Benefits of nitrogen for food, fibre and industrial production

Abstract

Nature of the issue • Reactive nitrogen (N r ) has well-documented positive eff ects in agricultural and industrial production systems, human nutrition and food security. Limited N r supply was a key constraint to European food and industrial production, which has been overcome by Nr from the Haber–Bosch process. • Given the huge diversity in N r uses, it becomes a major challenge to summarize an overall inventory of Nr benefits. This full list of benefits needs to be quantified if society is to develop sound approaches to optimize Nr management, balancing the benefits against the environmental threats. Approaches • When reviewing trends in European N r production rates, including those from chemical and biological fixation processes, and the consumption of this Nr in human activities, agriculture is by far the largest sector driving Nr creation. • Particular attention has been given to relationships between N application rates, productivity and quality of products from major crops and livestock types, including consideration of the mechanisms underlying variations in N response/outputs and the derived impacts on land use and land requirements. Key findings/state of knowledge • The economic value of N benefits to the European economy is very substantial. Almost half of the global food can be produced because of Nr from the Haber–Bosch, and cereal yields in Europe without fertilizer would only amount to half to two-thirds of those with fertilizer application at economically optimal rates. • There is a wide variety in N responses at field level. For cereals, nitrogen productivity, also termed the agronomic efficiency, averages 41 kg grain per kg applied fertilizer N across the EU countries, with significant variation between the member states. Variation reflects differences in crop type, farm type, cropping practices, area, region, soil fertility and climate. • Farmers have an economic incentive to apply only the economically optimal rate of fertilizer N, but there is no strong incentive to increase N use efficiency as the economic return on using fertilizer N is very robust, especially in high value crops. However, recent initiatives to reduce environmental impacts of Nr losses have led to an increase of N use efficiency in both crop and livestock production. • Increasing fertilizer prices and climate change will create new incentives to increase N use effi ciency. Th ere are ample options to achieve this via N-conserving field practices such as catch crops, reduced soil tillage, better estimation of crop N requirements and improved timing and placement of N inputs. Also modifications to livestock diets, enhanced recycling of livestock wastes, prevention of ammonia loss from animal housing and fi eld manure application can enhance benefits per unit applied Nr . Plant materials with improved composition of major storage compounds and novel feed additives, e.g. proteins from bio-fuel production, can also improve feed N responses per unit mass Nr used. Recommendations • Legislative drivers to reduce Nr use, including mineral fertilizer, must take account of the nitrogen benefits in agricultural production needed to maintain food and energy security, given the limited options to increase arable land area. • New technological tools should be implemented to improve nitrogen-effi ciency and the overall benefits of Nr use.