"Are you used to going for a number one in the back of your garden?" asks French design studio Faltazi. "Do not waste this valuable golden fluid by sprinkling on inappropriate surfaces!"

Their solution to the problem of peeing al fresco is l'Uritonnoir, a hybrid of a urinal ("urinoir" in French) and a funnel ("entonnoir") that plugs into a straw bale to make your very own urine upcycling factory.

As the bale is filled with your "liquid gold", the nitrogen in the urine reacts with the carbon in the straw to begin the process of decomposition - forming a rich mound of composted humus within 6-12 months.

L'Uritonnoir was originally dreamt up with summer festivals in mind, where straw bales are often in frequent supply, but portaloos are not. The device comes as a flat polypropylene sheet, which is folded into shape and slotted together, then threaded on a looping band around the bale, its funnel wedged deep into the centre of the straw to channel the fluid to the composting core. A deluxe version is also available in stainless steel - presumably for the VIP bale urinal area.

No more queue for the portaloo … l’Uritonnoir in action at a festival

The designers say their mission is to raise festival-goers' awareness of "dry urination, water saving and urine upcycling," and suggest the compost can kept on site and used in planters the following year to demonstrate its value. Production is set to begin in June, when the design will debut at the French heavy metal festival Hellfest.

L'Uritonnoir is just one part of Faltazi's wider Ekovores project, which is looking at how to introduce locally integrated systems of waste management and food production - from prefab modules for processing and preserving food, to facilities for reclaiming organic waste and an online platform for exchanging know-how.

Closed loop … beer to urine to compost and back

L'Uritonnoir joins a growing trend for dry, organic toilets, and it is not the first time that urinating on to straw bales has been advocated. In 2009 the National Trust introduced "pee bales" in some of its gardens for male members of staff to relieve themselves, and encouraged people to do the same at home.

"Most people can compost in some way in their own gardens," said Rosemary Hooper, Wimpole estate's in-house master composter. "Peeing on a compost heap activates the composting process helps to produce a ready supply of lovely organic matter to add back to the garden. It's totally safe, and a bit of fun too."