In the latest in his series on exotic and unusual harvesters, Nick Wigdahl looks at how rice is harvested.

Rice is the world’s third largest crop after maize, sugar cane and wheat. However, unlike the other two, it isn’t used for biofuel and so is the most important solely-food source.

A fifth of the world’s population relies on it as their basic food and 87% of the crop is grown in Asia. It is mainly an annual plant, except in some tropical areas where it is a grown as a perennial.

See also: Exotic and unusual harvesters – sugar cane

Not surprisingly, given its fundamental importance, a huge amount of research has gone into ways of increasing output, led by the International Rice Research Institute in the Philippines. There are many varieties of rice – Thailand alone has 3,500 of them.        

China is the biggest producer of rice, with 204m tonnes harvested in 2012. Not far behind is India with 153m tonnes, Indonesia with 69m tonnes, Vietnam with 44m tonnes and Thailand with 38m tonnes.

Not just an Eastern crop

European and US farmers also produce significant quantities of rice. Spain, Italy and Turkey are big rice producers. In the US, the Arkansas and Mississippi deltas are home to large-scale rice growing.

Average yields in 2010 averaged 4.3t/ha, but Australia manages to produce up to 10t/ha. Current EU prices are around €300/t (£210/t) for Japonica varieties and €270/t (£190/t) for Indica varieties, which looks rather more profitable than growing wheat.

Rice growing is a labour-intensive business and requires ample water. The traditional method is to flood fields, which keeps weeds and vermin down.

Flooding, however, is not mandatory and rice can be grown in big fields. However, this requires irrigation and effective weed control.

Rice’s ability to grow in very different conditions – from mountainside paddy fields to large fields in river deltas –  explains why harvesting equipment ranges from specially built harvesters through to large standard combines fitted with a rice header.

Companion planting – which is attracting more interest in the UK for other crops – is well understood by rice farmers. They often plant Azolla [mosquito fern], which fixes nitrogen and blocks out competing weeds.

Specialist harvesters

Metal cage-wheels may have gone out of fashion in the UK in the 1950s, but they are still popular in Spain in such areas as the Riumar Delta, where they are fitted to tractors for cultivating and spraying.

Most rice, however, is grown by small-scale farmers in paddy fields for which large combines are unsuited. There are 20 or more manufacturers of these rice harvesters, many of them small, hand-controlled machines with a cutting width of 1m, an engine of 15hp and an output of less than 0.2ha/hour.

Who produces the serious harvesting kit? It is mainly Kubota, Iseki and Yanmar, who have specifically designed rice combines. They have set up factories around Asia, with Kubota entering the Chinese market back in 1997.

Harvestking shows its prowess

The Kubota Harvestking is a good example of the type of kit used. It’s a relatively simple machine aimed at markets such as India. Rubber tracks cope with the boggy conditions and the grain tank holds a modest 750kg.

The engine develops 69hp and the tracks are 500×1,800 mm units. Travel speed is 6.3kph and harvesting speed 4.5kph. An axial flow-type does the main separation and output is a steady 2-4ha/day. Rice combines typically harvest at 25% moisture.  

The scale of these machines may be dwarfed by a big Claas, New Holland or Case scything its way through an East Anglian wheat field, but many of the technical features on a combine harvester are also present on this rice harvester.

Given their engineering prowess and recent purchase of Kverneland, it would not be that surprising if the company further moves into this market.

Conventional combines for rice

In the US, Australia and Europe, conventional combines on tracks are used to harvest rice. These used to be fitted with steel tracks, but there is a move to conventional rubber ones where conditions allow. 

Rice grains are delicate, so conventional rasp bars are replaced by spiked tooth ones.