Sustaining Rice Yield Research Articles

Application of additional dose of N could sustain rice yield and maintain plant nitrogen under elevated ozone (O3) and carbon dioxide (CO2) condition

IntroductionGlobal food security is challenged by the increasing levels of air pollutants like ozone (O3) through their impacts on crop productivity. The present study was conducted to quantify the interactive effect of elevated ozone (O3) and carbon dioxide (CO2), on different rice varieties in northern India.MethodsAn experiment was conducted in Genetic H field, Environment science, IARI for two consecutive years (2020 and 2021) during the kharif season, to quantify the impact of elevated O3 and CO2 interaction on productivity, and plant N in three rice varieties (Pusa basmati 1121, Nagina 22, IR64 Drt1) under different nitrogen (N) management practices. Rice crop was grown in Free Air Ozone-Carbon dioxide Enrichment rings (FAOCE) rings with two levels of O3 (elevated 60 ±10ppb and ambient) and two levels of CO2 (elevated, 550±25 ppm and ambient) concentration and their interaction with two N fertilizer treatments i.e., 100% RDN (recommended dose of N) and 125% RDN.Results and discussionElevated O3 significantly decreased physiological parameters like photosynthesis rate, stomatal conductance and transpiration rate of the crop. Grain yield reduced by 7.2-7.5%, in Pusa Basmati 1121 and from 6.9-9% in IR64 Drt1 varieties in elevated O3 treatment as compared to ambient treatment. Yield reduction in Nagina 22 variety was not significant in elevated O3 treatment. Elevated CO2 concentration of 550 ppm was able to fully compensate the yield loss in Nagina 22 variety and partially compensate (3.9-8.0%) in Pusa Basmati 1121 and IR64 Drt1 varieties. Grain N concentration in rice varieties decreased by 10.8-14.7% during first year and by 7.8-20.6% during second year in elevated O3 plus CO2 interaction treatment than ambient. Grain N uptake also decreased (13.2-17.1% in first year and 4.5-22.8% in second year) in elevated O3 plus CO2 interaction treatment as compared to ambient. Application of additional 25% of recommended dose of N improved grain N concentration, grain N uptake as well as available N of soil as compared to 100% RDN treatment in elevated O3 plus CO2 interaction treatment. Additional 25% N dose could help in sustaining rice productivity and quality under elevated O3 and CO2 condition.

Developing Early Morning Flowering Version of Rice Variety CO 51 to Mitigate the Heat-Induced Yield Loss

By 2050, the rice production needs to be increased by at least 50% in order to meet the growing food demands of the global population. Among various yield limiting factors, high temperature is fast becoming a major threat to sustain rice yields due to its increased frequency of occurrence and severity of stress events. The development of heat-resilient rice cultivars has been slow due to the lack of relevant donors for heat tolerance traits and limited information regarding the genetic basis of these component traits. The early morning flowering (EMF) trait, contributing to heat escape by promoting flowering/anthesis during cooler hours in the morning is demonstrated to offer protection against high-temperature-induced failure of pollination and fertilization. In this study, evaluation of CO 51, IR64 and IR64-qEMF3 (NIL of IR64 harboring QTL promoting EMF revealed that qEMF3 promoted early morning flowering in IR64-qEMF3 (1½ to 2 h earlier than IR64) and thereby reduced the sterility by about 8.15%. Attempts through marker-assisted backcross breeding led to development of advanced backcross progenies (NILs) of CO 51, harboring qEMF3. Evaluation of 88 BC3F2 progenies identified 19 progenies harboring qEMF3 under homozygous conditions. Evaluation of NILs of CO 51 harboring qEMF3 during summer 2019 revealed that the NILs exhibited early (7.30 a.m.) onset of anthesis by 1½ h and completed its peak anthesis well around cooler hours (9.30 a.m.) of the day and thereby recorded reduced spikelet sterility (7.8–9.0%) than their recurrent parent CO 51 (19.2%). The current study clearly demonstrated the efficacy of early morning flowering in the mitigation of yield losses under high-temperature conditions in a farmer preferred rice variety.

