Maize Rice Research Articles

Optimization of extrusion process varibles for preparation of vitamin C enriched ready–to–eat product from maize–rice– aonla using response surface methodology

Response surface methodology (8.0.7.1) was employed to study the optimization of process variables of extrusion technology i.e. die temperature, Screw speed and feed moisture content. A ready to eat extruded food was developed by using a twin screw extruder. A nutritious ready to eat expanded product based on maize grits, rice flours and aonla was developed for school going children (6-16 years). Feed moisture content was found to have maximum influence on bulk density whereas the screw speed and die temperature had maximum influence on colour and expansion ratio of the product, respectively. Blends of maize grits, rice flours and aonla (80 : 10 : 10) were used as the ingredients for extrusion that would provide the vitamin C requirement of the targeted population with a minimum cost. Based on organoleptically evaluation, product extruded at processing conditions of 125°C die temperature, 310 screw rpm and 22 per cent (d.b) feed moisture content was found to be most acceptable quality extruded product.

Conservation agriculture based tillage and crop establishment options can maintain farmers’ yields and increase profits in South Asia's rice–maize systems: Evidence from Bangladesh

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 4.9tha−1 while maize and R–M system yields ranged, respectively, from 7.8 and 12.5tha−1 under conventional tillage to 9.0 and 13.8tha−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 $922ha−1 with fresh beds to US $1,027ha−1 for conventional tillage. Maize net returns and benefit cost ratio (BCR), however, ranged, respectively, from $945ha−1 and 1.9 under conventional tillage to $1350ha−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.

Uptake efficiency of 15N-urea in flooded and aerobic rice fields under semi-arid conditions

The sustainability of traditional rice (Oryza sativa L.) cultivation in many Asian countries is being questioned due to severe water shortage conditions, envisaging the need for development of water-saving rice production technologies. A 2-year-field study on a typic Haplustalf soil was conducted to compare traditional transplanted rice–maize system with water-saving aerobic rice–maize system, with an overall objective of investigating the fate of fertilizer nitrogen (N) using 15N-labeled urea. Results from the field experiments showed that the rice plants positively responded to N fertilizer application. The average fertilizer N recovery by rice crop over the 2 years in aerobic rice was 26 kg per 100 kg of applied fertilizer N in the main field and 21 kg per 100 kg of applied N in the microplot, while the recoveries were 41 and 32 kg ha−1 per 100 kg of applied N in traditionally cultivated rice under flooded conditions. The fraction of 15N that was found in soil after the harvest of rice crop ranged from 11.4 to 47.1 kg ha−1 in aerobic rice and 14.2–51.4 kg ha−1 in flooded rice. Average recovery of 15N fertilizer in maize after the first growing season was 3.3 %, and the corresponding recovery in soil was 19 %. An additional 1.3 % of the fertilizer was recovered by crops during the two subsequent seasons. This study indicates the need to develop management practices that improve N use efficiency in aerobic rice by reducing losses to improve yields and reduce N export to the environment.

Identifying irrigation and nitrogen best management practices for aerobic rice–maize cropping system for semi-arid tropics using CERES-rice and maize models

Research based development of best management options for aerobic rice–maize cropping systems must be developed to improve water and nitrogen use efficiency. The main objective of this study was to identify water saving rice production technology for rice grown in sandy loam soils in semi-arid conditions using the calibrated CERES-Rice and Maize models of the Decision Support System for Agro Technology Transfer (DSSAT). A two-year experiment with two different crop establishment methods viz., aerobic rice and flooded rice with four nitrogen rates followed by maize under zero tilled conditions was used to calibrate and evaluate DSSAT CERES-Rice and CERES-Maize models. The calibrated models were used to develop best management options for an aerobic rice–maize sequence which can produce similar yields with water savings relative to that of traditional flooded rice–maize system. The results showed that application of 180kgNha−1 in four splits and automatic irrigation with 40mm, when soil available water (ASW) in top 30cm fell below to 60% was the best management combination for aerobic rice, saving 41% of water while producing 96% of the yield attainable under flooded conditions. Similarly for maize, application of 120kgNha−1 and irrigation with 30mm of water at 40% ASW in the top 30cm soil was the most dominant management option. Further, application of 180kgNha−1 with rice followed by 120kgNha−1 in maize provided stable yield for both aerobic and flooded rice systems over time as simulated by the model. The results illustrate that DSSAT model is a useful tool for evaluating alternative management options aimed at maintaining yields and saving water in rice–maize systems in semi-arid regions.

