Collecting information throughout the crop's lifecycle can help to improve the contribution of digestate to nutrition.
With the area of land being used to produce energy crops for anaerobic digestors (AD) increasing, so too is the use of digestate as an alternative source of fertiliser in arable rotations.
While these digestates offer a useful alternative to synthetic fertilisers, they must be used correctly in order to realise their full potential. That's according to ProCam agronomist Mark Burgess, who outlines five key considerations to ensure crops fed with digestate receive all the necessary nutrients.
"The nutrient content of digestates can vary considerably depending on the raw material that went into the AD plant and how efficiently it was converted into usable energy," Mr Burgess explains. "The following points should therefore be considered to ensure digestate provides adequate nutrition to commercial arable crops."
1) Accurate soil sampling
"Knowing where nutrients are needed is the first step for any effective fertiliser plan," Mr Burgess says. "As with synthetic fertilisers, regular soil sampling should be carried out to understand where and at what rate the digestate should be applied."
Mr Burgess recommends that all fields should be sampled at least every three years, with those earmarked for digestate application tested at least a few weeks prior to the ensuing crop being drilled. "For autumn sown crops that means soil sampling as soon as the combine has been through, or for spring crops as the winter draws to a close. This will allow enough time for any corrective nutrient applications to be made prior to the new crop being planted."
2) Be prepared
"Having access to the correct spreading equipment and being ready to use it at the optimum timing is key to getting the most from any source of nutrients," Mr Burgess says. "Workloads should also be prioritised to ensure crop development isn't delayed. For example, solid digestate material should be applied ahead of synthetic fertilisers to reduce the potential for the former to damage crops which have already emerged."
3) Know your digestate
Understanding the nutrient value of the digestate to be applied is key for two reasons, Mr Burgess explains: "Firstly, to ensure the crop receives all the necessary micro and macro nutrients and secondly, to ensure applications are made in accordance with any applicable regulatory standards such as those which dictate when and how much material can be applied in Nitrate Vulnerable Zones."
Regular sampling will also highlight whether any nutritional imbalances in the digestate will need to be addressed through the use of complementary fertilisers.
4) Leaf sampling
"As with any form of plant nutrition, one of the most effective ways to assess the
efficiency of digestate applications is to carry out in-season leaf sampling."
For combinable crops, Mr Burgess recommends leaf sampling should be carried out prior to the application of fungicides, with any nutrient deficiencies subsequently corrected through the application of an alternative fertiliser, soil conditioner or foliar feed.
"It is particularly important to monitor magnesium levels, especially in crops grown on chalk, as the high levels of potassium often present in digestate can create issues with its uptake."
5) Monitor grain quality
In addition to pre-season soil sampling and in-season leaf analysis, Mr Burgess also advocates the use of post-harvest grain testing to highlight any short-falls in nutrition. "Grain analysis can provide a clear indication of whether or not the crop received the nutrition it needed throughout the season and, if something was amiss, allows lessons to be learned ahead of the next cropping cycle.
"The more information that is collected throughout the crop's lifecycle, the easier it is to make informed, proactive decisions to ensure the crop's needs are being met. And it is certainly cheaper in the long run to spend a little extra time and resource to carry out these tests than it is to lose yield as a result of inadequate nutrition."