Designing low-input upland rice-based cropping systems with conservation agriculture for climate change adaptation: A six-year experiment in M’bé, Bouaké, Côte d’Ivoire

Climate change models predict an increase in climate variability in the future, with more rainfall extremes and greater risks, causing a negative impact on crops produced by smallholders in West Africa. Conservation Agriculture (CA) systems can be effective in mitigating yield loss in environments with increased weather risk. This study aimed to evaluate CA cropping systems that can minimize both economic and climatic risks under erratic climatic conditions in West Africa. We tested upland rice-based CA systems and conventional systems with tillage (CT), in rotation with maize in some of the cases, without and with fertilization, at different sowing windows in the Bouaké region, Côte d’Ivoire, from 2015 to 2020. Sowing in June showed in a higher rice yield (1183 kg ha -1 and 1370 kg ha -1 without and with fertilization, on average over the 2017–2020 period) than in March (521 kg ha -1 and 495 kg ha -1 without and with fertilization) or in July or August (335 kg ha -1 and 498 kg ha -1 without and with fertilization). During the first four years, rice yields tended to be lower under the CA systems than under the CT systems, especially when water availability was not a major constraint. However, after this transition period, and especially when water stress occurred, as in 2020, rice yields under CA systems (1835–2021 and 2147–2254 kg ha -1 without and with fertilization) were higher than under CT systems (1350 kg ha -1 and 1435 kg ha -1 without and with fertilization). CA systems having relatively longer duration for growing cover crops tended to produce higher upland rice yield grown in the subsequent season. In both CT and CA systems, the impact of fertilization on rice yield was small over the study period, and the mean rice yield increase due to fertilization was on average 451 kg ha -1 even when rice was sown in the summer season, resulting in negative economic return. These results indicate that whereas low-input CA upland rice-based systems together with optimizing sowing window for rice could be promising options for sustaining rice yield and mitigating yield loss in environments with increased weather risk, further research is needed for reducing transition period to CA systems in order to enhance their adoption by smallholder farmers. Desirable cover crops should be less labor-demanding, generate incomes from their products, and produce large biomass under erratic climatic conditions. • Conservation agriculture (CA) was compared to conventional tillage (CT) for 6 years. • In years 1–4, CT performed better than CA in favorable climatic years. • After 4 years, CA performed better than CT, especially in dry conditions. • Fertilization was not profitable in both CT and CA systems. • Associating cassava and stylo is a profitable option for soil regeneration.

Efficacy of organic nutrients on growth, yield and economics of rice (Oryza sativa)

A field experiment was conducted during the rainy (kharif) season of the year 2015 at the experimental site of Indian Institute of Technology, Roorkee to evaluate different soil nutrient management sources on growth, yield and economics of rice (Oryza sativa). The experiment was laid out in Randomized Block Design (RBD) with 8 treatments and 3 replications comprising different combinations of inorganic fertilizers and organic manures viz., T1-control, T2-recommended dose of chemical fertilizers (RDCF) @ 120:60:60, T3-FYM @ 20 t ha-1, T,-vermicompost (VC) @ 5 t ha-1, T5-50% FYM + 50% RDCF, T6-50% VC + 50% RDCF, T7-50?3 VC + 50% FYM and T8-25%VC + 25% FYM + 50% RDCF. Rice growth and development were observed better in the inorganic treated plot than the organic and INM treated plots. The response of FYM was observed better than vermicompost in respect of rice yield and yield attributes. The results suggested that complete organic incorporation may reduce rice yield, however, intigrated nutrient managment (INM) may be a better choice to sustain rice yield in the long term.

Nitrogen management can boost rice (Oryza sativa L.) production near aluminium smelter: A field study

Nitrogen (N) management is a key to sustain rice yield under submerged condition. Time and amount of N application boost rice production under adverse environmental situation. To test this hypothesis a field experiment was conducted at different villages in and around Hindustan Aluminium Company Ltd. (HINDALCO), Hirakud, Sambalpur, Odisha in the year 2015 and 2016. The rice ecosystems were selected on the basis of distance from the smelter plant. Different treatments were framed to test the hypothesis as T1-Farmers practice (60:30:30 kg N: P2 O5:K2O ha-1); T2- 75% recommended dose of fertilizer (RDF) of nitrogen(N) ; T3 -100% RDF of N; T4 -125% RDF of N; T5 -150% RDF of N. It was conducted in a randomized block design with four replications in the farmer's field. The test crop was rice cv.Tejaswinee. Growth parameters like plant height (cm), panicle length (cm) and number of effective tillers per hill were found to be highest in the plots where 125% RDF of N was applied. However the chlorophyll content(mg g-1 fresh)was estimated highest with 150 % RDF of N applied plots. The grain and straw yield (q ha-1) of rice were also observed highest with treatments receiving125% RDF of N.The rice ecosystems which are nearer to aluminium smelter plant were supposed to be affected with less yield as compared to far distance rice ecosystems. The grain quality parameterof rice like protein content (%) was also affected at smelter sites as compared to far distances. However with increasing the N level to 125 % RDF protein content was increased.