Rainwater harvesting options for rice–maize cropping system in rainfed uplands through root-zone water balance simulation

A root-zone water balance model was used to simulate the soil moisture storage of maize (Zea mays L.) and rice (Oryza sativa L.) fields in rainfed uplands of eastern India. The simulation study revealed that short duration (95 days) rice fields in uplands remained under ponding condition for a period of 32 days during the entire growing season. Based on the ponding depth requirement in rice fields (50 mm), excess ponding was found for seven days only out of the 32 days of ponding. In contrast, the maize field under similar length of growing season (95 days) and topographic condition could produce harvestable runoff for 23 days. Furthermore, the rice crop was to remain under moisture stress for eight days during its mid-season stage, whereas the maize was found to be without stress during entire growing season. Before sowing of winter crops, the soil moisture in the seeding zone was determined to be depleted below germination soil moisture for 18 and 19 years out of 30 years of simulation in rice and maize fields, respectively. This implies that a second crop, following withdrawal of monsoon, is not possible without pre-sowing irrigation in three out of five years in rainfed uplands. Thus, complete substitution of rice by maize in uplands would create a better scope for rainwater harvesting. Alternatively, partial replacement of rice could be a viable option for meeting both rice demand of the people and harvesting of adequate rainwater for supplemental irrigation to crops in rainy and winter seasons.

Integration of conservation agriculture with best management practices for improving system performance of the rice–wheat rotation in the Eastern Indo-Gangetic Plains of India

Cereal production systems in the Eastern Indo-Gangetic Plains (E-IGP) are traditional, with low yield and low farm income, and they have largely missed out on the benefits of the Green Revolution. To enhance productivity, alleviate environmental and management constraints, and enhance farmers’ income in the rice–wheat cropping system of the E-IGP, new approaches that are more productive and sustainable need to be developed. Conservation agriculture (CA) together with best management practices (BMP) used in other parts of the IGP offer potential to be extended in the E-IGP. A study was conducted during 2009–2011 with the objective of evaluating a range of approaches for enhancing the productivity and economic returns of rice-wheat-based cropping systems in the E-IGP. Four scenarios (S) involving a range of crop and resource management practices with crop rotations (including legumesθ) were compared with one another, of which Scenario 1 represented farmers practice. The lowest yields of wheat (2.78–3.07tha−1) and rice (4.38–6.52tha−1) were recorded with the current farmers’ practices (S1), consisting of intensive tillage (wet tillage or puddling in rice and dry tillage in wheat) followed by inefficient crop establishment practices (transplanting in rice and broadcasting in wheat) with complete removal of crop residues. Avoiding tillage in wheat (S2) and including mungbean increased the yields of wheat and the succeeding rice crop by 21–31% and 5–10%, respectively. The yields of wheat and rice increased further by 46–54% and by 10–24%, respectively, with the inclusion of more CA components (S3). In S4, which was designed to include higher cropping intensity and diversification (potato and maize–rice–cowpea rotation) with CA components, 144–163% higher rice equivalent system productivity was attained. Irrigation water productivity in the winter season increased by 39–48% in S2, by 72–84% in S3, and by 137–138% in S4 when compared to S1 while in the rainy season it increased by 14–18% in S2, by 46–56% in S3, and by 71–88% in S4. S4 had the highest net returns ($2855–4193ha−1), followed by S3 ($1883–3246ha−1). However, the system’s highest benefit–cost ratio was recorded with S3 due to its lower cost of crop cultivation. The results of this study showed that there is enormous untapped potential to improve overall system performance through the adoption of CA in integration with BMP in the intensive system of the E-IGP of India.

