Lowland Paddy Research Articles

Effects of temperature and soil moisture on gross nitrification and denitrification rates of a Chinese lowland paddy field soil

Alternate wetting and drying (AWD) irrigation is widely adopted to save water in rice production. AWD practice shifts lowland paddy fields from being continuously anaerobic to being alternately anaerobic and aerobic, thus affecting nitrogen (N) transformations in paddy field soils. Using the barometric process separation technique, a large number of soil cores sampled from lowland paddy field soil profiles were measured for gross nitrification and denitrification rates under different temperature and soil moisture conditions. The gross nitrification and denitrification rates vary with rice growth stages and range between 1.18–30.8 and 0.65–13.54 mg N m−3 h−1, respectively. Results indicate that both gross nitrification and denitrification rates increased with the increase in temperature in all three studied soil layers. Gross nitrification rates significantly decrease with increasing soil moisture while denitrification rates increase, and different soil layers demonstrated different rates of variation to the increase in soil moisture. Gross nitrification rates in the cultivated horizon layer decreased more sharply with the increase in soil moisture. High soil water content is favorable to denitrification of all soil layers.

Improving Efficiency and TFP of Lowland Paddy Rice Farmers in Kwara State of Nigeria

Purpose: The pressure on land for agricultural purposes is on the rise and sustainable agriculture remains the panacea for herdsmen attack on arable crop farmers in the study area. The present research empirically measured and identified the factors that influenced efficiency and Total Factor Productivity (TFP) of lowland paddy rice farmers in Kwara State of Nigeria.Research Methodology: The study made use of cross-sectional data collected from 200 active farmers during the 2016 cropping season via Multi-stage sampling technique. Instrument used to elicit information from the active farmers was structured questionnaire complemented with interview schedule and the collected data were analyzed using descriptive and inferential statistics.Findings: The results proved that majority of the farmers were not smart farmers which is responsible for negative TFP in most of the Decision making units (DMUs) as evident from poor robust increase in output index. However, the study inferred that there remained more untapped potentials in paddy rice production in the studied area.Limitations: The scope of the research is limited to lowland rice farmers in Kwara State of Nigeria.Originality/Value: Therefore, it was recommended that Government and non-governmental organisations should formulate supportive policies targeting sustainability of rice production viz. proper allocation of farm resources and also welfare improvement of the resource poor farmers for cultivating rice crops in the studied area.

The Effect of Biofertilizer on The Diversity of N2O Reducing Bacteria in Paddy Fields of Sukabumi, Indonesia

<p class="IsiAbstrakInggris"><span lang="EN-GB">Some of the methanotrophic bacteria and N<sub>2</sub>O reducing bacteria have been proven to be able to support the plant growth and increase the productivity of paddy. However effect of the methanotrophic and N<sub>2</sub>O reducing bacteria application as a biofertilizer to indigenous N<sub>2</sub>O reducing bacteria is still not well known yet. The aim of this study was to analyze the diversity of N<sub>2</sub>O reducing bacteria in lowland paddy soil based on a </span><em><span lang="EN-GB">nosZ</span></em><span lang="EN-GB"> gene. Soil samples were taken from lowland paddy soils in Pelabuhan Ratu Sukabumi, West Java, Indonesia. There were two treatments for the paddy field soil, ie. biofertilizer-treated field 20% fertilizer (50 kg/ha) with the addition of biofertilizer and 100% fertilizer. PCR amplification of </span><em><span lang="EN-GB">nosZ </span></em><span lang="EN-GB">gene was successfully conducted using </span><em><span lang="EN-GB">nosZF</span></em><span lang="EN-GB"> and </span><em><span lang="EN-GB">nosZR</span></em><span lang="EN-GB"> primer pair. Denaturing Gradient Gel Electrophoresis (DGGE) process was conducted at 150 V for 5.5h. There were three differences </span><em><span lang="EN-GB">nosZ</span></em><span lang="EN-GB"> bands were sequenced. The phylogenetic analysis showed that they were close to uncultured bacteria. Microbial diversity in the biofertilizer-treated field was higher than that of in the 100% fertilizer-treated field. The biofertilizer treatment has higher in microbial diversity than that of applied non-biofertilizer paddy fields. This research might have impact in the application of biofertilizers due to the emission of N<sub>2</sub>O as a green house gas from paddy fields farming activity. The biofertilizer has great potential application in sustainable environmental friendly agriculture systems.</span></p>