Sustained rice yields and decreased N runoff in a rice-wheat cropping system by replacing wheat with Chinese milk vetch and sharply reducing fertilizer use

Pollution from the paddy fields has posed a threat to surface water quality, and the reactive N in runoff has been recognized as the dominant contributor. In the rice-wheat systems of eastern China, replacing wheat (Triticum aestivum) with Chinese milk vetch (CMV) (Astragalus sinicus) is known to reduce total fertilizer N use and associated N losses during winter; however, the function of the rice-CMV system in controlling the N runoff loss was overlooked during the summer rice-growing season. Over 6 years, we monitored soil mineral N, plant N accumulation, rice grain yield, N agronomic efficiency (AEN), and N runoff in rice-CMV fertilizer N rate-response experiments and made comparisons with the conventional N inputs in rice-wheat rotation. Aboveground CMV residues added 65–116 kg N ha−1 yr−1; therefore, by adjusting the fertilizer time, the rice in this system required 44–56% less N fertilizer to produce rice yields equivalent to the 270 kg N ha−1 (district average, C270) used in the rice-wheat system. In all fertilizer N application treatments, 120 kg ha−1 seemed to be the threshold that ensured the soil N supply, the N accumulation at rice critical stages, and consequently, the current level rice yield. The corresponding runoff N averaged 9.3 kg ha−1 season−1, which was 51.8% less than that in C270 (19.3 kg ha−1 season−1). Cumulative N runoff (total N and NH4+-N) correlated strongly with fertilizer N input for any single year (sample size = 108, P < 0.01). Application of 30–120 kg fertilizer N ha−1 gave an equivalent AEN, which indicated that the integration of CMV and fertilizer N could increase the agronomic efficiency of N fertilizer applied to the rice. Rotating paddy rice with CMV instead of wheat, together with the suitable adjustment of N fertilizer, could sustain rice yield and gain the utmost environmental benefits from rice-based agroecosystems.

Effect of substituting nitrogen fertilizer with nitrogen-fixing cyanobacteria on yield in a double-rice cropping system in southern China

The efficient use of nitrogen fertilizer to increase rice production is essential for food security in China. However, the high-input of chemical nitrogen fertilizer has also resulted in soil N losses and environmental pollution. Here we investigated the possibility of using biofertilizer to reduce nitrogen fertilizer use via partial substitution of chemical nitrogen fertilizer (NF) with nitrogen-fixing cyanobacteria (NFC) in red soil. The effects of 100% NF (N10C0) and different substitution rates of NF with NFC (70%, 50%, 30%, and 0% NF plus 30%, 50%, 70%, and 100% N obtained through NFC, labeled as N7C3, N5C5, N3C7, and N0C10, respectively) on rice yield and soil properties were assessed in a double-rice system in greenhouse (six treatments) and field experiments (four treatments) from 2018 to 2019. The N10C0 and N7C3 treatments had no significant effect on grain and straw yields and the nutrient uptake in the greenhouse experiment. The higher substitution treatments could not sustain stable rice yields and the nutrient uptake in either greenhouse or field experiments, which indicated that 30% substitution was appropriate to sustain rice yields. For rice growth traits, higher substitution rates (70–100%) significantly decreased the number of tillers/plant and panicles/plant. In general, soil TN and TP contents in the 0–15 cm layer increased with increasing substitution rate during the early and late rice seasons. Compared to the N7C3 and N5C5 treatments, there were no significant differences in NH4+-N and NO3−-N contents under the N10C0 treatment. Compared to the application of NF as the sole nitrogen source, 30% substitution with NFC could result in monetary savings of approximately 5.77 US$ ha−1. Taken together, our findings demonstrate that substituting NF with an appropriate amount of NFC is beneficial for improving the productivity and sustainability of paddy fields under the double-rice cropping system.