Soil respiration, labile carbon pools, and enzyme activities as affected by tillage practices in a tropical rice–maize–cowpea cropping system

In order to identify the viable option of tillage practices in rice-maize-cowpea cropping system that could cut down soil carbon dioxide (CO2) emission, sustain grain yield, and maintain better soil quality in tropical low land rice ecology soil respiration in terms of CO2 emission, labile carbon (C) pools, water-stable aggregate C fractions, and enzymatic activities were investigated in a sandy clay loam soil. Soil respiration is the major pathway of gaseous C efflux from terrestrial systems and acts as an important index of ecosystem functioning. The CO2-C emissions were quantified in between plants and rows throughout the year in rice-maize-cowpea cropping sequence both under conventional tillage (CT) and minimum tillage (MT) practices along with soil moisture and temperature. The CO2-C emissions, as a whole, were 24% higher in between plants than in rows, and were in the range of 23.4-78.1, 37.1-128.1, and 28.6-101.2mgm(-2)h(-1) under CT and 10.7-60.3, 17.3-99.1, and 17.2-79.1mgm(-2)h(-1) under MT in rice, maize, and cowpea, respectively. The CO2-C emission was found highest under maize (44%) followed by rice (33%) and cowpea (23%) irrespective of CT and MT practices. In CT system, the CO2-C emission increased significantly by 37.1% with respect to MT on cumulative annual basis including fallow. The CO2-C emission per unit yield was at par in rice and cowpea signifying the beneficial effect of MT in maintaining soil quality and reduction of CO2 emission. The microbial biomass C (MBC), readily mineralizable C (RMC), water-soluble C (WSC), and permanganate-oxidizable C (PMOC) were 19.4, 20.4, 39.5, and 15.1% higher under MT than CT. The C contents in soil aggregate fraction were significantly higher in MT than CT. Soil enzymatic activities like, dehydrogenase, fluorescein diacetate, and β-glucosidase were significantly higher by 13.8, 15.4, and 27.4% under MT compared to CT. The soil labile C pools, enzymatic activities, and heterotrophic microbial populations were in the order of maize > cowpea > rice, irrespective of the tillage treatments. Environmental sustainability point of view, minimum tillage practices in rice-maize-cowpea cropping system in tropical low land soil could be adopted to minimize CO2-C emission, sustain yield, and maintain soil health.

System productivity, nutrient use efficiency and apparent nutrient balance in rice-based cropping systems

A 2-year field experiment was conducted to assess system productivity, nutrient use efficiency and apparent balances of phosphorus (P) and potassium (K) in diversified rice-based cropping systems at Gazipur, Bangladesh. Four cropping systems: wheat–fallow–rice, maize–fallow–rice, potato–fallow–rice and mustard–fallow–rice in main plots and four nutrient combinations: NPK, NK, NP and PK in sub-plots were arranged in a split-plot design with three replications. Receiving the NPK treatment, all the component crops gave the highest yield, and omission of N from fertilizer package gave the lowest yield. The maize–rice system removed the highest amount of N (217 kg ha−1), P (41 kg ha−1) and K (227 kg ha−1) followed by wheat–rice, potato–rice and the least in mustard–rice system. The wheat–rice and maize–rice system showed negative K balance of –35.5 and –60.4 kg ha−1 in NPK treatment, while potato–rice system showed a positive K balance of 31.0 kg ha–1 with NPK treatment. The N, P and K uptake and apparent recovery by the test crops may be used for site-specific nutrient management. The K rates for fertilizer recommendation in wheat and maize in Indo-Gangetic plain need to be revised to take account for the negative K balance in soil.

