Physical And Mechanical Properties Of Nerica Paddy (Rice)

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                           CHAPTER ONE



After harvest, agro raw materials are normally handled, transported, dried, stored and further processed into food, feed and fiber.

In some basic post harvest activities, separation processes such as sorting, grading and cleaning are involved.

In mechanized operations, these post harvest processes are supposed to be carried out with machines and equipment. The engineering design and efficient operation of the post harvest processing machines and equipment require adequate knowledge of engineering properties of the bio-materials. Knowledge of engineering properties such as physical and mechanical properties constitute important and essential engineering data in the design of machines; storage structures; processes and controls as well as in the analysis and determination of the efficiency of machines, development of new consumer products of plants and animal origin and in the evaluation of the quality of food products. (Mohsenin,1986; Oluka, 1991; Oluka and Nwuba, 2001).


NERICA, also known as New Rice for Africa (NERICA) is a hybrid of the local African rice variety with high disease resistant traits and the high yielding variety of Asia.  The rice is quite new to Africa and is currently being adopted and tried across the continent.

As a new product, there are on-going research studies on NERICA rice varieties. Studies on the engineering properties of the new rice variety are one of them.

Physical and Mechanical handling of the post harvest processing operation of NERICA require adequate knowledge of the physical and mechanical properties. This is the challenge of this study.

Knowledge of these properties will be valuable to Engineers, Food Scientists and Processors in designing of machines, storage structures, processes and controls as well as in the development of new products and quality assessment of food products.


The overall goal is to study the physical and mechanical properties of NERICA Paddy. The specific objectives include:

(i) To determine the physical properties of NERICA paddy such as shape, size, volume, density, specific gravity, sphericity and surface area.

(ii) To determine the mechanical properties of NERICA paddy such as rupture point, deformation, compressive strength, modulus of deformability, toughness, stiffness and the force at bio-yield point relevant to its milling and processing.


The information obtained are essential in the processing of rice paddy (NERICA) and prevention of mechanical damages during handling, processing and storage of the paddy. Equally, the knowledge of these properties will serve as a guide to designers of processing, storage and general handling equipments.


The scope of this study is limited to physical and mechanical properties of NERICA relevant to its milling and design of machines for its handling and further processing operations.  Only laboratory experimentation and measurements will be used as research procedures.




New Rice for Africa (“NERICA”) is among the 3000 species of rice family. It is obtained from the improved rice obtained by crossing two species of cultivated rice namely African rice (Oryza glaberrima Steud.) and the Asian rice (Oryza Sativa L.), which produced a progeny that combine the best trait of both parents. (Jones et al, 1997b and 1998a).

NERICA is produced through conventional cross breeding and it is not genetically modified rice. NERICA was developed by the West African Rice Development Association (WARDA) at the Africa Rice Center, Cotonou Benin Republic in the early 1990’s by a team of rice breeders led by Dr. Monty Patrick Jones. It is a new group of rice grown in rain fed upland ecology in Sub-Sahara Africa (SSA). NERICA can grow without irrigation, chemical fertilizers or pesticides. It responds better than traditional varieties to higher inputs. (Somado et al, 2008).

According to Jones et al (1997b and 1998a), NERICA seeds offer hope to millions of poor rice farmers and for countless others who struggle in urban squalor, spending most of their meager income on rice.


Brown Rice:It is un-polished rice which has been milled to remove the hull from the kernel but retained the rice bran layer and the germ; and these give it a nutty flavor and chewy texture.

Husked Rice: This is a rice from which the husk has been removed, still retaining the bran layers and most of the germs. Such a rice is sometimes referred to as bran rice, even though there are variations having them in red and white bran coats.

White Rice: It is also called raw or milled rice. It is a husked rice from which all or part of the bran and germ has been removed by milling.

Broken Rice: This can be husked or milled rice consisting of broken grains of less than ¾th size of the whole grain but not less than ¼th. (Michael and Ojha, 2005).


Paddy Rice: This is used to describe rice that has retained its husk after threshing. It is sometimes called rough rice (un-parboiled rice).

Rice Grain: It is referred to husked, milled or hand produced rice which does not contain any broken grains smaller than ¾ of the size of the whole kernel.

Rice Husk: This is the by-product from the milling of rice, consisting of the outermost covering of the rice kernels.