Soil Organic Carbon in Sandy Paddy Fields of Northeast Thailand: A Review

Soil organic carbon (SOC) improvement has become a sustainable strategy for enhancing soil resilience and reducing greenhouse gas (GHG) emissions in the rice cropping system. For tropical soils, the SOC accumulation was limited by the unfavorable environment, likely the sandy soil area in Northeast (NE) Thailand. This review aims to quantify and understand SOC in sandy paddy fields of NE Thailand. The existing research gap for alternative management practices is also highlighted to increase ecological and agronomic values. We review previous studies to determine the factors affecting SOC dynamics in sandy paddy fields, in order to enhance SOC and sustain rice yields. High sand content, up to 50% sand, was found in 70.7% of the observations. SOC content has ranged from 0.34 to 31.2 g kg−1 for the past four decades in paddy rice soil of NE Thailand. The conventional and alternative practice managements were chosen based on either increasing rice crop yield or improving soil fertility. The lack of irrigation water during the mild dry season would physically affect carbon sequestration as the soil erosion accelerates. Meanwhile, soil chemical and microbial activity, which directly affect SOC accumulation, would be influenced by nutrient and crop residue management, including chemical fertilizer, manure and green manure, unburned rice straw, and biochar application. Increasing SOC content by 1 g kg−1 can increase rice yield by 302 kg ha−1. The predicted carbon saturation varied tremendously, from 4.1% to 140.6% (52% in average), indicating that the sandy soil in this region has the potential for greater SOC sequestration. Our review also suggests that broadening the research of rice production influenced by sandy soil is still required to implement adaptive management for sustainable agriculture and future food security.

QTL-seq reveals genomic regions associated with spikelet fertility in response to a high temperature in rice (Oryza sativa L.)

The QTL-seq approach was used to identify QTLs for spikelet fertility under heat stress in rice. QTLs were detected on chromosomes 1, 2 and 3. Rice is a staple food of more than half of the global population. Rice production is increasingly affected by extreme environmental fluctuations caused by climate change. Increasing temperatures that exceed the optimum temperature adversely affect rice growth and development, especially during reproductive stages. Heat stress during the reproductive stages has a large effect on spikelet fertility; hence, the yield decreases. To sustain rice yields under increasing temperatures, the development of rice varieties for heat tolerance is necessary. In this study, we applied the QTL-seq approach to rapidly identify QTLs for spikelet fertility under heat stress (air temperature of 40-45°C) based on two DNA pools, each consisting of 25 individual plants that exhibited a heat-tolerant or heat-sensitive phenotype from an F2 population of a cross between M9962 (heat tolerant) and Sinlek (heat sensitive). Three QTLs, qSF1, qSF2 and qSF3, were detected on chromosomes 1, 2 and 3, respectively, according to the highest contrasting SNP index between the two bulks. The QTLs identified in this study were found to overlap or were linked to QTLs previously identified in other crosses using conventional QTL mapping. A few highly abundant and anther-specific genes that contain nonsynonymous variants were identified within the QTLs and were proposed to be potential candidate genes. These genes could be targets in rice breeding programs for heat tolerance.

Rice yield and relationships to soil properties for production using overhead sprinkler irrigation without soil submergence

Production of irrigated rice (Oryza sativa L.) without conventional soil submergence may increase water use efficiency but risk a decline in rice yield. Spatial variability in rice yield and relationships among yield and soil properties were examined across a 3.3-ha experimental site after uniform crop management. The site was initially consolidated from small, previously puddled parcels of land into eight laser-leveled plots across a 2.1-m elevation gradient in the Philippines. Six crops of rice in rotation with three crops of mungbean (Vigna radiata (L.) R. Wilczek) were then grown from January 2012 to March 2015. The four rice crops in the dry season (crops 1, 2, 4, and 6) were irrigated using an overhead sprinkler system to maintain soil water potential greater than −10 kPa without soil submergence. Soil was puddled and flooded with irrigation for only rice crop 5 grown in the wet season. Mean rice yield with full fertilization was 6.1 Mg ha−1 for crop 2 but only 3.6 Mg ha−1 for crop 6. Yield for rice crop 6 ranged from 1.6 to 5.4 Mg ha−1 across 36 locations in the 3.3-ha site. Rice yield for crop 6 was inversely related to soil bulk density (r = −0.72 and −0.80, P < 0.001), log10 saturated hydraulic conductivity (Ksat) (r = −0.71, P < 0.001), and sand content (r = −0.63, P < 0.001). Yield was directly related to water-filled pore space of soil (r = 0.61, P < 0.001). Field locations with large downward water movement and the correspondingly most aerobic soil conditions were most prone to low rice yields and large yield decline. Rice yield was directly related to anaerobic N mineralization (r = 0.72, P < 0.001) and soil ammonium-N (r = 0.54, P < 0.001) at 16 days after transplanting and to indigenous N supply (r = 0.83, P < 0.001), as determined from rice yield without application of fertilizer N. These relationships suggested lower net N mineralization at locations with the most aerobic soil conditions, as determined by water-filled pore space. Rice yield was, however, not limited by insufficient fertilizer N. Anaerobic N mineralization and indigenous N supply were unrelated to optimum fertilizer N rate calculated from yield gain with fertilizer N, which was determined at 36 locations using paired plots with and without added N. The long rainy season and clayey soil at the site limited triple-cropping systems to two rice crops and only one non-rice crop per year. In such environments where crop rotation is not an option to prevent yield decline for rice grown without soil submergence, periodic soil submergence to increase anaerobic soil conditions would be required to sustain rice yield. Our study suggested that soil bulk density and Ksat, which can increase for successive rice crops grown without puddling and soil submergence, could serve as indicators of field locations prone to yield decline from factors other than water-deficit stress and requiring a period of soil submergence to sustain large rice yields.

