Nutrient Budgeting at James Hutton Institute

CENTRE FOR SUSTAINABLE CROPPING

BY ANDREW CHRISTIE FIELD AGRONOMIST

The Centre for Sustainable Cropping at the James Hutton Institute’s Balruddery farm was set up in 2009 as a platform for evaluating the long-term impacts of an integrated cropping system on whole-system sustainability.

The Integrated system, which applies direct drill, cover cropping, precision farming, reduced and targeted input techniques, is compared to a conventional, plough based, highly intensive system on six crops in rotation, covering the most widely grown arable crops in the UK (potatoes, winter wheat, winter barley, winter oilseed rape, field beans and spring barley).

From an agronomist’s perspective, the platform, which is the first of its scale in the UK, offers an opportunity to test new developments on the Integrated, direct drilling system and apply ideas already proven in other territories to a North-East Scotland context. This provides an opportunity to extend no-till systems from the dryland areas where these techniques were pioneered to new regions posing a completely different set of challenges and requiring novel solutions.

Nutrient Use Efficiency forms an integral part of the overall integrated management system which iteratively applies and tests new techniques to improve environmental and economic sustainability and transition towards a system which would now be classed under the umbrella term of regenerative agriculture. Techniques being applied are as follows:

Routine sampling for Phosphate and Potash allows us to apply a nutrient budgeting technique with the aim of maintaining status at level M- (or 2- in England & Wales), where soils are in balance between starvation and over-supply. Where this is achieved, conditions are optimal for plant uptake avoiding ‘locking up’ nutrients and reducing the potential for leaching. Using this technique there is potential for applications of Phosphate to be reduced by up to one third, Potash halved, and where organic manures are applied, mineral fertiliser use may be completely omitted in some cases.

ACCOUNTING FOR SOIL NITROGEN SUPPLY

Nitrogen, being an element which is easily leached, can cause problems of eutrophication and high nitrate levels in groundwater. A nutrient budgeting approach uses a measure of Soil Nitrogen Supply (SNS) in calculating crop requirements, which allows a reduction in overall fertiliser inputs. Conventional estimates of crop requirement do not accurately account for SNS and therefore where this ‘extra’ soil nitrogen is surplus to requirement and potentially leachable. Even where SNS is at low levels, there is a greater benefit in protection from diffuse pollution in the overall water catchment area. For example, where a low SNS value of 5kgN/ha is estimated to become crop available, this may only reduce application rate by 14.5kg/ha of 34.5%N fertiliser for a given field. However, if this practice is applied to a water catchment area, say for example, 5000ha, this would multiply up to an environmentally (and economically) significant input of 72.5 tonnes of 34.5%N fertiliser which need not be applied.

VARIABLE RATE APPLICATION

Targeted applications of Nitrogen using Green Area Index NDVI (Normalised Difference Vegetation Index) maps to create Variable Rate Application Maps are a useful tool for boosting productivity without increasing overall fertiliser use, particularly in winter cereals. Areas of the field are split into levels based on ground cover and fertiliser rates are adjusted to each level. In early season, where establishment and tiller survival are key, applications are weighted for higher rates on the lesser areas to produce a more uniform canopy. For later applications, at stem extension, the aim is to boost yield potential in the more productive areas. Monitoring is important as some ground truthing is required before application and productive areas are best identified using yield data and soil mapping.

NDVI Map gives vegetation index Vegetation Zones used to create application map

Variable Rate Application Map exported to spreader

Liebig's Law states that yield is limited not by total resource availability but the scarcest nutrient present. So, where there are deficiencies of micronutrients, further application of base macronutrient fertilisers may mask symptoms without translating into yield improvements. At the Centre for Sustainable Cropping, we aim to maintain yields by providing for the full suite of elemental requirements. Where soil levels are low and deficiency symptoms are likely, crop protection plans include targeted trace elements at key timings. At timings where transient deficiency symptoms are expected, e.g. drought conditions during peak growth, targeted applications of foliar fertilisers and biostimulants are used to relieve stress and improve plant fitness. There are two main benefits of this approach: crop yield potential is protected by providing the required nutrients at the right time for the plant, and secondly, plant fitness is improved through induced disease resistance triggered by elicitors in biostimulants together with some biocidal activity of certain micronutrients, offering improved resilience to disease infection.

SOIL pH AMENDMENTS

Last but certainly not least, it is important that soil pH levels are correct for the crop being grown for any management system to work effectively. Regular applications of pH neutral or slightly alkaline organic manures within an Integrated system may act as a buffer for acidification, thus maintaining optimal conditions. In very acidic soils, where uptake of all nutrients are restricted, the ageold agricultural good practice of rotational liming remains the single most effective management technique which can be applied for sustainable production and resource use efficiency.