policy makers and experts working at grassroots to understand and manage the crisis, (ii) key informants' interviews, and (iii) an extensive literature review. Results revealed that the lockdown and transport restrictions have had severe consequences, raising questions on the achievement of SDGs 1 and 2, especially in the already vulnerable regions dependent on food-aid. This crisis has also exposed the strengths and limitations of both subsistence and commercial farming systems in terms of resiliency, offering important lessons for policy makers. Traditional subsistence farming appears to be somewhat resilient, with a potential to contribute to key pillars of food security, especially access and stability, though with limited contributions to food availability because of low productivity. On the other hand, commercial farming - limited to the periphery of market centres, cities, and emerging towns and in the accessible areas - was more impacted due to the lack of resilient supply networks to reach even the local market. Lower resiliency of commercial farming was also evident because of its growing dependence on inputs (mainly seeds and fertilizer) on distant markets located in foreign countries. The observation of crisis over eight months unleashed by the pandemic clearly revealed that wage labourers, indigenous people, and women from marginalized groups and regions already vulnerable in food security and malnutrition suffered more due to COVID-19 as they lost both external support and the coping mechanisms. The findings have implications for policies to improve both subsistence and commercial farming systems – in particular the former by improving the productivity through quality inputs and by diversifying, promoting and protecting the indigenous food system, while the latter through sustainable intensification by building reliant supply network linking farming with markets and guarantying the supply of inputs. • Family-based subsistence farming systems were less affected than the market-based commercial farming systems. • Need for greater food self-sufficiency was realized because of ban on food export from other countries. • Lockdown had severe consequences on achievement of SDGs 1 and 2. • Absence of policies to support food production and food security during crises was exposed. [ABSTRACT FROM AUTHOR]

In South Asia's rice-based cropping systems, most farmers flood and repetitively till their fields before transplanting. This establishment method, commonly termed puddled transplanted rice (TPR), is costly. In addition, it is labor and energy intensive. To increase labor and energy efficiency in rice production, reduced or zero-tilled direct seeded rice (ZT-DSR) is commonly proposed as an alternative tillage and crop establishment (TCE) option. Effective management of weeds in ZT-DSR however remains a major challenge. We conducted a four-year experiment under a rice-maize rotation in Northwestern Bangladesh in the eastern Gangetic Plains to examine the performance of two TCE methods and three weed management regimes (WMR) on the diversity and competitiveness of weed communities in the rice phase of the rotation. The Shannon-Weiner Diversity Index, a measure of species diversity, was significantly greater under ZT-DSR than puddled TPR. It was also greater under no weed control (Weedy) and two manual weeding (MW) treatments compared to chemical herbicide with manual weeding (C + MW). In DSR Weedy plots, weed communities began shifting from grasses to sedges from the rotation's second year, while in the ZT-DSR and C + MW treatments, sedges were consistently predominant. In both puddled TPR Weedy and TPR C + MW treatments, broadleaves and grasses were dominant in the initial year, while sedges dominated in the final year. There were significant main effects of year (Y) and weed management regime (WMR), but not of TCE. Significant Y × TCE and TCE × WMR interaction effects on rice yield were also observed. Grain yields under ZT-DSR were similar to puddled TPR. ZT-DSR with one application of pre-emergence herbicide followed by one hand weeding at 28 days after establishment however resulted in significantly higher grain yield (5.34 t ha−1) compared the other weed management regimes. Future research should address methods to effectively manage weed community composition shifts in both ZT-DSR and TPR under rice-maize rotations utilizing integrated and low-cost strategies that can be readily applied by farmers in the eastern Gangetic Plains. • A 4-year trial examined tillage and crop establishment (TCE) effects on weeds and rice yield. • Zero-tilled direct seeded rice (ZT-DSR) yielded similarly as puddle transplanted rice (TPR). • TCE had a large influence on weed community composition over time. • Weed species diversity was greater with ZT-DSR than TPR. • Safe, low-cost integrated weed management options are needed for ZT-DSR. [ABSTRACT FROM AUTHOR]