Greenhouse gas emissions from rice field cultivation with drip irrigation and plastic film mulch

Ground cover rice production system is a promising technique with potentials to alleviate the effect of the increasing water-scarcity on rice production. Hence, finding appropriate management practices under this system is crucial for reducing global warming without yield loss. In this study, CH4 and N2O were quantified and contrasted in drip irrigation with plastic-film-mulch system (DP) and a continuous flooded rice cultivation system (CF) during two rice growing seasons of 2016 and 2017. The range of methane fluxes observed between irrigation regimes was (− 0.36 to 0.43 mg m−2 h−1) and (− 0.77 to 4.66 mg m−2 h−1) in 2016 and 2017 respectively. The cumulative CH4 emissions in 2017 under CF and DP were 16 times and 5 times higher than in 2016 respectively. DP reduced cumulative CH4 flux by 194% and 69% in 2016 and 2017 respectively compared to CF. Emissions of N2O were low and insignificant for both irrigation regimes. Grain yields were comparable between irrigation regimes with an insignificant reduction of 19% and 5% under DP in 2016 and 2017 respectively. The GWP of the 2-year average was 89% reduced under DP compared to CF. Our findings demonstrated that the DP mitigated GHGs while sustaining rice yield as a result of low nitrogen fertilization application and intermittent soil saturation level.

SOIL CHARACTERISTICS UNDER INTENSIFIED SHIFTING CULTIVATION FOR UPLAND RICE CULTIVATION IN UPLAND SABAL, SARAWAK, MALAYSIA

Shifting cultivation practices are regarded as the most important agricultural land-use in the marginal uplands of Sarawak for the livelihood of the rural communities. In response to various socio-economic consequences, previous practices on traditional form of shifting cultivation were altered into much sedentary farming practices. Soil productivity to sustain rice yield under current intensified forms of shifting cultivation should be of prime importance for food security among the local community at the marginal uplands of Sarawak. Therefore, this study was conducted to characterize soil properties influenced by the current intensified shifting cultivation practices at Sabal upland area, Sarawak. Along with the use of agrochemicals, shifting cultivation at Sabal area was conducted through single cultivation practices (10 to 15 years of fallow period and a cycle of rice cultivation) and multiple cultivation practices (5 to 7 years of fallow period and two cycles of rice cultivation). Before burning practices, soil pH was highly acidic (ranged from 4.28 to 4.72) in single cultivation sites; while multiple cultivation sites showed less acidic nature (soil pH ranged from 4.98 to 5.23) with relatively high secondary macronutrient contents, especially soil exchangeable Mg and Ca. No significant observation was found after burning practice in Total C and Total N of the soils at both sites. The level of soil exchangeable bases (K, Mg and Ca) and available P increased after the burning practices in single cultivation farmlands; while multiple cultivation sites showed lower to no increase in exchangeable bases and available P, partly attributed to the limited supply of nutrients from the aboveground biomass. After the harvesting of rice, soils at both sites tended to be more acidic and lower in macronutrient contents (K, Mg and Ca), primarily ascribable to crop uptake during the cultivation period. The average yield of rice in single cultivation sites and multiple cultivation sites were 721 kg/ha and 391 kg/ha, respectively. Our findings suggested that the usage of agrochemicals, particularly fertilizers in multiple cultivation sites are necessary for sustaining rice yield to restore the depleted macronutrients (especially K, Mg and Ca) after successive cultivation.