Thermogravimetric Analysis and Kinetics on Reducing Low-Grade Manganese Dioxide Ore by Biomass

Nonisothermal thermogravimetric analysis (TGA) was applied to evaluate rice straw, sawdust, wheat stalk, maize straw, and bamboo to explore their potential for reduction of manganese dioxide ore. Results from the biomass pyrolysis experiments showed that wood-based biomass materials, such as sawdust and bamboo, could produce more reductive agents, while herb-based biomass materials, such as rice straw, wheat stalk, and maize straw, had lower reaction temperatures. The peak temperatures for biomass reduction tests were 20 K to 50 K (20 °C to 50 °C) higher compared with the pyrolysis tests, and a clear shoulder at around 523 K (250 °C) could be observed. The effects of heating rate, biomass/manganese dioxide ore ratio, and different components of biomass were also investigated. An independent parallel first-order reaction kinetic model was used to calculate the values of activation energy and frequency factor for biomass pyrolysis and reduction of manganese dioxide ore. For better understanding the reduction process, kinetic parameters of independent behavior of manganese dioxide ore were also calculated by simple mathematical treatment. Finally, the isokinetic temperature Ti and the rate constant k0 for reduction of manganese oxide ore by reductive volatiles of biomass were derived according to the Arrhenius equation, which were determined to be 603 K (330 °C) and 108.99 min−1, respectively.

Potassium management in rice–maize systems in South Asia

AbstractPotassium (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.

Organic matter fraction and pools of phosphorus as indicators of the impact of land use in the Amazonian periphery

The unsustainable use of the soil of the deforested area at the Amazonian border is one of the greatest threats to the rainforest. Among the causes of land degradation in the humid tropics are phosphorus depletion (P), the decrease of soil organic matter (SOM) and the loss of basic cations. The aim of this study was determine the effects of different land uses on the dynamics of soil organic matter and phosphorus, to determine whether and how changes in the P and SOM can be used to assess the degree of land degradation in the humid tropics and whether the use of ecological systems can lessen or mitigate this degradation. Five systems were chosen according to potential use in the region: pasture of 30 years; no-tillage with 5 years of rice–maize rotations; no-tillage in alley cropping systems of 10 years; a newly cleared area; and 20 years of undisturbed secondary forest. Each field was sampled in a “W” pattern, to collect the soil samples from the chosen systems, prior to the chemical analyses. The SOM was separated by physical soil fractionation. The soil P fractionation was performed. All of the soil samples showed a very low pH range. The potential acidity was high under the alley cropping system, with more intensive and continuous use. All of the more labile fractions of organic matter decreased with the continuous use of soil in the alley cropping system. Therefore under alley cropping, most of the P (approximately 95%) was found in an inorganic form, and approximately 60% was found in the less labile fractions. The pasture and secondary forest showed higher contents of the labile fractions of organic matter and organic P. Higher correlations of organic P were found with the silt and clay fractions of organic matter. The results indicate that the fractions of P and organic matter are important indicators to assess changes in the degree of land degradation in the humid tropics. These results indicate also that the intensive and continuous use of annual crops in the soils of the humid tropics must be considered as posing a high risk to the sustainability of the agrosystems, mainly because of the increase of the active and potential acidity, the decrease of the labile organic matter and the depletion of the pools of organic P, leading to land degradation.

Characteristics and management options for rice–maize systems in the Philippines

In the Philippines, maize (corn) is the second major cereal crop after rice. Around 0.12 million ha of maize are grown in rice–maize (R–M) systems, mostly situated in the lowlands, and the area of this system is growing fast. The objectives of this study were to describe the targeted cropping system, to test several management options that could help to optimize it and reduce the production risk, and to develop a simple nutrient balance as a sustainability indicator. For this, we conducted participatory on-farm trials in Pangasinan province, where about 33,600ha of yellow maize are grown, mostly in R–M systems. Combined grain yields of the system reached 14tha−1 in the first year and 21tha−1 in the second year, depending on the treatment. Yield differences were mostly due to climate-induced stresses in the first year and very favorable conditions in the second year. Varietal choice in rice was an option to reduce production losses by selecting the variety according to average field-specific characteristics (drought-prone, favorable, flood-prone). Balanced fertilizer applications reduced stress-dependent rice yield losses considerably, and helped to maximize grain yield in the favorable season. The rice fertilizer treatment without any application caused lower yields in the subsequent maize crop but the effect was not significant. No effects of field topography on soil characteristics or on grain yields of rice or maize were detected. The nutrient balance indicated the considerable danger of soil nutrient mining in this cropping system, which could aggravate possible trends of declining soil organic matter concentrations in R–M systems that have been shown in previous studies. We concluded that a combination of adjusted management components can reduce production risk and optimize system productivity. To maintain system productivity, it seems most promising to combine different management elements, including balanced NPK fertilizer rates with limited PK mining, recycling of waste products from residue use on the farm as much as possible, and only limited removal of residues from the fields.