Water regimes and ecosystem in lowland paddy field: a case study in Awlegama, Kurunegala, Sri Lanka

Paddy fields are manmade ecosystems. These fields undergo three water regimes namely, aquatic, semi aquatic and terrestrial within a cultivation season. Accordingly, the ecosystem also changes. In addition, agronomic practices can affect biodiversity and the overall ecology. A study was conducted to assess the water regime and respective ecosystem so that ecosystem can be enhanced as an adaptation for climate variability in paddy cultivation. The study was conducted in a command area of Bayawa minor irrigation system located in Awlegama Agrarian service division in Kurunegala District, Sri Lanka. Six randomly selected locations in the field were used in the fauna survey at different growth stages in Yala season in 2015. A water management index (WMI) was developed to assess the water regime using physical factors of the field and social capacity of farmer. Results revealed that wet condition is expected in more than 69% of farmers since their WMI is more than 0.5. Water regime varied among head, middle and tail sections. Tail end of the command area has more reliability for water than the head and middle sections. The water fluctuation leads to higher biodiversity. The initial water regime and crop growth stages have provided more habitats for the both terrestrial and aquatic invertebrates.The abundance of aquatic invertebrates were significantly (p= 0.01) varied over the five growth stages anddragonflies’ diversity was varied temporarily with respect to the species richness.Alternative wetting and drying have created more favorable habitats for aquatic fauna to increase the biodiversity of the fields. Increase of biodiversity promotes naturally enemies/predators for pests while aquatic fauna improve the nutrient availability in the fields. Therefore, water management in the fields could be used to enhance biodiversity in the rice field to achieve sustainable paddy cultivation.

Estimating nitrogen and phosphorus losses from lowland paddy rice fields during cropping seasons and its application for life cycle assessment

Estimating nitrogen and phosphorus losses into water bodies is crucial for evaluating the environmental impacts of rice cultivation. In this study, published data (N = 80) were used to estimate the total nitrogen (TN) and total phosphorus (TP) that could be lost through leaching and runoff during cropping seasons, taking into account factors that influence these losses. According to second-order Akaike's Information Criterion (AICc, one of the model selection methods), a model with soil temperature, TN input, inflow water, the incorporation of rice straw residue, puddling, and the use of slow-release fertilizer (P < 0.05) was chosen to estimate TN losses. A model with soil temperature, no application of phosphate fertilizer, medium- and coarse-textured soils (P < 0.05) and inflow water was chosen to estimate TP losses. The root mean square error was reduced by 34.5% for TN and by 21.8% for TP when these models were used compared to when the average proportions of outflowing nutrients were used (e.g., 17.0% for TN and 7.3% for TP in this study). The multiple regression model, taking into account site-specific conditions, was proven to be a readily available method to obtain knowledge of nutrient loading. Once process-based models are readily available, they will improve the estimates of eutrophication potential in life cycle assessments. Further improvement of the method is required, especially for the winter fallow period.

Breeding for submergence tolerance in rice (Oryza sativa L.) and its management for flash flood in rainfed low land area: A review

For rainfed low land paddy ecosystems which is supposed to withstand the sudden rise of water level for short period of time i.e. up to two weeks has been considered as the submergence tolerant. Proper screening and evaluation method are very important for cost effective and economic breeding procedures that will benefits the farmers. The agro morphological characters which are responsible for submergence tolerance; character association and path coefficient analysis will be very much useful to select them for further assessment. Hybrid rice will be another approach which could mitigate the flash flood constraints. Proper understanding of anatomical characters such as aerenchyma formation and changes of diameter of aerenchyma of root, shoot and leaf will be very much important for submergence tolerance if it is linked with genetic factors. Biochemical manipulation of different plant hormone such as gibberellic acid, abscisic acid and ethylene; enzyme like alcohol dehydrogenase synthesis; chlorophyll content and non structural carbohydrate content of shoot has significant role for enhancement of survival during underwater growth. Plant extracts or herbal crude product in the form of dry and wet treatments along with proper growth nutrients will be a holistic approach for sustainable and integrated agriculture and will be a tool for crop improvement in future breeding programme for submergence tolerance in rice.