Evaluation of fertilizer and water management effect on rice performance and greenhouse gas intensity in different seasonal weather of tropical climate

Intensively double cropping rice increases greenhouse gas (GHG) emission in tropical countries, and hence, finding better management practices is imperative for reducing global warming potential (GWP), while sustaining rice yield. This study demonstrated an efficient fertilizer and water management practice targeting seasonal weather conditions effects on rice productivity, nitrogen use efficiency (NUE), GWP, and GHG intensity (GHGI). Two-season experiments were conducted with two pot-scale experiments using urea and urea+cattle manure (CM) under continuous flooding (CF) during the wet season (2013WS), and urea with/without CaSiO3 application under alternate wetting and drying (AWD) during the dry season (2014DS). In 2013WS, 120kgNha−1 of urea fertilizer resulted in lower CH4 emission and similar rice production compared to urea+CM. In 2014DS, CaSiO3 application showed no difference in yields and led to significant reduction of N2O emission, but increased CH4 emission and GWP. Due to significant increases in GHG emissions in urea+CM and CaSiO3 application, we compared a seasonal difference in a local rice cultivation to test two water management practices. CF was adopted during 2013WS while AWD was adopted during 2014DS. Greater grain yields and yield components and NUE were obtained in 2014DS than in 2013WS. Furthermore, higher grain yields contributed to similar values of GHGI although GWP of cumulative GHG emissions was increased in 2014DS. Thus, utilizing urea only application under AWD is a preferred practice to minimize GWP without yield decline for double cropping rice in tropical countries.

Evaluation of Soil Chemical Properties under Paddy Production System in Central Kenya: Soil Exchangeable Cations

&lt;p&gt;Lowland irrigated schemes contribute the most rice produced in Kenya. However, production is low and highly variable due to management problems. Production could be increased with appropriate soil management which requires that baseline fertility status of the soils and how they vary be known. This study examined the variability of selected soil chemical properties in the Mwea Irrigation Scheme in Central Kenya. Soil samples were collected from the top 0-15 cm depth in August 2013 and 2014 and analysed for pH, electrical conductivity (EC) and the exchangeable cations potassium (K&lt;sup&gt;+&lt;/sup&gt;), calcium (Ca&lt;sup&gt;2+&lt;/sup&gt;), magnesium (Mg&lt;sup&gt;2+&lt;/sup&gt;) and sodium (Na&lt;sup&gt;+&lt;/sup&gt;). Significant variability in soil EC as well as soil cation concentration was observed among units. Overall results showed soil pH ranged from 4.56 (very strongly acidic) to 8.05 (moderately alkaline). Soil EC varied from 0.17 to 1.52 dS m&lt;sup&gt;-1&lt;/sup&gt; with higher elevation areas recording lower values (&amp;lt; 0.50 dS m&lt;sup&gt;-1&lt;/sup&gt;) and lower elevation areas recording higher EC values (&amp;gt; 0.50 dS m&lt;sup&gt;-1&lt;/sup&gt;). On average, exchangeable Ca&lt;sup&gt;2+&lt;/sup&gt; was 38.17 cmol&lt;sub&gt;c&lt;/sub&gt; kg&lt;sup&gt;-1&lt;/sup&gt;, Mg&lt;sup&gt;2+&lt;/sup&gt; 23.80 cmol&lt;sub&gt;c&lt;/sub&gt; kg&lt;sup&gt;-1&lt;/sup&gt;, Na&lt;sup&gt;+&lt;/sup&gt; 1.24 cmol&lt;sub&gt;c&lt;/sub&gt; kg&lt;sup&gt;-1&lt;/sup&gt; and K&lt;sup&gt;+&lt;/sup&gt; 0.35 cmol&lt;sub&gt;c&lt;/sub&gt; kg&lt;sup&gt;-1&lt;/sup&gt;. The soil exchange complex was mainly dominated by Ca&lt;sup&gt;2+&lt;/sup&gt; and Mg&lt;sup&gt;2+&lt;/sup&gt; and cation concentration in the soil was in the order Ca&lt;sup&gt;2+&lt;/sup&gt; &amp;gt; Mg&lt;sup&gt;2+&lt;/sup&gt; &amp;gt; Na&lt;sup&gt;+&lt;/sup&gt; &amp;gt; K&lt;sup&gt;+&lt;/sup&gt;. Soil K is low and severe cation imbalances exist with regard to K&lt;sup&gt;+&lt;/sup&gt; and other cations thus making K&lt;sup&gt;+&lt;/sup&gt; deficient for plant uptake. Management practices and farming systems which enhance soil K status should be encouraged to help boost and sustain rice yield.&lt;/p&gt;