Precision planting represents an opportunity for farmers to increase income. Seeders and associated seed meters are prerequisite to achieve optimal plant density. However, to assure seed meter performance in smallholder conditions, a comprehensive procedure is lacking. This study develops a methodology for mechanical maize meter evaluation that compares diverse meters in terms of seed singulation, seed damage, and spatial distribution. An experiment assessed 10 m, representing roller types, and inclined, vertical, and horizontal plates collected from various continents and representative of commonly used devices by smallholders. A conveyer-belt setup allowed for seed distribution analysis and the influence of vibration and topography on the seed singulation was determined. Results revealed that a rotational velocity of 20 revolutions per minute (RPM) was optimum for most meters, while all complied with the norm NMX-O-168-SCFI-2009 in terms of seed damage. Independent of the singulation mechanism, devices with the ability to adjust to seed size performed better. The Fitarelli horizontal plate, followed by the BARI-9 inclined plate meter, are considered 'best-bet' performers. Although, considering absolute efficiency, two inclined plate devices worked at near-perfect performance with large seeds. Our study develops a low-cost methodology, easily replicated and implemented, and provides a baseline for continued research on seed meter evaluation. [ABSTRACT FROM AUTHOR]

The rice-wheat system (RWS), managed over 10.5 Mha in the Indo-Gangetic Plains of India suffers from production fatigue caused by declining soil organic matter, multi-nutrient deficiencies and diminishing factor productivity. We, therefore, conducted a long-term field experiment (1998–1999 to 2017–2018) in Modipuram, India to study the effect of continuous use of farmyard manure (FYM) as an organic fertilizer (OF), mineral fertilizers applied alone (RDF) and their combination (IPNS), as well as the inclusion of forage berseem (IPNS+B) or forage cowpea (IPNS+C) on crop yield, soil health and profits. The long-term yield trends were positive (p < 0.05) in all treatments except the control (unfertilized) in rice, and the control and RDF in wheat. Although the yields of rice, wheat and RWS were highest under IPNS treatments (IPNS, IPNS+B, IPNS+C), the maximum annual yield increase in rice (9.2%) and wheat (13.7%) was obtained under OF. A linear regression fitted to the yield data under different IPNS options revealed a highly significant (p < 0.001) annual yield increase in rice (5.1 to 6.6%) and wheat (6.8 to 7.7%) crops. Continuous rice-wheat cropping with RDF brought an increase in soil bulk density (Db) over the initial Db at different soil profile depths, more so at depths of 30–45 cm, but inclusion of forage cowpea or berseem in every third year (IPNS+B or C) helped to decrease Db, not only in surface (0–15 cm) but also in sub-surface (15–30 and 30–45 cm depth) soil. Whereas soil organic carbon (SOC) increased under OF, IPNS and IPNS + legume (B or C) treatments, it remained unaffected under RDF after 20 RW cycles. The inclusion of legumes along with IPNS not only helped to trap the NO3–N from soil layers below 45 cm but also increased its retention in the upper soil (0–15 cm depth). On the other hand, RDF had a higher NO3–N content in the lower layers (beyond 45 cm depth), indicating downward NO3–N leaching beyond the root zone. A build-up of Olsen-P was noticed under RDF at different time intervals. The soil exchangeable K and available S contents were maximal under OF and IPNS options, whereas a decline in DTPA extractable-Zn was recorded under OF. Overall, RWS economics revealed that OF treatment involved the maximum cost of cultivation (US$1174 ha−1) with the least economic net return (US$1211 ha−1). Conversely, IPNS + legume (B or C) had lowest cost of cultivation (US$707 to 765 ha−1) and a significantly higher (p < 0.05) net return (US$2233 to 2260 ha−1). The study, thus, underlines the superiority of IPNS over RDF or OF; the inclusion of legumes gives an added advantage in terms of production sustainability and soil health. Further studies involving IPNS ingredients other than FYM is needed to develop location-specific IPNS recommendations. [ABSTRACT FROM AUTHOR]

