EVALUACIÓN DEL PELIGRO DE LA INMERSIÓN DE CICLISTAS EN LA

HARCHAOUI,S.1_{, CHATZIMPIROS, P.}1

1 _{Laboratoire Interdisciplinaire des Energies de Demain (LIED), Université Paris Diderot, France.}

INTRODUCTION

Industrial nitrogen (N) fertilizers (Nind) have played a key role in global agricultural productivity and are

estimated to have underpinned a net doubling in global population over the 20th _{century (Smil, 2002;}

Erisman et al. 2008). N inputs to agriculture rely on two additional natural mechanisms, namely

atmospheric N deposition (Natm) and biological nitrogen fixation (BNF), but unlike Nind, the supply

capacity of those mechanisms is restricted by land availability. BNF is not performed by cash crop, but only by leguminous crops, mostly fodder crops, which compete for land with cash crops. In preindustrial systems, the necessity to set aside land for BNF was a major limiting factor of total

production. The use of Nind lifts this constraint, but increases the dependency of food production on

fossil fuels and induces emission of greenhouse gases. In addition, the resulting abundancy of Nind may

trigger poor N management practices and high N losses with severe consequences for ecosystems and

human health (Foley et al., 2011). The abundancy of Nind also drives the decoupling between vegetal

and animal farming systems, which hampers the recovery of manure N into crop production. The use

of Nind has deeply transformed the N operating space of agriculture by disconnecting total production

from N self-sufficiency. The implications of a sharp reduction of Nind (either due to climate policy, fossil

fuel use restrictions, societal demand for organic agriculture) on the feeding capacity of world agriculture have received little scrutiny (Erisman et al. 2008). This paper provides a modeling approach of the nitrogen operating space of agriculture and assesses scenarios of agricultural productivity and N self-sufficiency as a function of key structural agricultural variables.

MATERIAL AND METHODS

The study system is the utilized agricultural area considering N fixing land (sum of all N fixing

grasslands, fodder and food crops) and non-fixing land (major arable crops). Total N input (Ntot) to the

system is the sum of BNF, Nind and Natm, which is set constant to 5 kgN ha-1 yr-1. The N self-sufficiency

is defined as the ratio of BNF and Natm to Ntot. BNF is transferred from fixing to non-fixing land through

manure N recovery and cropland rotations. Manure N is calculated as a function of the nitrogen conversion efficiency (NCE) of feed to food by livestock. For ruminants, feed is provided by BNF land

and equals the above-ground N yield (BNFyield). Total BNF rate (rBNF) is the sum of BNFyield plus the non-

extracted N calculated from the N harvest index of fixing crops and assumed to be transferred to non- fixing land through crop rotations. The N net production is defined as the sum of the vegetal and livestock production of agriculture, minus the feed calculated from livestock NCE. The share of grain used as feed (α) is a key parameter. Table 1 summarizes the structural variables of the model and the values used in the simulations inspired by results from historical analysis for France (Harchaoui and Chatzimpiros, accepted) and by current world estimates. The simulations consider constant

fertilization rate on arable land for a crop yield of 110 kgN ha-1 _{obtained with nitrogen use efficiency}

(NUE) of 70 % which can both be considered as optimal in current agriculture. RESULTS AND DISCUSSION

Figure 1 quantifies the net N production of agriculture as a function of the N self-sufficiency for the three scenarios of table 1. The share of grain to livestock is set at 35 % in all scenarios, which is the current value for both France and the world (Harchaoui and Chatzimpiros, accepted; Foley et al., 2011). In contrast, the production from ruminants increases with BNF through a structural correlation which is possibly counterintuitive. It highlights the pivotal role of ruminants in N self-sufficient systems (organic agriculture) and challenges the visions that combine agricultural N self-sufficiency and

vegetarian diets. The results highlight the relevance of high manure recovery rates in particular in high N self-sufficiency regimes. Without N industrial fertilizers, the model predicts a drop by half of the global N net production which is in line with estimates from Smil (2002) updated by Erisman et al (2008). There is a variety of options to feed the 9.7 billion people projected by FAO in 2050. Under the S1 scenario, the N self-sufficiency would drop below 0.25. If the production was to be sustained solely

by BNF, major changes including a tripling of rBNF (from 12 to 35 kgN ha-1) and an increase of NUE to

70% would be necessary (S2 scenario). The very high scenario (S3) considers an increase by an order

of magnitude of current world average rBNF and may only be conceivable for a handful of western

countries. The trajectory of France in fig1 is driven by the concomitant increase of N yields and NUE.

Table1. Structural agricultural variables and values used in the simulations inspired by results from historical

analysis for France (Harchaoui and Chatzimpiros, accepted) and from current world estimates. Sources: (1)

Lassaletta et al. (2014) (2) Smil (2002), (3) FAOSTAT (2017),(4) Foley et al (2011), (5) Calculated.

France World Scenarios

Variables 1980- 1991 1992- 2002 2003- 2013 2013 Current

world High Very high rBNF (S1) rBNF (S2) rBNF (S3)

rBNF fixing kgN ha-1 35 38 35 12(2) 12 35 35 -> 100

Fixing to total area % 49 45 44 67(5) _{variable variable variable}

N industrial kgN ha-1 _{78 79 73 22}(3) _{variable variable variable}

Yield non-fixing kgN ha-1 _{97 110 119 60} (5) _{60 110 110}

Grain to livestock α % 39 38 37 35(4) _{35 35 35}

Livestock NCE % 21 21 20 - 22 22 22

NUE non-fixing (1) _{% 43 60 71 - 50}(2) _{70 70}

Net production kgN ha-1 _{38 46 51 13}(3)

% Livestock in net N prod. 25 20 18 15 N self-sufficiency % 25 19 20 34 (5)

Figure 1. Relationship between maximum N net production per ha and N self-sufficiency for three scenarios. i)

Current average world N fixing rate (rBNF = 12 kgN ha-1) ii) High rBNF= 35 kg ha-1 (western countries) iii) Increasing

rBNF (from 35 to 100 kgN ha-1) as a positive function of N self-sufficiency. In each scenario, the range of net N

production is determined by the manure recovery rate βϵ[0, 1]. The color code indicates the share of livestock in total net production. The trajectory for France (1980 to 2013) is indicated for comparison.

CONCLUSION

This paper models the N operating space of agriculture by connecting N self-sufficiency to net N production.

Foley, J. et al. 2011. Solutions for a cultivated planet. Nature 478(7369): 337–342

Harchaoui S., Chatzimpiros P., accepted. Energy, nitrogen and farm surplus transitions in agriculture from historical data modeling. France, 1882-2013.

Lassaletta, L. et al. 2014. 50 year trends in nitrogen use efficiency of world cropping systems: the relationship between yield and nitrogen input to cropland. Environmental Research Letters 9(10): 105011.

IMPACT OF NITROGEN MANAGEMENT PLANS ON WINTER SOFT WHEAT YIELD AND NITROGEN BALANCE AT