Part III - Production processes

Summary

The adequacy of agriculture as our source of food depends upon production rates in crops and pastures. This section considers the important ‘production processes’. It begins with production and cycling of nitrogen (Chapter 8). Nitrogen has key roles in the structure of proteins and nucleic acids and thus can be considered, along with carbon, as one of the central elements of life. Nitrogen is subject to complex cycling and its supply is frequently limiting to the performance of plant communities. Water is also commonly in scarce supply. Uptake of water from soils and its movement along the soil–plant–atmosphere continuum is the focus of Chapter 9, which gives particular attention to losses that occur through evaporation and transpiration. Acquisition of atmospheric carbon dioxide and its fixation and reduction (Chapter 10) are the central production process. Photosynthesis is closely coupled with partitioning (pattern of use) of reduced carbon in respiration and growth (Chapter 11).

Achievement of significant rates of photosynthesis depends upon large investments in the construction and maintenance of a foliage canopy supported by stems and roots. Photosynthesis further depends upon the existence of rapidly growing ‘sink’ tissues capable of utilizing large supplies of new organic substrates. The aim in farming is to find and culture plant materials in ways that tend to optimize partitioning for efficient use of scarce resources such as sunlight, water, nitrogen, and human effort.