Variable renewable energy penetration impact on productivity: A case study of poultry farming.

Like all current industrial systems, agriculture overwhelmingly relies on energy supply from controllable sources, mainly fossil fuels and grid electricity. Power supply from these sources can be adapted to perfectly match the timing of power requirements of demand systems. The energy transition largely consists in substituting renewable power-which is intermittent by nature-to controllable sources, leading to disconnection between instantaneous power production and demand. Energy storage is a potential solution for balancing production and demand and safeguarding the operating conditions of the demand system. In this paper we quantify the effects of renewable power supply (solar and wind) on the operation of a standard poultry farm. We model the balance of power generation and demand considering the growth conditions of poultry and local weather data including temperatures, wind speed and solar radiation. We assess scenarios of renewable power supply in function of the size of the power plant, the wind-to-solar power generation mix and energy storage, and assess the impact of power supply patterns on the operating intensity (productivity) of the demand system. We show that, with a limited storage capacity, it is possible to achieve non-negligible shares of renewable power penetration without major loss in farm productivity. However, a full transition to renewable power would require the combination of i)-large energy storage compared to the annual demand, ii)- significant oversizing of the power production plant, and iii)-the exclusion of power generation combinations (wind/solar) that deviate from the timing of demand. Storage and power plant oversizing is all the more critical as production and demand are uncorrelated over the year. The ratio of useful to unused energy storage by the end of the year varies with the energy mix and operating intensity (productivity) of the farm. We discuss the implications of different energy configurations on the performance of the demand system.

Sevenfold variation in global feeding capacity depends on diets, land use and nitrogen management.

Harvested food carries a fraction of the nitrogen applied through fertilization; the remainder is typically lost into the environment, impairing planetary sustainability. Using a global agriculture model that integrates key drivers of food production and nitrogen cycling, we simulated upper bounds to global feeding capacity-and associated nitrogen pollution-as a function of nitrogen limitation under organic and industrial fertilization regimes. We found that the current agricultural area could feed ~8-20 billion people under unconstrained industrial fertilization and ca. 3-14 billion under organic fertilization. These ranges are inversely correlated with animal proteins in human diets, and are a function of feed-food competition, grassland-to-cropland allocation and-in the case of organic fertilization-nitrogen use efficiency. Improved nitrogen use efficiency is required to bring nitrogen pollution within planetary sustainability limits and is also essential in narrowing down food productivity gaps between organic and industrial fertilization regimes.

Time dynamics and invariant subnetwork structures in the world cereals trade network.

The development of industrial agriculture has enabled a sharp increase in food trade at the global scale. Worldwide trade underpins food security by distributing food surpluses to food deficient countries. The study of agricultural product flows can provide insights on the complex interactions between exporting and importing countries and the resulting network structures. Commercial partnerships between countries can be modelled using a complex network approach. Based on the detailed trade matrices from FAO covering the period from 1986 to 2013, we present an analysis of the world cereal trade in terms of weighted and directed networks. The network nodes are the countries and the links are the trades of agricultural products in mass. We reveal the changing topology and degree distribution of the world network during the studied period. We distinguish three entangled subnetwork structures when considering the temporal stability of the trades. The three subnetworks display distinct properties and a differential contribution in total trade. Trades of uninterrupted activity over the 28-year study period compose the backbone network which accounts for two thirds of all traded mass and is scale-free. Inversely, two thirds of the trades only have one or two consecutive years of activity and define the transient subnetwork which displays random growth and accounts for very little traded mass. The trades of intermediate duration display an exponential growth both in numbers and in traded mass and define the intermediate subnetwork. The topology of each subnetwork is a time invariant. The identification of invariant structures is a useful basis for developing prospective agri-food network modelling to assess their resilience to perturbations and shocks.

Nitrogen, land and water inputs in changing cattle farming systems. A historical comparison for France, 19th-21st centuries.

This paper provides an original account of the long-term regional metabolism in relation to the cattle rearing in western France starting by the precise formulation of animal diets at three key dates of the 19th, 20th and 21st centuries. We established links between the demand in fodder of the meat and dairy sectors and the necessary inputs of nitrogen, water and land as well as the land cover changes occurring on the affected local and remote cattle acreage. The average agricultural productivity for fodder supply is estimated at about 50 kg N/ha in the mid-19th, 54 kg N/ha in the early 20th and 150 kg N/ha at the turning of the 21st century. Jointly for the dairy and meat productions, the potential efficiency in the conversion of the vegetal into animal protein more than doubled over the studied period, passing from less than 9% in the 19th to 20% in the 21st century. The current cattle sector is sustained for about 25% by land situated beyond the regional frontiers and uses water at intensities that approach or exceed the availability of renewable water. The nitrogen pollution is expressed in terms of the Net Anthropogenic Nitrogen Inputs (NANI) and, by comparison to the N recovered in products, is used to define the N-Environmental Efficiency of the farming. We discuss the historical succession of the factors that contributed to the growth of the meat and milk production and make a comparison of the impacts and policy between the local and distant resources.