Rice: Background

Introduction

Rice (Oryza sativa) is a very important staple food in the world and feeds more than half of the entire population. Africa has become a big player in international rice markets importing a record 9 million tonnes in 2006 – accounting for more than 30 % of global imports. Approximately 40 % of the rice consumed in Africa is imported. Africa’s emergence as a big rice importer is explained by the fact that during the last decade rice has become the most rapidly growing food source in sub-Saharan Africa. Indeed, due to population growth, rising incomes and a shift in consumer preferences in favour of rice, especially in urban areas, the relative growth in demand for rice is faster in this region than anywhere in the world.

Rice is also becoming increasingly important for food security in some low income, food deficit countries in sub-Saharan Africa (SSA). About 100 million people depend on rice for their livelihoods. The demand in SSA far outstrips production, which in the last 30 years has increased by 70%, mainly because of the expanded area planted with rice. Only 30 % of the increase can be attributed to improved productivity.

Rice is cultivated in tropical and subtropical environments across a wide range of production systems. This includes production under different soil conditions, water management systems, levels of mechanization and levels of input applications. Rice production systems in Africa can be classified into rainfed upland, rainfed lowland (swamp), irrigated lowland and flood-prone (deep water) systems, based on the water availability for growth and the topography where rice is grown.

Irrigated rice system - In this system, rice is grown in bounded fields in lowlands where supplemental irrigation is necessary in addition to rainfall. Due to the possibility to irrigate, the rice crop can be grown during both the dry and wet seasons.
Rainfed lowland rice system - In this system, rice is grown in bounded fields in lowlands where the main source of water is rainfall. Due to heavy reliance on rain, too much water (floods) or too little water (drought) are potential limitations in this system. Nonetheless, this is the most dominant rice production system in Africa. Rice yields in rainfed lowlands depend on the degree of water control and vary from 1 to 3 tonnes per hectare. With improved water control and soil fertility management, rice yields may increase rapidly in these systems that are inherently much more stable than the upland areas.
Flood-prone rice system - In this system, deepwater and floating rice is grown in unbounded fields on the floodplains and deltas of rivers. Rice is sown or transplanted before the floodwaters rise and it flowers at about the time of maximum water depth.
Rainfed upland rice system - This is where rice is grown under normal soil moisture conditions, from low-lying valley bottoms to gentle and steep sloping lands. This is the dominant rice culture in West Africa, but also becoming popular in East and Central Africa. In this system, slash and burn is a common way of clearing land for upland rice production. Rice yields in upland systems average about 1 ton per hectare. Weed competition is the most important yield reducing factor followed by drought, blast, soil acidity and general soil infertility. Farmers traditionally manage these stresses through long periods of bush fallow. More recently, population growth has led to a dramatic reduction in fallow periods and to extended periods of cropping in many areas, with resulting increases in weed pressure.

Common challenges

Due to prevailing challenges such as low soil fertility and low soil moisture, it has been difficult to achieve the full potential of the existing production systems. Some of these challenges include:

Limited access to good quality seeds - Most rice farmers typically grow traditional varieties. In most cases, these varieties are well-adapted to local conditions and have low nutrient requirements, but produce low yields. In addition, farmers do not carefully select and handle the seeds to ensure purity and seed viability for the next season’s planting. They instead pick rice seeds from any remaining stock after harvest and preserve them for the next growing season. The seed problem has increased further in that there is no suitable national rice seed development programmes for the screening, testing and release of varieties to satisfy the demands of the specific ecologies, farmers, brokers and consumers.
Decreasing soil fertility - Most farmers grow rice as a monocrop, season after season, without any added inputs for soil improvement. Due to the continuous loss of nutrients with every harvest and leaching, soil fertility continues to decline. In the long run, nutrients become deficient thus affecting rice yields. Generally, nitrogen (N) and phosphorus (P) are the most limiting nutrients for rice production in SSA. For example, the humid forest agroecosystem of West Africa is characterized by highly weathered and strongly acid, low activity clay soils, Ultisols and Oxisols (with low P supply potential). About 70 % of the upland rice produced in the subregion is in this agroecosystem where N and P deficiencies are common.
Land shortage - Normally, land is left fallow to regenerate and restore the soil fertility through the decomposition of biomass. This fallow period has decreased considerably due to increasing population; the soil is not allowed to regain adequate fertility before it is used again for cropping. The continuous need for new virgin land has forced farmers to utilise marginal lands, for example wetlands, forest lands, and tidal lands for rice production. This has led to increased deforestation for upland rice and draining of wetlands for lowland rice production.
Soil erosion - Farmers grow rice along steep slopes of hills and mountains under upland rice cultivation. The removal of vegetation exposes the soil to the force of raindrops and destroys soil particles. The combined effects of raindrops and steep slopes promote the erosion of topsoil, leading to soil degradation.
Water problems - Water is the primary factor determining the success of rice crops. Most farmers rely on rainfall for rice cultivation. Cultivating land near rivers for rice often pollutes the rivers, especially in cases where pesticides and fertilizers are used in cultivation. Under rainfed lowland systems, the erratic nature of rain sometimes leads to either too much rainfall causing floods, or very little rain causing droughts; both of these conditions affect yields.
Weed problems - A major constraint to the production of rice under rainfed upland and lowland conditions are weeds, because of the favourable growing conditions. Weeds normally grow very fast and can outgrow the rice plants if the farmer does not intervene in time. They compete for space, nutrients and water, and also harbour diseases and pests. Furthermore, weeds also hamper harvesting activities and can ultimately reduce rice yields.
Pest and disease problems - Rice is generally not as vulnerable to insect pests during its growth compared to other crops. However, in areas where stemborers are present, this can pose some problems. Rodents and birds are the major problems for rainfed rice cultivation. Grass cutters/rodents can cause tremendous damage to the crop during its cultivation, especially after booting, while birds will destroy the grains especially during the grain-filling period. Quelea birds in great numbers can consume a substantial amount of rice grains on the field. But in situations where rice is grown continuously on the same fields without rotation, the risk of pests and diseases increases. Especially diseases like rice blast, rice yellow mottle virus and the bacterial blight are common in such areas.
High postharvest losses - Poor harvesting techniques, and untimely harvests cause the rice grains to shatter on the field before and during harvesting. Mixing seeds of different varieties also promotes high yield loss, as the varieties have different maturity periods and time for harvesting. Losses of up to 50 % have been reported in many rice growing areas, especially during drying and storage of harvested grains. Lack of simple and appropriate automation through farm machinery and equipment like harvesters and threshers also slows down the postharvest process and thus losses increase. Some of the problems can also be attributed to the weak rice extension system to help farmers learn about appropriate water harvesting and management technologies, improved production and postharvest management practises.
Low returns from rice production - Most rice farmers rely on rice production alone as the only source of income. This is risky, especially if the rice crop fails due to unpredictable weather conditions, disease outbreak or a drop in rice prices. Furthermore, due to the lack of labour-saving implements and machines for timely harvesting, the farmers cannot compete effectively with those using mechanization, who cultivate large tracts of land.

The objective of this guide is to introduce approaches to rice production which can be adapted to the prevailing local conditions to help enhance sustainable rice production and positive impacts on the environment. In the following sections, specific approaches necessary to address some of the above mentioned production challenges will be discussed.

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Rice: Background

Common challenges

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