IFS WEBINAR – Aspects of N use efficiency management Wednesday 30 October 2024 13.00 GMT

Should we grow nitrogen on trees? Potential to improve nitrogen use efficiency by use of perennial mobile green manures

Clo Ward, Ecodyfi, UK

Supplying nitrogen (N) to soil, whether by mineral fertilisers or by organic techniques such as N-fixing green manures presents environmental challenges. Green manures provide organic matter which improves soil functioning and can result in carbon sequestration, but the practice requires cropland to be periodically taken out of production. Crop-available nitrogen can be lost from soil by leaching of nitrates or emission of nitrogen gases including the powerful greenhouse gas nitrous oxide. Precision agriculture allows nitrogen fertiliser applications to be targeted to meet crop demand, thus increasing efficiency and reducing nitrogen loss. Such targeting is difficult, however, when adding green manures which are usually incorporated into soil by tillage.
An alternative to green manures grown in rotation is the use of ‘mobile’ or ‘cut-and-carry’ green manures which are harvested from a separate area and added to cropland, so allowing more flexibility in timing amendments to meet the crop’s nutrient requirements. Mobile green manures are usually non-woody species such as clovers or vetches, but for additional environmental benefit, we propose including N-fixing and N-accumulating trees and shrubs, to produce foliage to be used as fertiliser. To test the feasibility of this technique we conducted pot and field experiments monitoring crop N uptake, biomass production and soil mineral N from fertilisation by foliage of Alnus glutinosa (alder), Gunnera tinctoria (gunnera), and Ulex europaeus (gorse), compared to the conventional green manure Trifolium pratense (red clover) and ammonium nitrate fertiliser.
Subsequently, the Perennial Green Manures project has facilitated trials by horticultural growers fertilising crops with various materials including dried and pelleted tree leaves. It is envisaged that organic fertiliser could be produced in mixed-species ‘fertiliser forests’ which could help address the environmental need for increased tree cover, while also contributing to food security. The webinar will discuss the results of the experiments and the opportunities for development of the technique.
Ward, C. R., Chadwick, D. R., & Hill, P. W. (2023). Potential to improve nitrogen use efficiency (NUE) by use of perennial mobile green manures. Nutrient Cycling in Agroecosystems, 125(1), 43-62.

Effects of manure and mineral fertiliser nitrogen supply on crop nitrogen utilisation and nitrate leaching on cut grassland

Wim van Dijk, Wageningen University and Research, The Netherlands

In the Netherlands, the use of animal manure nitrogen (N) instead of mineral fertiliser N on grassland and its implications for nitrate leaching are a frequent topic of debate. To test the impact of fertilisation type on N utilisation by grass and nitrate leaching, a multi-year field experiment and a greenhouse experiment were carried out.

In the field experiment, various types of mineral fertiliser (calcium ammonium nitrate, urea with urease inhibitor) and manures (cattle and pig slurry, digested cattle slurry) were compared at an annual rate of 300 kg N per ha. for one, two and three consecutive years. This setup was used to determine both the N utilisation (apparent N recovery) in the year of application, as well as the legacy effect of prior fertilisation. In addition the residual soil mineral N in the autumn in the 0-60 cm layer, and the nitrate concentration in the upper groundwater were measured annually.

In addition to the field experiment, a pot experiment with grass was conducted in which mineral fertilisers and cattle manure products were compared. Besides crop N uptake, nitrous oxide emissions and nitrate leaching were measured. At the end of the pot experiment, potential denitrification rate was measured in the top soil.

In the webinar the results will be presented and discussed.

Co-authors: Rietra, R.P.J.J. and Ros, M.B.H.

 

BASIS FACTS CPD points will be applied for.

 

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