Improved nursery management further enhances the productivity of stress-tolerant rice varieties in coastal rainfed lowlands

The productivity of rice in most tropical coastal areas of Asia is low because of the predominance of several abiotic and biotic stresses, use of long duration traditional landraces or old varieties and suboptimal management practices. A combination of high-yielding, stress-tolerant rice varieties and good management practices is necessary to enhance the productivity of these areas. Suboptimal nursery management using traditional methods practiced in these areas often leads to a reduced plant population because of seedling mortality leading to poor yields. Nursery management practices that suit the new stress-tolerant varieties recently becoming available need to be developed to increase the productivity of rice. On-station and on-farm trials on nursery management were conducted using improved rice varieties to study the effect of seed density, nutrient management in the nursery, and seedling age at transplanting on grain yield. Lower seed density and application of balanced nutrients produced healthy and taller seedlings with high seedling vigor index (SVI) in the nursery and with subsequent significant increase in grain yield after transplanting in the main field. Combining inorganic and organic fertilizers in the seedbed (50–30–15kg N–P2O5–K2Oha–1+5tha–1 farm yard manures; FYM) enhanced seedling growth (dry weight, shoot and root length, number of green leaves, leaf area) and leaf nitrogen concentration. Forty-d-old seedlings produced significantly higher yield than 25-d-old seedlings. Transplanting older seedlings is important in systems without good water control, un-leveled fields, and soils affected by salt stress; and taller seedlings help avoid losses caused by floods. The highest benefit/cost ratios of 1.82, 1.72 and 1.91 were observed when transplanting 40-d-old seedlings using a seed density of 25gm−2 and with balanced nutrient application of 50–30–15kg N–P2O5–K2O+5t FYMha−1, respectively. In the on-farm trials, the yield advantages when using new stress-tolerant rice varieties Swarna-Sub1 and Amal-Mana with improved nursery management practices were 23% and 47%, in comparison with farmers’ nursery management and farmers’ variety, respectively. These cost-effective nursery management approaches have great potential for enhancing yield in stress-prone rainfed coastal areas and will help sustain rice yield while ensuring sustainability of the cropping system.

Carbon Pools and Associated Soil Enzymatic Activities as Influenced by Long-term Application of Fertilizers and Manure in Lowland Rice Soil

The effect of long-term (21 years) fertilizer application on soil carbon pools, its functional groups in humic acids and associated soil enzymatic activities was investigated in tropical flooded rice. The five treatments were non-fertilized control, nitrogen (N) (90 kg ha−1), farmyard manure (FYM) (10 t ha−1), NPK (90: 45: 45 kg ha−1:: N: P2O5: K2O) and FYM+NPK. On average, the microbial biomass carbon (MBC) content was significantly higher in FYM+NPK treatment as compared to control (by 30%), 100% N, 100% NPK + FYM treatments. The enzyme activities, viz. dehydrogenase, β-glucosidase, acid and alkaline phosphatase were found significantly higher under FYM + NPK treated plots compared with control by 107, 170, 133 and 190 per cent, respectively. The characteristic humic acid spectra revealed that FYM and NPK treated plot contains aromatic functional C groups, which have the potential to sequester C in the long run. Therefore, the combined application of FYM + NPK is a viable option for managing soil fertility as well as sustaining rice yield (4.1–5.7 t ha−1) in tropical flooded soils. The study is novel in the sense it describes soil carbon pools including labile active and passive pools in relation to soil functional microbial diversity under lowland flooded rice.

