Scientists tip on rice farming methods

Rice with its botanical name Oryza sativa is one of the most consumed cereal food crops in the world, in particular in sub-Saharan Africa.

However, competition from weeds is the most important yield reducing factor in African rice production systems.

Generally important weed management practices in rice are controlled flooding and the use of herbicides.
Smallholder rice farmers in Africa including Uganda however often lack the necessary water management infrastructure, access to affordable, good quality herbicide products and knowledge and equipment for their safe and effective application.

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Against this challenging backdrop, effective and affordable weed management strategies are highly needed.
As such scientists majoring in cereal crop research keep producing literature on weed ecology and management in African rice systems for rice farmers to be aware of the weed challenge.

In Uganda, scientists handling rice research to develop improved varieties are at the National Crops Resources Research Institute Namulonge.

Rice varieties for farmer adoption
Farmers in Uganda have been growing mainly lowland rice of land race type such as K8, K98, K-5, super and Sindano but in 2002, scientists at NaCRRI developed Nerica rice varieties namely Nerica 1- 10 with Nerica 4 variety adopted most because it is high yielding.

The scientists have developed other varieties namely Namche3, 4, 5, Nerica6, 10 and Nerica5 among others. For the regions characterised by lowland, the scientists have developed NamChe3, 4 and Namche5 varieties. 
All these rice varieties apart from facing the challenge of pests and diseases, are faced with weed challenge which reduces the yield drastically.

It is for this reason that the director of NaCRRI Dr Geoffrey Asea and Dr Kazuhiko Yagi the chief advisor for Promotion of Rice Development Project with a team of other scientists produced a book titled Major Rice Weeds in Uganda.

The book highest the major types of Rice weeds farmers in Uganda are faced with and management practices. Seeds of Gold obtained the book and perused through with details below.

Weed control 
To a greater extent than in the management of insect pests and diseases, the management of weeds requires integrated strategies to be successful.

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While in some production systems, herbicides may provide the main means of control, these alone are unlikely to be successful unless combined with good land preparation and, in the lowland systems, good water control.

No one weed control method is likely to control all weeds and in the long term this can lead to a build-up of certain species.

The combination of direct weed control methods, such as herbicides or hand weeding with indirect methods such as land preparation, flooding and a competitive crop, will help prevent this situation.

A combination of direct weed control methods such as herbicide use with subsequent hand weeding can result in improved yields.

The optimum combination of weed control methods will depend on the farming system, economic conditions and farmers’ resource and knowledge base.

Land preparation
Tillage serves to provide a suitable soil tilth for a seedbed and control weeds prior to crop establishment. In smallholder systems, practice varies from zero tillage, as in many of the systems of shifting cultivation, to repeated deep cultivation to remove troublesome perennial weeds, such as Oryza longistaminata which has an extensive rhizome system.

Shallow tillage is often ineffective in controlling weeds and regardless of tillage practice, post-emergence weed control is normally necessary.

Flooding
The flooding of fields is the most effective method of cultural control of weeds in rice. Flooding to a depth of 10cm prevents germination of most weed seeds and kills the majority of weed seedlings. Normally, flooding is used in conjunction with other control measures, such as herbicides or hand weeding.

However, for flooding to be successful, water levels must be maintained and fields well levelled to ensure an even depth of water.

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In many smallholder schemes, limited irrigation water and poor land development can be major constraints to effective weed control.

Hand weeding
Hand weeding is the most widely used weed control method, with availability of labour being the main limitation to its effectiveness.

In some areas, adoption of line planting in transplanted rice has allowed the introduction of rotary weeders for cultivation between rice rows, considerably reducing labour requirements for weed control.

Fallow systems
Man’s inability to control weeds is one of the major constraints to continuous cultivation in the tropics and is a particularly acute constraint for those with limited resources and little access to appropriate technologies.

After initial clearance of the farmland, weed growth consists largely of broadleaf weeds and forest regrowth, though with repeated cropping, more problematic grasses invade the fields.

Studies have shown that weed growth following a fallow of less than three years was almost twice that following a fallow of five or more years. Where the cropping cycle is short compared to the length of fallow, farms rapidly regenerates from seeds, roots and cut stumps.

However, repeated cultivation allows invasion by annual and perennial weed species and replacement of native forest species by weeds such as Imperata cylindrica and Chromolaena odorata.
While shifting cultivation has been criticized as being wasteful of land and forest resources, it is still the main means of production for many resource-poor farmers.

Crop competition
Rice is not very competitive with weeds during the seedling stages, though this can be an important factor during the vegetative and reproductive stages.

Crop competitiveness with weeds is particularly important to limit weed infestation after the initial weed control treatments, such as land preparation, herbicides and hand weeding, have been undertaken.
Crop and weed interactions largely involve the competition for light, water and nutrients.

Chemical control
The importance of herbicide use in the tropics including Uganda is closely related to the cost and availability of labour.