* Potato crop hit by moves against al Qaeda
* Authorities restricting fertiliser used in bombs
* Potato prices soar in local markets
AIN DEFLA, Algeria, April 20 (Reuters) - Algeria is suffering a potato shortage because officials have imposed strict controls on the use of fertiliser to stop al Qaeda militants using it as a bomb-making ingredient, farmers said.
Security experts say ammonia, used by farmers to improve crop yields, has also been found in bombs detonated by Algerian militants affiliated to al Qaeda.
State security forces in this North African country have cracked down hard on the insurgents but farmers say there has been an unforeseen consequence: a kilo of potatoes in the capital now costs more than three times what it used to.
"Lack of fertilizers, particularly ammonia, is the key reason behind the rise in the price of potatoes," Azizou Redouane, a 28-year-old farmer from the Ain Defla region, 120 km (75 miles) west of Algiers, told Reuters.
"Ammonia ... guarantees a good harvest," a sweating Redouane said as he stood in his 30-hectare potato field.
"To prevent armed groups from fabricating bombs with ammonia, the security forces are tightening control over the distribution of fertilizers.
"When you ask for 10 kg of ammonia you get only 5 kg and you need to wait a long time before the local chamber of agriculture deals with your request," he said. "The direct impact is a poor harvest and a rise in prices.
Algerian farmers have to apply to their local chamber of agriculture, a farmers' syndicate, for approval to obtain fertiliser.
Farmers said even if they were given clearance to buy ammonia, in some cases they were still required to bring the chemical to their farms under police escort to make sure it did not fall into the wrong hands.
"They tell us fertilizers are used by terrorists to fabricate bombs. This is why it is very difficult to get some ammonia to feed the land," said another farmer, Belkacem Aisssa.
"Without fertilizers it is impossible to have a good yield," said Aissa, who was working his 18-hectare field. "I used to get 350 quintals (35 tonnes) per hectare when I used enough fertilizers, and now I have 250 quintals per hectare."
The impact of the lower potato yields is clear in the vegetable markets of the capital, Algiers. In the past week, the price for a kilo of potatoes reached a record 100 dinars ($1.37), compared to a normal price of under 40 dinars.
Consumers are feeling the effect.
"Too expensive, it is too expensive. I am angry and I don't know how to feed my six kids," 71-year-old Zakia Rabehi told Reuters in one of the city's markets.
Food prices are already a sensitive issue in Algeria, a country of 34 million people which has to bring in much of its wheat and other foodstuffs from abroad at considerable expense. Bread and milk are subsidised by the government.
Algeria was plunged into a civil conflict between government forces and Islamist rebels in 1992 after the military scrapped legislative elections a radical Islamic party was poised to win.
International non-governmental organisations estimate that 200,000 people died in the subsequent violence.
The violence has fallen sharply in the past few years but a hard core of militants associated with al Qaeda continues to launch sporadic strikes against government targets. (Editing by Giles Elgood)
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