TASC Agricultural Systems cheat sheet

Agricultural Systems

• Agricultural systems are classified by inputs, outputs, and management intensity: subsistence, commercial, intensive, extensive, organic, and integrated systems.

• Crop rotation reduces soil-borne pathogen buildup and interrupts pest life cycles; legumes in rotation fix atmospheric nitrogen via Rhizobium symbiosis.

• The nitrogen cycle in farm systems: fixation, mineralization, nitrification, immobilization, denitrification, and leaching; ammonium and nitrate are the plant-available forms.

• Liebig's law of the minimum: yield is limited by the scarcest essential resource, not by total resource abundance.

• Integrated pest management (IPM) ranks controls as cultural, biological, mechanical, then chemical, with economic threshold as the spray decision rule.

• Soil texture triangle classifies soil by percent sand, silt, and clay; loam balances water retention and drainage for most field crops.

• Cation exchange capacity (CEC) measures a soil's capacity to hold exchangeable cations (K+, Ca2+, Mg2+, NH4+); higher CEC means greater nutrient retention.

• Water-holding capacity rises with clay and organic matter content; organic matter also improves aggregate stability and infiltration.

• Sustainable systems balance profitability, environmental impact, and social acceptability; indicators include soil organic carbon, nutrient use efficiency, and biodiversity.