Comparison of Different Fertilizer Management Practices on Rice Growth and Yield in the Ashanti Region of Ghana

Nutrient management is critical in increasing and sustaining rice yield. A field experiment was conducted to examine the effects of inorganic fertilizer (IF), poultry manure (PM) and their combinations on rice yield and possible residual effects. A randomized complete block design with three replications was used and the trial was conducted on a Gleysol. In 2011 SPAD values for IF and PM/ IF combinations (except 2.0 t/ha PM + 22.5-15-15 kg N: P2O5: K2O/ha) were significantly higher in the sixth week onwards than PM. Number of panicles/plant and number of panicles m2 were significantly higher for 90-60-60 kg N: P2O5: K2O/ha and 2.0 t/ha PM + 22.5-15-15 kg N: P2O5: K2O/ha than 6.0 and 4.0 t/ha PM resulting in significantly higher grain yield. Grain yield of IF was similar to grain yield of PM/IF combinations. In 2012 the residual effects showed a significantly higher SPAD value for the 6.0 t/ha PM. Also 6.0 t/ha PM, 4.0 t/ha PM and 4.0 t/ha PM + 30 kg N/ha had significantly high number of panicles/plant and number of panicles/m2 than IF. Residual effect of PM applied at 4.0 t/ha and above gave significantly higher grain yield than IF. Mean grain yield for the three years showed that 4.0 t/ha PM + 30 kg N/ha and 2.0 t/ha PM + 22.5-15-15 kg N: P2O5: K2O/ha gave significantly higher yields than the other treatments. The results indicate that integrating IF and PM is a better option in increasing and sustaining rice production.

English

Fertility capability classification (FCC) system is a technical soil classification system focusing quantitatively on physical and chemical properties of soil important to soil fertility management.&nbsp; Lowland rice cultivation is a major activity in Cameroon, where demand for the commodity is increasing amidst increasing production constraints. This study was intended to classify lowland rice soils in major rice-growing areas into fertility capability classes, identify soil fertility limitations to increased lowland rice cultivation, and identify research areas needed to boost and sustain rice yields. Secondary data of selected soils characterized for morphological, physical and chemical properties was used. Soil fertility limitations characterizing lowland rice producing areas in Cameroon were: Fe- and Al-toxicities (a), low nutrient capital reserves (k), high leaching potential (e), and micronutrient deficiencies (Fe and Zn). The lowland soils were classified as:&nbsp;Lagk, Cagk, Laegk, Cbgm, Caeg, Lbg, Lgk, Cgv, LCg and Cgv,&nbsp;which reflect these limitations. A high potential exists to increase national rice production in Cameroon through research aimed at reducing the effects of Al and Fe toxicity, increasing nutrient capital reserves based on appropriate cultural and chemical techniques. &nbsp; Key words:&nbsp;Fertility capability classification, lowland rice, floodplains, Inland valleys, Cameroon.

Mitigating methane emissions from irrigated paddy fields by application of aerobically composted livestock manures in eastern China

AbstractLivestock manure heaps and wetland rice fields are major sources of CH4 emissions. A field experiment with an associated composting study were undertaken to investigate CH4 emissions during manure composting and subsequent land application on paddy. Over a 24‐day period in the composting experiment, CH4 emissions from stored manure was 17 times higher than that from composting manure, indicating that composting as an aerobic process was effective in mitigating CH4 emissions compared with manure storage, which is normally under an anaerobic environment. Stored and composted manures were subsequently applied as organic fertilizers in the field experiment. Compared with the non‐fertilized control treatment, stored and composted manures increased grain yields by 30% and 21%, respectively. During the full rice‐growing season, the cumulative CH4 emission was 15.8 g CH4/m2 with the application of composted manure, only one‐third of that from stored manure. CH4 emission per unit of grain yield was significantly decreased by composted manure, with a reduction of 56% from the control and 73% from stored manure. The results indicate that composted livestock manure in rice cultivation is a triple‐win option through sustaining rice yield, mitigating CH4 emissions and re‐utilizing livestock waste.

Methane Emission from Paddy Fields and its Mitigation Options on a Field Scale

Rice is one of the most important cereals, especially in Asian countries. Methane (CH4), one of the major greenhouse gases, is emitted from flooded paddy fields as a result of phenomena on various scales. This paper review studies on CH4 emission from paddy fields, paying special attention to mitigation options from the viewpoint of their feasibility on a field scale. Field management of rice paddies is primarily carried out to obtain suitable rice yields, but it also has physical, chemical, and biological effects on CH4 emission. Therefore, some management practices can be win-win options that sustain rice yield and mitigate CH4 emission. For example, appropriate water management for rice growth and yield is also effective in decreasing CH4 emission. Other practices, such as nitrogen fertilizer application and organic matter application can also have positive effects on rice yield and CH4 emission. Recent microbial studies have been revealing the ecology of methanogens and methanotrophs in paddy soils. Further studies on a microbial scale will offer additional clues to the mitigation of CH4 emission from paddy fields.