The area of carrots stored under straw is estimated at around 3,000-4,000ha per annum. Current estimates for the costs of straw-based field storage systems are around £4,000-£5,000 per hectare on top of crop production and harvesting costs. However, vulnerability of straw supply and problems with black-grass are becoming increasingly important. Consequently, carrot growers urgently need to examine and evaluate alternative options to current in situ field storage practice.
Making more efficient use of straw by keeping it dry would have a major impact on the amount of straw required. This could be achieved by covering the top of the straw layer with a layer of polythene.
Results to date of HDC project FV 398a indicate that a 5cm layer of straw covered with polythene would provide the equivalent insulation to 28cm of uncovered wet straw, or 20cm of uncovered dry straw. It should be noted that these are theoretical calculations, so it is vital that they are tested experimentally before wide-scale adoption.
Theoretical calculations of the insulation values achievable indicate that a reduction in straw usage of up to 67 per cent could be achievable by moving to a poly-over-straw system.
This could amount to a saving of some £2,000 per hectare, which would be equivalent to at least £6m per annum for the industry as a whole.