Impact of Aerobic Rice Cultivation on Growth, Yield, and Water Productivity of Rice–Maize Rotation in Semiarid Tropics

Limited water availability is a major constraint for cultivation of rice (Oryza sativaL.) in the traditional flooded systems, particularly in the semiarid regions of the world. Aerobic rice cultivation provides feasible alternative to traditional rice production in these regions, allowing significant water savings. Field experiments were conducted at the ANGR University Agricultural Research Station, India during 2009–2010 and 2010–2011 to compare crop growth, yield, and water savings under aerobic rice–maize (R–M) and flooded R–M rotation systems. The effect of aerobic rice on the succeeding maize crop was also studied. The total amount of water applied (including rainfall) in the aerobic plots was 967 and 645 mm compared to 1546 and 1181 mm in flooded rice system, during 2009 and 2010, respectively. This resulted in 37 to 45% water savings with the aerobic method. The soil moisture in aerobic treatment was maintained in the –30 to –40 kPa range throughout the crop growth. The aerobic rice system produced significantly lower grain yields in 2009 and 2010, where differences between flooded and aerobic rice were 39 and 15.4%, respectively. The yield differences were attributed to the differences in spikelet number per panicle and grain weight. Significant increase in yields was recorded in both systems with increased N rates up to 120 kg ha−1. Significantly higher yields were obtained in no‐till maize grown subsequent to the aerobic rice than flooded rice, possibly due to residual soil N and improved soil physical conditions.

Effect of crop diversification in rice (Oryza sativa)–wheat (Triticum aestivum) cropping system on system productivity, economics and soil health

A field experiment comprised of treatments comprising 14 crop sequences were conducted to study the effect of crop diversification in rice (Oryza sativa)–wheat (Triticum aestivum) cropping system on system productivity, economics and soil health. The results revealed that overall productivity of the system in terms of system rice grain equivalent yield was noticed significantly highest in rice-potato-blackgram (28.88 tonnes/ha/yr) compared to rest of the cropping sequences, followed by rice–maize (cob) + veg. pea (1:2) – greengram cropping sequence (25.67 tonnes/ha/yr). In addition to that inclusion of legumes either as green manure crop or grain/fodder legume proved crucial in maintenance of soil bio-physico-chemical properties of the soil. Therefore, diversification of rice–wheat system under irrigated condition by inclusion of moong crop after potato or wheat could enhance the overall productivity and profitability of the farm, besides improving the soil sustainability on long term basis.

Application rate and composting method affect the immediate and residual manure fertilizer value in a maize–rice–rice–maize cropping sequence on a degraded soil in northern Vietnam

A field experiment was carried out in northern Vietnam to investigate the effects of adding different additives [rice (Oriza sativa L.) straw only, or rice straw with added lime, superphosphate (SSP), urea or a mixture of selected microorganism species] on nitrogen (N) losses and nutrient concentrations in manure composts. The composts and fresh manure were applied to a three-crop per year sequence (maize–rice–rice) on a degraded soil (Plinthic Acrisol/Plinthaquult) to investigate the effects of manure type on crop yield, N uptake and fertilizer value. Total N losses during composting with SSP were 20% of initial total N, while with other additives they were 30–35%. With SSP as a compost additive, 65–85% of the initial ammonium-N (NH4-N) in the manure remained in the compost compared with 25% for microorganisms and 30% for lime. Nitrogen uptake efficiency (NUE) of fresh manure was lower than that of composted manure when applied to maize (Zea mays L.), but higher when applied to rice (Oriza sativa L.). The NUE of compost with SSP was generally higher than that of compost with straw only and lime. The mineral fertilizer equivalent (MFE) of manure types for maize decreased in the order: manure composted with SSP > manure composted with straw only and fresh manure > manure composted with lime. For rice, the corresponding order was: fresh manure > manure composted with SSP/microorganisms/urea > manure composted with lime/with straw alone. The MFE was higher when 5 tons manure ha−1 were applied than when 10 tons manure ha−1 were applied throughout the crop sequence. The residual effect of composted manures (determined in a fourth crop, with no manure applied) was generally 50% higher than that of fresh manure after one year of manure and compost application. Thus, addition of SSP during composting improved the field fertilizer value of composted pig manure the most.