Rice Bran: It is a by-product from the milling of rice consisting of the outer layer of the kernels with part of germ.

Parboiled Rice: This is rice which has been specially processed by steaming or soaking in water, heating usually by steam and drying. It is milled rice processed from paddy or husked rice and it is known as boiled rice in some rice market. (Michael and Ojha, 2005).

Longitudinal Loading: This is loading the rice in upright position.

Lateral Loading: This is loading the rice laterally in lying  position.


NERICA Varieties are rice developed for Africans in order to reduce poverty, food shortage and a staple food security. A lot of studies have been carried out on the state of developments and achievements of NERICA varieties. (Somado et al, 2008).

Akintayo, et al (2010), reported that NERICA varieties, being an  inter- specific crossing of  two rice species (African and Asian) led to progenies that were not sterile, have favourable agronomic characteristics, significant widening genetic variation and allowing rice farmers to profit from  the Oryza. glaberrima gene pool.

They report that NERICA varieties have good agronomic performance and resistance to Africa’s harsh growth conditions, and especially short growth duration, much appreciated by farmers. They maintained that NERICA varieties resist pests, tolerate drought and grow in infertile soils better than most rice varieties.

Okello et al (2012) studied NERICA cultivation and its yield determinants based on upland rice system and stated that the response of NERICA rice yield to nitrogen is as high as 46kg/ha of paddy per 1kg/ha of nitrogen applied; 1kg/ha of increase in seeds applied increases rice yield by 8kg/ha and that continuous planting of NERICA on the field reduces its yield by 130kg/ha for every additional season of continuous planting.

Keijiro Otsuka and Sserunkuuma (2007) on assessing the impact of NERICA on income and poverty in the central and western Uganda, concluded that NERICA cultivation have achieved a sustainable reduction in poverty through increasing income of farmers in Sub-Sahara Africa by introducing a new profitable technology in traditional agriculture. This effect of NERICA can only be realized when its adoption is combined with the use of appropriate cropping patterns to maintain soil fertility.


Oni and Olaoye (2001), studied some physical and mechanical properties of sorghum, rice and millet at 17%, 13.3% and 10.2% (wb) and observed that the maximum loads for rupture and bio-yield points, 177.68N and 136.61N; 48,46N and 50.89N; and 7.08N and 10.08N  for sorghum, rice and millet respectively.

The results indicated that any force below the bio-yield force will not damage the cellular system of the grains and spoilage will not occur during threshing operation. Also, it is possible to simulate a threshing mechanism that may be applicable for threshing operation of these selected grain crops and generalized model can be developed to describe the energy requirements for the three selected grain crops and their corresponding responds at threshing.

Sadeghi and Hemmat (2005), working on the physical-mechanical properties of rough rice grain as affected by variety and moisture content reveals that the effect of variety and moisture content on most physical and mechanical properties were significant.

Kibar et al (2010), studied the effect of moisture content on physical and mechanical properties of Osmancik-97 rice. The study reveals that physical and mechanical properties of rice grain depend on its moisture content, stating that the axial dimensions of rice grain increased with moisture content and this is due to water absorption by the rice; the bulk density of rice grain decreased with increase in moisture content; the Static coefficient of friction for rice grain was higher on concrete surface followed by galvanized steel and wood; and poission ratio decreased with increase in moisture content.

Arana et al (2007) studied the physical and mechanical properties of Urucuia, Confianca and Jequitiba rice varieties and concluded that the bulk density of all the varieties increased to 51% and differ statistically among them; the specific gravity of the rice grains is not influence by the processing or varieties; the porosity of bulk rice grains is affected by the processing, the rough rice recorded higher values and milled rice lower; having a difference of 26%  and the external static and dynamic friction coefficients decreased with processing in all type of wall materials; and the static friction coefficient was affected more by varieties than the dynamic friction coefficient. Also, they reported that higher friction coefficient was recorded by the wood surface, while steel surface recorded lower friction coefficient.

Zareiforoush et al (2010) studied the effects of loading rate and internode positions  on mechanical properties of rice staws and  concluded that the loading rate do not have any effect on the shear strength, shearing energy and young’s modulus; but have effect on the bending strength. They reported that internode positions have significant effect on the shear strength, shearing energy and young’s modulus; but do not have significant effect on the bending strength.

Review of literature indicates that there is no study so far on the engineering properties of NERICA. This research gap is to be filled by this study.

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