Effect of biofertilizer on the diversity of nitrogen-fixing bacteria and total bacterial community in lowland paddy fields in Sukabumi West Java, Indonesia

Effect of biofertilizer on the diversity of nitrogen-fixing bacteria and total bacterial community in lowland paddy fields in Sukabumi West Java, Indonesia

Slow pyrolyzed biochars from crop residues for soil metal(loid) immobilization and microbial community abundance in contaminated agricultural soils

This study evaluated the feasibility of using biochars produced from three types of crop residues for immobilizing Pb and As and their effects on the abundance of microbial community in contaminated lowland paddy (P-soil) and upland (U-soil) agricultural soils. Biochars were produced from umbrella tree [Maesopsis eminii] wood bark [WB], cocopeat [CP], and palm kernel shell [PKS] at 500 °C by slow pyrolysis at a heating rate of 10 °C min−1. Soils were incubated with 5% (w w−1) biochars at 25 °C and 70% water holding capacity for 45 d. The biochar effects on metal immobilization were evaluated by sequential extraction of the treated soil, and the microbial community was determined by microbial fatty acid profiles and dehydrogenase activity. The addition of WB caused the largest decrease in Pb in the exchangeable fraction (P-soil: 77.7%, U-soil: 91.5%), followed by CP (P-soil: 67.1%, U-soil: 81.1%) and PKS (P-soil: 9.1%, U-soil: 20.0%) compared to that by the control. In contrast, the additions of WB and CP increased the exchangeable As in U-soil by 84.6% and 14.8%, respectively. Alkalinity and high phosphorous content of biochars might be attributed to the Pb immobilization and As mobilization, respectively. The silicon content in biochars is also an influencing factor in increasing the As mobility. However, no considerable effects of biochars on the microbial community abundance and dehydrogenase activity were found in both soils.

Metagenomic assessment of methane production-oxidation and nitrogen metabolism of long term manured systems in lowland rice paddy

Biochemical pathways of methanogenesis and methanotrophy coupled with carbon (C)-nitrogen (N) metabolism were studied in long term (13years) manured systems in lowland rice paddy through metagenomics approach. Manured systems included in this study were, control (exclusion of application of any manure), farm yard manure (FYM, @5Mgha−1yr−1) and green manuring (GM with Sesbania aculeata). Metagenomic sequence data revealed the dominance of C decomposing bacterial communities' like Proteobacteria, Planctomycetes, Actinobacteria, Firmicutes, Acidobacteria, in manure amended soils as compared to control. Diversities for assimilatory and dissimilatory N-fixing microorganisms at phylum level were found higher under GM as compared to rest. Two genera responsible for methanogenesis, viz. Methanolobus and Methanotorris were absent in manured systems as compared to control. The acetoclastic and serine pathway was found as the predominant pathway for methanogenesis and methanotrophy, respectively, in tropical lowland rice paddy. Abundance reads of enzymes were in the range of 254–445 in the acetoclastic methanogenesis pathway. On the other hand, these were varied from 165 to 216 in serine pathway of methanotrophy. Lowland paddy soil exhibited higher functional and structural diversities in manured systems as compared to unamended control in respect to labile C pools and CH4 production. Methane (CH4) emission was 31% higher in FYM system than GM. However, nitrous oxide (N2O) emission was found 25% higher in GM as compared to FYM. As a whole, bacterial diversities were higher under FYM system in tropical lowland rice paddy as compared to GM and unamended systems.

Robust optimal model for sustainable joint production of green tea and paddy rice in Japanese agricultural watersheds

In Japanese hilly agricultural watersheds, green tea is a profitable crop, whereas paddy rice cannot endure without subsidies. Environmentally, green tea plantations are the highest nitrate pollutant emitters to water bodies, whereas paddy fields are the most significant nitrogen sinks. This study investigates the effectiveness of diverting nitrate-contaminated drainage water from upland tea fields to the lowland paddy fields, in terms of reduction of downstream pollution and rice production cost, using the robust optimal model. The model optimally maximises diversions to reduce nitrate pollution to the adjacent rivers, and is environment risk averse to possible malfunctioning denitrification processes in the respective paddy fields. The application shows increased diversions to paddy fields during the rice growing season, thereby facilitating rice plants to have optimal access to substantial amounts of nitrogen nutrients and water. Thus, the robust optimal model has the potential to support sustainable joint production of the two crops.