Evolution of the Genes Encoding Starch Synthase in Sorghum and Common Wheat

Starch synthases (SSs) play important roles in plant starch synthesis. Five enzymetic isoforms of starch synthases have been found in plant, some of isoforms have further diverged possibly via whole genome duplication events, which might result in two or three subclasses of the sequences in rice and maize. In this study, we found the retention of GBSS, SSII, and SSIII duplicators except for the SSIV duplicator in genomes of sorghum and wheat. The SSIV gene might have been lost in maize and sorghum genomes based on the synteny relationship among rice maize and sorghum. Expression analyses indicated that the SS duplicators were also diverged from the duplicators of SbGBSSI, SbSSIIIa in expression pattern, and SbSSIIa were expressed mainly in endosperm in sorghum, whereas SbGBSSII, SbSSIIb, and SbSSIIIb of sorghum, TaSSIIb and TaSSIIIb of common wheat, were expressed mainly in leaves. Our findings, in combination with previous studies, indicate that the SSIV duplicator should be not remained in all Gramineae species, while the expression of duplicated SS genes diverged similarly in the studied species.

Rice-maize systems of South Asia: current status, future prospects and research priorities for nutrient management

Rice (Oryza sativa L.) and maize (Zey mays) are grown in 3.5 million hectares (Mha) in Asia that includes 1.5 Mha in South Asia. These crops are grown in sequence on the same land in the same year either in double–or triple-crop systems to meet the rice demand of a rapidly expanding human population and maize demand of livestock and poultry. The objective of this review is to provide a comprehensive overview of the current state of technical knowledge on agro-ecosystems and adaptation, area and distribution, yield potential and yield gaps, and nutrient management for rice-maize (R-M) systems in South Asia. Rice-maize systems are emerging all around South Asia but in particular are developing quite rapidly in Bangladesh and South and North India. Yield potential of rice and maize, as estimated by ORYZA2000 and Hybrid Maize models, reaches up to 15 and 22 t ha-1, respectively. However, data from several environments in India reveal gaps between potential and attainable yields of maize of upto 100% and between attainable and actual yields of upto 25–50%. Nutrient demand of R-M system is high due to high nutrient removal by high-yielding maize. Nutrient balance studies for these highly–productive and nutrient-extractive systems are scarce in South Asia. The review outlines principles of nutrient management for R-M systems, and identifies development, refinement, and dissemination of the integrated plant nutrition system technologies based on site-specific nutrient management principles as priorities for future research to increase yield, profitability, and sustainability of R-M systems.

Cell wall phenylpropanoid-related gene expression in early maize recombinant inbred lines differing in parental alleles at a major lignin QTL position

Fifteen quantitative trait loci (QTL) for cell wall digestibility and lignin content were shown in the recombinant inbred line (RIL) progeny descended from the cross between F288 and F271, two early dent lines of contrasted cell wall digestibility. Among these QTL, those located in bin 6.06, respectively explained 20 and 40% of the phenotypic variation for lignin content and cell wall digestibility. Expression of genes related to cell wall and lignin biosynthesis was investigated with the “MaizeWall” macro-array in two RIL having favorable alleles for low lignin content and high cell wall digestibility, except in bin 6.06 where RIL39 and RIL99 had unfavorable and favorable alleles, respectively. In the lignin pathway, three PAL, 4CL1, ZmCCR1, COMT, and ZmCAD2 genes were under-expressed in RIL99 in comparison to RIL39. In addition, two cytochrome P450, ZmCHS, and ZmCHI1 genes were simultaneously under-expressed while F5H2 and two OMT ZRP4-like genes were over-expressed. However, none of these genes were mapped in bin 6.06. Based on maize–rice synteny and on Maize Genome Sequencing Project data, several putative candidate genes related to lignin content and lignified tissue patterning were found in the support interval of bin 6.06 QTL. These genes included one C3′H which is likely the missing constitutive gene of the maize lignin pathway. Three ZRP4-like OMT were also shown in the support interval of the QTL. However, their involvement in the lignin pathway has not yet been firmly established. Several regulation or transcription factors were also shown in the QTL support interval. Among them, MYB, zinc finger, bZIP, and COV1 genes belong to families with members involved in lignification regulation or in lignified tissue patterning. In addition, auxin response factors have been shown to be indirectly involved in plant lignification. Moreover, several genes encoding proteins of unknown function and genes annotated “retrotransposon-like” were also located in the QTL support interval. Current results are not conclusive on the candidate gene discovery, but strengthen the hypothesis that regulation genes are better candidates than genes involved in the monolignol pathway. Fine mapping, association genetics, and/or functional validation have to be considered for more definite conclusions.

