How to measure GAI accurately and manage your rape more easily‏
With the widely variable sizes of oilseed rape crops this season, rape growers will need to assess each crop individually for growth regulation and nitrogen in order to optimise canopy and maximise yields. Developed by BASF and ADAS, the web-based Canopy GAI tool, which can be found on www.totaloilseedcare.co.uk web site, will make this assessment much easier and much more accurate.
"Canopy management in oilseed rape in the spring aims to create an optimum sized canopy that is able to maximise the crop's yield potential. It involves tailoring early spring inputs to the state of the crop, its canopy size, its plant population as well as seasonal and environmental factors. But you need to be able to accurately assess when and where inputs are required. This is quite a challenge this spring as there are crops which are particularly small and crops which are particularly large and they will need different management strategies," says Diane Heath, BASF Oilseed Rape Product Manager.
"This is where using the Green Area Index (GAI) comes in. The GAI is the ratio of green tissue area to ground area and it is a way of measuring canopy size. Economic benefits from plant growth regulators have been observed in crops that have a GAI greater than 1.0 in March or crops with a GAI greater than 2.0 in April," she says.
"In the past, growers assessed GAI visually or used reference photographs. Last year a new computer-based tool allowed growers to upload photographs of their own oilseed rape crops and get instant assessment of Green Area Index (GAI) for individual fields relayed back to them."
"This tool is a really important and practical advancement in managing canopies effectively and makes life a lot easier. All farmers and advisors have to do is to go on-line at www.totaloilseedcare.co.uk any time, click the Canopy GAI tool button and follow the instructions. It is simple to upload photographs and, once loaded onto the site, an accurate assessment of GAI is relayed on the screen within a few seconds. To gain the most accurate results, digital photographs in a JPEG (jpeg) format should be taken directly above the crop and cover an area of approximately 1 metre by 1 metre. It is advisable to avoid taking photographs when it is sunny, as this causes too many shadows," explains Ms. Heath.
Dr. Peter Berry of ADAS High Mowthorpe agrees that the GAI tool will be very important this year as crops are so variable. "We are seeing massive variation in growth stages of winter oilseed rape. Some crops drilled in September in dry conditions established poorly and have grown little through the winter and consequently are small and under developed. These crops need alot of looking after and may well benefit from an early Nitrogen spilt. Other crops are much more vigorous following good establishment and growth and are well-developed with large plants. These will need completely different management, probably delaying nitrogen and the use of an effective growth regulator such as Caramba. It is particularly important this year that crops are individually assessed and individually managed. Whether you have small or large crops, or indeed both on the farm, it is possible to manage them effectively in order to get the best canopy structure and so optimum yields."