Synthetic Aperture Radar (SAR)-based paddy rice monitoring system: Development and application in key rice producing areas in Tropical Asia

Reliable and regular rice information is essential part of many countries’ national accounting process but the existing system may not be sufficient to meet the information demand in the context of food security and policy. Synthetic Aperture Radar (SAR) imagery is highly suitable for detecting lowland paddy rice, especially in tropical region where pervasive cloud cover in the rainy seasons limits the use of optical imagery. This study uses multi-temporal X-band and C-band SAR imagery, automated image processing, rule-based classification and field observations to classify rice in multiple locations across Tropical Asia and assimilate the information into ORYZA Crop Growth Simulation model (CGSM) to generate high resolution yield maps. The resulting cultivated rice area maps had classification accuracies above 85% and yield estimates were within 81-93% agreement against district level reported yields. The study sites capture much of the diversity in water management, crop establishment and rice maturity durations and the study demonstrates the feasibility of rice detection, yield monitoring, and damage assessment in case of climate disaster at national and supra-national scales using multi-temporal SAR imagery combined with CGSM and automated methods.

Utilizing rainfall and alternate wetting and drying irrigation for high water productivity in irrigated lowland paddy rice in southern Taiwan

Taiwan’s average annual rainfall is high compared to other countries around the world; however, it is considered a country with great demand for water resources. Rainfall along with alternate wetting and drying irrigation is proposed to minimize water demand and maximize water productivity for lowland paddy rice cultivation in southern Taiwan. A field experiment was conducted to determine the most suitable ponded water depth for enhancing water saving in paddy rice irrigation. Different ponded water depths treatments (T2 cm, T3 cm, T4 cm and T5 cm) were applied weekly from transplanting to early heading using a complete randomized block design with four replications. The highest rainwater productivity (2.07 kg/m3) was achieved in T5 cm and the lowest in T2 cm (1.62 kg/m3). The highest total water productivity, (0.75 kg/m3) and irrigation water productivity (1.40 kg/m3) was achieved in T2 cm. The total amount of water saved in T4 cm, T3 cm and T2 cm was 20, 40, and 60%, respectively. Weekly application of T4 cm ponded water depth from transplanting to heading produced the lowest yield reduction (1.57%) and grain production loss (0.06 kg) having no significant impact on yield loss compared to T5 cm. Thus, we assert that the weekly application of T4 cm along with rainfall produced the best results for reducing lowland paddy rice irrigation water use and matching the required crop water.

Assessment of the suitability of temperature and relative humidity for rice cultivation in rainfed lowland paddy fields in Kurunegala district

Climatic suitability analysis is a prerequisite to achieve optimum utilization of the available resources in rainfed rice cultivation. Therefore, a study was conducted to assess the climatic factors and to map their suitability for rainfed paddy farming in Mahananeriya, Ibbagamuwa and Alawwa ASC regions representing dry, Intermediate and wet areas of Kurunegala District in Yala and Maha seasons using Geo-Informatics. Daily weather data of maximum temperature, minimum temperature, and relative humidity for 10 years were averaged on a weekly basis. The IDW interpolation technique was used to prepare thematic maps. The maximum temperature was grouped as 27 0 C - 32 0 C, 32 0 C - 35 0 C, and more than 35 0 C. The minimum temperature was grouped as less than 19 0 C and more than 19 0 C. Relative humidity was grouped into three classes as 60% - 80%, 80 % - 85% and more than 85%. The temperature maps and relative humidity maps were overlaid with the weighted sum technique giving weights as 0.75 and 0.25 respectively to produce suitability maps for rice cultivation on weekly basis throughout the year. Results show that minimum temperature is not in the critical level for rice cultivation within Kurunegala District throughout the year. Maximum temperature is optimum (27 0 C - 32 0 C) for rice cultivation in all three ASC regions during Maha season and in Ibbagamuwa and Alawwa ASCs during Yala season. Relative humidity in all three ASCs is more than 85% during Maha season and in between 80 % and 85 % during Yala season. Considering temperature and relative humidity, whole rainfed paddy lands in Ibbagamuwa and Alawwa ASCs are highly suitable for rice cultivation in the Yala season. Rainfed paddy lands in all three ASCs are in suitable category in terms of the suitability of temperature and relative humidity during Maha season. Spatial variations of the suitability of the interactive outcome of the maximum temperature and relative humidity appear among Mahananeriya, Ibbagamuwa and Alawwa ASC regions representing Dry (DL1b), Intermediate (IL1a) and Wet (WL3) zones in Kurunegala District. Intra regional spatial variations are very rare. Temporal variations among two seasons of Yala and Maha and the intra variations within the seasons also evidence. Date of seed sowing or crop establishment should be aligned according to the suitability levels matching with the flowering and grain filling stages of rice.

