Agriculture and Agricultural Systems

Crop ecology deals with agricultural ecosystems that are manipulated by man to funnel the maximum energy into usable products (food and raw materials). Agricultural ecosystems show generally lower biodiversity and autonomy and a shorter trophic chain than natural ecosystems. The main features of farming systems are productivity, stability, resilience, and sustainability, the latter indicating the ability to maintain a certain level of production indefinitely. Production of agricultural systems requires inputs of matter, energy, and information. Normally the economic optimum provision of inputs is below that necessary to achieve maximum production. Various parameters have been defined to characterize the productivity of agricultural systems (potential, attainable, and actual yield). Agricultural systems may be classified according to different criteria. According to the length of the trophic chainTrophic chains, the higher efficiency is obtained with a system where crops are directly used by humans. However, animal husbandry allows the exploitation of areas marginal for food crop production and the use of residues. According to intensification, agricultural systems have evolved from subsistence agricultureSubsistence agriculture to intensive modern systems where the main challenge is sustainabilitySustainability. The carrying capacityCarrying capacity, the number of animals that can be fed by the primary productionPrimary production of a given area, may be also calculated for humans growing cereals taking into account that an individual requires around 300 kg grain/year to meet the energy and proteinProteins demand.