Keywords: Nitrogen, phosphorus, fertiliser, efficiency, innovation, sustainability.
Crop nutrition and its current enabling fertiliser technologies are at a crossroads; on the one hand they can justifiably claim to have played a pivotal role in the past green revolution, but on the other, their offer to enable further intensification of developed agricultural systems appears unsustainable. Fertilisers have all but eliminated nutrient deficiencies in temperate crops, and thereby they have at least doubled food production. Yet current crop nutritional philosophies, as considered here for nitrogen (N) and phosphorus (P), regard fertiliser use as inherently coupled to crop productivity. Given that current fertiliser technologies are inefficient, with substantial environmental costs, a ramping up of fertiliser use to support crop yield enhancement appears unsustainable.
This paper examines how inefficiencies arise when applying N and P and successively transferring them through food and fuel supply systems, so that it can highlight points at which innovation should most effectively decouple fertiliser use from crop productivity.
~ Fertiliser recommendations remain imprecise. The best means of improvement will be to facilitate perception and validation of nutrient status within individual fields, but big gains in precision will prove difficult because weather, and its interactions with cropping systems, is likely to remain unpredictable.
~ Crop recovery of fertiliser N averages at only ~60%, and recovery of fertiliser P is much worse. Unrecovered N is immobilised by soil biomass before it can be acquired by the crop and most unrecovered P is ‘lost’ through long-term soil fixation. Undoubtedly fertilisers increase soil fertility, but fertility of tilled soils is bad for nutrient pollution. Concerted genetic, chemical and engineering innovations must be found, to avoid soil immobilisation of N and P as far as possible.
~ Crop demands for N and P include substantial storage in shoots and seeds which, it is argued, are unnecessary in crops which are closely managed, and unnecessary for most end-uses, including seedling regeneration. Breeders of some species have achieved reduced nutrient intensities of crop products, and mutants with reduced nutrient storage offer scope to abate crop nutrient demands further.
~ Weak specifications by end-users, particularly livestock feeders, for N and P contents of crop products provide growers and breeders with inadequate signals for innovation. Whilst processors may passively accommodate crop products with reduced nutrient intensities, consumer pressure for green credentials should increasingly energise crop processors to seek means of employing only essential crop nutrient contents.
These large emerging opportunities for nutritional innovation, along with food security concerns, bring concomitantly large and urgent challenges. Clearly investors taking up the new challenges must integrate the relevant sciences and technologies to enable most effective progress. The International Fertiliser Society could assume a new role here, extending its remit from fertilisers themselves to the full breadth of nutritional systems in agriculture, providing effective leadership towards developing sustainable nutrient supply chains, delivering food and energy with only their essential nutrient intensities, and with minimum waste.
Roger Sylvester-Bradley, ADAS Boxworth, Cambridge CB23 4NN, UK. (Corresponding author)
Paul J A Withers, School of Environment, Natural Resources and Geography, Bangor University, Gwynedd LL57 2UW, UK.
27 pages, 8 figures, 4 tables, 64 references.