Erodibility status of soils under different land uses in West Khasi hills of Meghalaya

The effect of land use on soil erodibility parameters were studied in four villages, viz ., Nongstoin, Kynshi, Umyiap and Maweit in West Khasi Hills district, Meghalaya, under four land uses, viz ., lowland paddy, potato, forest and Jhum land, in each village. The textural class of the soils varied from silt loam to clay with dominance of clay loam texture. Dispersion ratio and erosion index were recorded to be usually higher than the threshold limits. A highly significant and negative relationship of erosion index with clay, silt + clay and highly significant and positive relationship with sand and dispersion ratio were observed. The increase in erosion index with increase in dispersion ratio indicated the susceptibility of these soils to water erosion. Proper soil and water conservation measures need to be adopted to protect the soils from further degradation.

Compensatory mechanisms of litter decomposition under alternating moisture regimes in tropical rice fields

A conversion from permanently flooded rice cropping systems to crop rotations that include non-flooded upland crops is heavily promoted in tropical regions to meet the challenges of sustainable food production while reducing water consumption and trace gas emissions. Shorter periods of flooding and manipulation of fertilizer inputs affect belowground community composition, biomass and functioning. However, there have been no previous studies of how such shifts in rice field management might affect soil biota and decomposition. Our objective was to examine how crop diversification, which demands different moisture regimes and nitrogen inputs, influences belowground invertebrate assemblages and their contribution to the decomposition of crop residues.We conducted a litterbag experiment in lowland paddy fields at the experimental field sites of the DFG-ICON project (Laguna, the Philippines) that were either continuously flooded, had seasonally alternating wet and dry periods, or were continuously dry. Additionally, subplot treatments within these crop rotations included different N fertilizer management practices. At a total of 36 plots we used litterbags with two different mesh sizes to assess decomposition with and without fauna over a period of 72days. Furthermore, we sampled soil microfauna and mesofauna in both the wet (rainy) and dry seasons.Although we found no correlation between faunal abundance and the contribution by invertebrates to rice straw decomposition, we found that soil water content was the decisive factor determining the activity of decomposer invertebrates as well as the composition and abundance of the soil fauna in fields with alternating cropping regimes. The impact of invertebrates on rice straw decomposition was higher under anaerobic than aerobic soil conditions which compensated for reduced microbial decay rates during periods of flooding. In contrast, microbial decomposition rates were higher under aerobic conditions, whereas invertebrates had no apparent effects on the mass loss of rice straw despite their higher abundance in dry fields. Our results demonstrate that invertebrates are essential for the effective decay of rice straw residues under flooded soil conditions, and therefore play an important role in supplying nutrients to flooded rice.

The effectiveness of methanotrophic bacteria and Ochrobactrum anthropi to reduce CH4 and N2O emissions and to promote paddy growth in lowland paddy fields

The effectiveness of methanotrophic bacteria and Ochrobactrum anthropi to reduce CH4 and N2O emissions and to promote paddy growth in lowland paddy fields

Changing local land systems: Implications of a Chinese rubber plantation in Nambak District, Lao PDR

This paper investigates the direct and cascading land system consequences of a Chinese company's land acquisition for rubber cultivation in northern Laos. Transnational land acquisitions are increasingly acknowledged as an important driver of direct land use conversion with implications for local land‐based livelihoods. The paper presents an empirical case study of the village of Na Nhang Neua in Nambak District, Luang Prabang Province, using a mixed methods approach to investigate the positive and negative implications for household agricultural strategies, income generation and food security. Combining the conceptual lenses of land systems and livelihood approaches, this paper demonstrates how the land use system has changed substantially because of the establishment of the rubber plantation by the company, notably in the linkages between livestock rearing, upland shifting cultivation and lowland paddy rice cultivation. The changes go beyond the immediate competition for land caused by the rubber plantation: a penalty scheme introduced by the rubber company for damage to rubber trees caused by browsing animals has led the villagers to abandon livestock rearing, causing a cascade of negative effects on the entire land use system, especially on soil fertility, rice yields and food production.