Phenol Accumulation in a Young Humic Fraction following Anaerobic Decomposition of Rice Crop Residues

Soil phenols have been implicated as inhibitors of soil N cycling within many agroecosystems, including irrigated lowland rice (Oryza sativa L.). To quantify the effects of crop management on temporal patterns of phenol accumulation in lowland rice soils, we measured phenol concentrations in two humic fractions at two crop growth stages in each growing season during a 4‐yr field study at the International Rice Research Institute (Philippines). Samples were collected from two double‐crop rotations (continuous rice and rice–maize [Zea mays L.]) with two N fertilizer rates (0 and nonlimiting), and with either aerobic or anaerobic decomposition of incorporated crop residues. Phenols were determined by tetramethylammonium hydroxide thermochemolysis. Compared with the other field treatments, anaerobic decomposition of crop residues with continuous rice and nonlimiting rates of N fertilizer promoted a gradual increase in the relative enrichment of phenols in the mobile humic acid fraction during the 4 yr. The level of enrichment varied among phenol compounds, developing the fastest and becoming most pronounced with the smaller molecules of molecular weight 168 or less. Anaerobic decomposition had less effect on phenol enrichment for continuous rice cropping without N fertilizer. No phenol enrichment was found with anaerobic decomposition of rice residues in the rice–maize rotation. Our results are consistent with previous findings of inhibited mineralization of humic N with anaerobic decomposition, continuous rice, and nonlimiting rates of N fertilizer. Rotation of maize with rice or other techniques to ensure aerobic decomposition of crop residues may help mitigate or prevent phenol accumulation.

Inhibition of nitrogen mineralization in young humic fractions by anaerobic decomposition of rice crop residues

SummaryField observations indicate a long‐term decrease in crop uptake of N derived from soil organic matter under continuous production of irrigated lowland rice (Oryza sativa L.). Decreased availability has been associated with an accumulation of phenolic lignin residues in soil organic matter, which can chemically bind N. To evaluate the hypothesis that the decrease in N availability results primarily from anaerobic decomposition of incorporated crop residues, 15N‐labelled fertilizer was applied three times during one growing season in a field study that compared anaerobic decomposition with aerobic decomposition for annual rotations of rice (Oryza sativa L.)–rice and rice–maize (Zea mays L.). Contents of 15N and total N during the growing season were measured in humic fractions and total soil organic matter. Results indicated an inhibition of N mineralization for the rice–rice rotation with anaerobic decomposition of crop residues, both for 15N that was immobilized after application and for total N. The inhibition was strongest for 15N that was applied at planting. It became more evident as the season progressed and reached significant levels during mid‐season stages of plant growth when crop demand for N peaks. These results were clearest for a young, phenolic‐rich humic fraction that was active in 15N immobilization and remineralization. Comparable but less significant trends were evident for a more recalcitrant humic fraction and for soil organic matter. Trends in crop‐N uptake associated the combination of rice–rice rotation and anaerobic decomposition with inhibited uptake of soil organic N but uninhibited uptake of fertilizer N. Increased aeration of rice soils through aerobic decomposition of crop residues or crop rotation is a promising management technique for improving soil N supply in lowland rice cropping.