Meeting global demand of safe and healthy food for the ever-increasing population now and into the future is currently a crucial challenge. Increasing crop production by preserving environment and mitigating climate change should thus be the main goal of today's agriculture. Conventional farming is characterized by use of high-yielding varieties, irrigation water, chemical fertilizers and synthetic pesticides to increase yields. However, due to either over- or misuse of chemical fertilizers or pesticides in many agro-ecosystems, such farming is often blamed for land degradation and environmental pollution and for adversely affecting the health of humans, plants, animals and aquatic ecosystems. Of all inputs required for increased agricultural production, nutrients are considered to be the most important ones. Organic farming, with use of organic sources of nutrients, is proposed as a sustainable strategy for producing safe, healthy and cheaper food and for restoring soil fertility and mitigating climate change. However, there are several myths and controversies surrounding the use of organic versus inorganic sources of nutrients. The objectives of this paper are: (i) to clarify some of the myths or misconceptions about organic versus inorganic sources of nutrients and (ii) to propose alternative solutions to increase on-farm biomass production for use as organic inputs for improving soil fertility and increasing crop yields. Common myths identified by this review include that organic materials/fertilizers can: (i) supply all required macro- and micro-nutrients for plants; (ii) improve physical, chemical and microbiological properties of soils; (iii) be applied universally on all soils; (iv) always produce quality products; (v) be cheaper and affordable; and (vi) build-up of large amount of soil organic matter. Other related myths are: "legumes can use entire amount of N2 fixed from atmosphere" and "bio-fertilizers increase nutrient content of soil." Common myths regarding chemical fertilizers are that they: (i) are not easily available and affordable, (ii) degrade land, (iii) pollute environment and (iv) adversely affect health of humans, animals and agro-ecosystems. The review reveals that, except in some cases where higher yields (and higher profits) can be found from organic farming, their yields are generally 20–50% lower than that from conventional farming. The paper demonstrates that considering the current organic sources of nutrients in the developing countries, organic nutrients alone are not enough to increase crop yields to meet global food demand and that nutrients from inorganic and organic sources should preferably be applied at 75:25 ratio. The review identifies a new and alternative concept of Evergreen Agriculture (an extension of Agroforestry System), which has potential to supply organic nutrients in much higher amounts, improve on-farm soil fertility and meet nutrient demand of high-yielding crops, sequester carbon and mitigate greenhouse gas emissions, provide fodder for livestock and fuelwood for farmers and has potential to meet global food demand. Evergreen Agriculture has been widely adapted by tens of millions of farmers in several African countries and the review proposes for evaluation and scaling-up of such technology in Asian and Latin American countries too. [ABSTRACT FROM AUTHOR]

Intensive rice (Oryza sativa)-based cropping systems in south Asia provide much of the calorie and protein requirements of low to middle-income rural and urban populations. Intensive tillage practices demand more resources, damage soil quality, and reduce crop yields and profit margins. Crop diversification along with conservation agriculture (CA)-based management practices may reduce external input use, improve resource-use efficiency, and increase the productivity and profitability of intensive cropping systems. A field study was conducted on loamy soil in a sub-tropical climate in northern Bangladesh to evaluate the effects of three tillage options and six rice-based cropping sequences on grain, calorie, and protein yields and gross margins (GM) for different crops and cropping sequences. The three tillage options were: (1) conservation agriculture (CA) with all crops in sequences untilled, (2) alternating tillage (AT) with the monsoon season rice crop tilled but winter season crops untilled, and (3) conventional tillage (CT) with all crops in sequences tilled. The six cropping sequences were: rice-rice (R-R), rice-mung bean (Vigna radiata) (R-MB), rice-wheat (Triticum aestivum) (R-W), rice-maize (Zea mays) (R-M), rice-wheat-mung bean (R-W-MB), and rice-maize-mung bean (R-M-MB). Over three years of experimentation, the average monsoon rice yield was 8% lower for CA than CT, but the average winter crops yield was 13% higher for CA than CT. Systems rice equivalent yield (SREY) and systems calorie and protein yields were about 5%, 3% and 6%, respectively, higher