Organic matter content of a lowland paddy soil as affected by plant growth and urea fertilization

Soil organic matter (SOM) plays an important role in determining the land productivity. The effect of rice plant and inorganic fertilizer on the SOM content with time and soil depth in a lowland paddy field was investigated in this study. Two factors (fertilizer: with urea, without urea, and plant: with rice plant, without rice plant) with four treatment combinations were arranged in a randomized complete block design in a low land paddy field at a minor irrigation tank in Kurunagala district in Sri Lanka during the 2013/2014 Maha season. The soil samples were collected at 0 - 8, 8 - 16, 16 - 24 and 24 - 32 cm depths at 27, 43, 65 and 98 days after sowing (DAS) and SOM was measured using a standard method. Data were analyzed as a factorial design. The interaction between fertilizer and soil depth found to be significant (p=0.030). At the depth of 24 - 32 cm, the SOM content was significantly higher without urea than with urea. Fertilizer also showed a significant (p=0.024) interaction with DAS. The SOM content at 43 DAS was higher with urea than without urea while it is reverse at 65 DAS. Therefore, urea application has an influence on SOM content at different depths and time.

Variability of some important soil chemical properties of rainfed low land paddy fields and its effect on land suitability for rice cultivation

Available soil-phosphorus (P), exchangeable soil-potassium (K), soil pH and soil Electrical Conductivity (EC) affect rice production and are highly variable in nature mainly due to the variability in water availability. Therefore, experiments were conducted to find out the variability of some important soil chemical properties of rainfed lowland paddy fields and their effect on land suitability for rice cultivation in the Dry (Mahananeriya), Intermediate (Ibbagamuwa) and Wet (Alawwa) regions in the Kurunegala District of Sri Lanka. Randomly collected soil samples from the above three areas were analyzed for available soil-P, exchangeable soil-K, soil pH (1:2.5) and EC (1:5). Thematic maps for each parameter were prepared using Inverse Distance Weighted interpolation technique. Weighted sum technique was used to overlay maps to prepare the suitability map as Marginally Suitable, Moderately Suitable, Suitable and Highly Suitable. Results showed that the available soil-P and EC levels are preferable for rice cultivation in the rainfed lowland paddy fields in all three regions. Even with this situation, the potential productivity of the lands cannot be obtained due to variability of soil pH and exchangeable Potassium contents. Soil pH and the exchangeable soil Potassium in all rainfed paddy areas of Alawwa is far below the optimum levels for paddy cultivation. In terms of these soil chemical properties, 42% and 32% of rainfed paddy fields in Ibbagamuwa and Mahananeriya regions, respectively, are either highly suitable or suitable but 79% land extent of the rainfed paddy in Alawwa is marginally suitable for rice cultivation. Therefore, a blanket recommendation of remedial measures cannot be introduced to improve productivity of the rainfed paddy fields in these regions while site-specific remedial measures would help to overcome the problems of specific soil chemical properties. Tropical Agricultural Research Vol. 26 (3): 506 – 516 (2015)

Bulk soil properties as determinants of the compression strength of puddled lowland paddy soils in Sri Lanka

Soil strength/penetration resistance of lowland puddled soil is an important parameter for designing farm machinery. This study was aimed to estimate the overall penetration resistance of lowland puddled soils through the assessment of bulk soil parameters. Penetration resistance and bulk soil parameters including moisture content, bulk density, particle density, porosity, texture and organic matter content were measured under real field condition and evaluated to identify the suitable determinants to explain the variation of soil penetration resistance and their relationships. Results revealed that measured penetration resistance by Eijkelkamp hand penetrometer and bulk soil parameters except particle density, notably varied with weed controlling methods, depth of the soil and the time. Penetration resistance showed a significant relationship with bulk density (BD), moisture content (MC) and porosity (PO) at .05 α level as using the relationships 4017.87- 44.72 MC -1669.83 BD, 2115.65-44.18 PO and 3383.78-58.09 PO in 0 – 10 cm, 10 – 20 cm and 20 – 30 cm depths, respectively. Tropical Agricultural Research Vol. 26 (3): 561 – 568 (2015)