under CA than CT; additionally, AT added approximately 1% more to these benefits. The systems productivity gain under CA and AT resulted in higher GM by 16% while reducing the labor and total production cost under CA than CT. The R-M rotation had higher SREY, calorie, protein yields, and GM by 24%, 26%, 66%, and 148%, respectively, than the predominantly practiced R-R rotation. The R-W-MB rotation had the highest SREY (30%) and second highest (118%) GM. Considering the combined effect of tillage and cropping system, CA with R-M rotation showed superior performance in terms of SREY, protein yield, and GM. The distribution of labor use and GM across rotations was grouped into four categories: R-W in low-low (low labor use and low GM), R-M in low-high (low labor use and high GM), R-W-MB and R-M-MB in high-high (high labor use and high GM) and R-R and R-MB in high-low (high labor use and low GM). In conclusion, CA performed better than CT in different winter crops and cropping systems but not in monsoon rice. Our results demonstrate the multiple benefits of partial and full CA-based tillage practices employed with appropriate crop diversification to achieve sustainable food security with greater calorie and protein intake while maximizing farm profitability of intensive rice-based rotational systems. • Rice-maize (R-M) outperformed over all other rice-based cropping systems considering yields and profits. • Conservation agriculture (CA) and alternate tillage (AT) outperformed than conventional tillage (CT). • R-M and rice-wheat-mungbean systems are more beneficial when layered with CA and AT. • Rice-rice system is more labor intensive and less profitable than other systems. • CA is good for winter crops and for cropping systems but not for rice but AT can be viable alternative option. [ABSTRACT FROM AUTHOR]

Nitrogen (N) in plants is generally diagnosed by a soil test and plant tissue analysis. However, such analyses are costly in terms of time and money and are not easily accessible by researchers and extension workers, let alone farmers. Alternative cost-effective methods are required for rapid analysis of the N status of crops and to guide N management in wheat. The objective of this study was to assess whether the SPAD values using a leaf chlorophyll meter could be used to apply N at the maximum tillering (MT) stage of irrigated spring wheat grown under light soils of South Asia. Experiments were conducted over two years under light soils at the Wheat Research Centre (WRC), Dinajpur, Bangladesh. Treatments were 80, 100 and 120 kg N ha-1, applied two-thirds as basal and one-third at the crown root initiation (CRI) stage along with additional 10, 20 and 30 kg N ha-1 (first year) and 0, 10, 20 and 30 kg N ha-1 (second year) at MT. Rates at MT were determined on the basis of SPAD values, which fell below the critical value of 37.5, recorded at 45 days after sowing (DAS). SPAD values recorded at 55 and 65 DAS were positively correlated with grain yield (GY), indicating that the application of extra N at MT influences wheat GY. Our results have two major implications: (i) SPAD values based on a leaf chlorophyll meter can be used for N application and (ii) extra 30 kg N ha-1 at MT is recommended for achieving maximum GY of irrigated spring wheat under the light soils of South Asia. [ABSTRACT FROM AUTHOR]

In South Asia, wheat is typically grown in favorable environments, although policies promoting intensification in Bangladesh's stress-prone coastal zone have resulted in expanded cultivation in this non-traditional area. Relatively little is known about how to best manage wheat in these unique environments. Research is thus needed to identify ‘best-bet’ entry points to optimize productivity, but classical parametric analyses offer limited applicability to elucidate the relative importance of the multiple factors and interactions that influence yield under such conditions. This problem is most evident in datasets derived from farmer-participatory research, where missing values and skewed data are common. This paper examines the predictive power of three non-parametric approaches, including linear mixed effects models (LMMs), and two binary recursive partitioning methods: classification and regression trees (CARTs) and Random Forests. We collected yield, crop management, and environmental observations from 422 wheat fields in the 2012–13 season, across six production environments spanning southern Bangladesh, where nutrient rates and genotypes were imposed, but management of other production factors varied from farmer to farmer. Fields were grouped into categories including early- and late-sowing, depending on crop establishment before or after December 15, respectively, and in combination, across both early- and late-sowing groups. For each of these groups, we investigated how each non-parametric analysis predicted the factors influencing yield. All three approaches identified nitrogen rate and environment as the most important factors, regardless of sowing category. CART also identified assemblages of high- and low-yielding environments, although those located in saline and warmer thermal zones were not necessarily the lowest yielding, indicating that farmers can optimize crop management to overcome these constraints. The number of days farmers sowed wheat before or after December 15, days to maturity, and the number of irrigations and weedings also influenced yield, though each method weighted these factors differently. LMMs also indicated a slight yield advantage when farmers used stress-tolerant genotypes, though CART and Random Forests did not. One-to-one plots for observed vs. predicted yields from LMMs and Random Forests showed better performance by the former than the latter, with smaller root mean square and mean absolute error for the combined, early- and late-sowing groups, respectively. While the LMMs were superior in this case, Random Forests may still prove useful in the classification and interpretation of farm survey data in which no treatment interventions have been administered. [ABSTRACT FROM AUTHOR]

Rising wheat demand in South Asia necessitates crop intensification to meet food security needs. Increased grain output can be achieved by bridging yield gaps on currently farmed land or by expanding cultivation to new land, though the latter entails environmental trade-offs and offers limited potential as most of South Asia's arable land is already cropped. Alternatively, opportunities for boosting production may exist where farmers can transition from single to double cropping and forgo dry season fallows – which are estimated at between 240,000 and 800,000 ha in southern Bangladesh – and establish a crop such as wheat following monsoon season rice. Southern Bangladesh's fallows result from prolonged post-monsoon soil saturation, soil salinity, and farmers’ low risk-bearing and investment capacity. In response, we assessed the potential to sow wheat on land that is seasonally fallow with approaches that optimize yields while reducing risk and rationalizing costs. Working with 64 farmers in eight production environments, we examined yield response to three genotypes, BG25 and BG27 (with salinity- and heat-tolerant traits) and BG21 (local check), across a gradient of sowing dates, grouped as ‘early’ (sown before 15 December) and ‘late’ (after 15 December), under 0, 100 and 133 and 0, 67 and 100 kg N ha −1 for early- and late-sowing groups, respectively. Across environments and genotypes, yield ranged from 2.11 to 4.77 t ha −1 (mean: 3.9 t ha −1 ) under early-sowing, and from 0.83 to 4.27 t ha −1 (mean: 2.74 t ha −1 ) under late-sowing. Wheat performance varied with environment (1.68–4.77 t ha −1 at 100 kg N ha −1 across sowing groups); the lowest yields found where early sowing was delayed and soil salinity levels were elevated. Small but significant ( P < 0.001) yield differences (0.22 t ha −1 ) were found between 100 and 133 kg N ha −1 for the early-sowing group, though no difference was found between 67 and 100 kg N ha −1 for late-sowing. Combining early- and late-sowing groups, significant environment × N rate and sowing-group × N rate interactions (both P < 0.001) for 100 kg N ha −1 indicated the importance of site-and time-specific N management in these stress-prone environments. Considering all cultivars and environments, ECa at sowing, flowering and grain filling negatively correlated with yield ( r = −0.50, −0.59 and −0.54, all P < 0.001). Correlations with ground water depth at flowering and grain filling were negative and significant, but less pronounced in the context of farmer-managed irrigation scheduling. Despite putative stress-tolerance traits in two of the three entries, no genotypic yield differences were found under early-sowing, though small differences (<0.19 t ha −1 ) were observed with late sowing. Agronomic fertilizer-N efficiency (AE-N) was consistently higher for 100 than 133 and 67 than 100 kg N ha −1 for early- and late-sowing. The marginal economic value of N application followed similar trends, indicating that rates of at most 100 and 67 kg N ha −1 are favorable for sowing before or after December 15th. Wheat can replace dry season fallows in Bangladesh's coastal delta, though site-specific management practices are needed to optimize yields while rationalizing investment costs to avoid the poverty traps that may ensue from poor management. [ABSTRACT FROM AUTHOR]