Energy and Agriculture

Not since before the agricultural revolution has production of agricultural and forestry goods been without external inputs. Indeed, the natural fertility of the land, the hydrologic cycle, and solar radiation provide essential and large wssrm.

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Projected changes in agricultural productivity 2080 to climate change, incorporating the effects of carbon fertilization -50%_-15% 0 +15%

Figure 23.1 Projected changes in agriculture productivity in 2080 due to climate change, incorporating the effects of carbon fertilization (http://maps.grida.no/go/graph-ic/projected-agriculture-in-2080-due-to-climate-change). Data from Cline (2007); map designed by Hugo Ahlenius (UNEP/GRID-Arendal).

Projected changes in agricultural productivity 2080 to climate change, incorporating the effects of carbon fertilization -50%_-15% 0 +15%

Figure 23.1 Projected changes in agriculture productivity in 2080 due to climate change, incorporating the effects of carbon fertilization (http://maps.grida.no/go/graph-ic/projected-agriculture-in-2080-due-to-climate-change). Data from Cline (2007); map designed by Hugo Ahlenius (UNEP/GRID-Arendal).

natural inputs of nutrients, water, and energy. However, inputs of fertilizers and the widespread use of irrigation have enabled land productivity rates at levels much higher than natural inputs alone would provide. Science and technology have also played important roles to raise yields through the introduction of hybrid plants, some of which now require more nutrient and water inputs than their natural equivalents. The control of pests and weeds also requires large inputs of pesticides and herbicides. Many of the most critical inputs, such as nitrogen fertilizers, irrigation, and pesticides, are manufactured from or depend on fossil fuels.

Land productivity is also enhanced through the use of machinery, which has for many decades increasingly replaced human and animal labor while consuming large amounts of energy. Irrigation systems consume as much as 70% of all water consumption by agriculture, and the energy required to raise water from ground deposits or to move it from source regions to the fi eld can be considerable. Energy and water use has evolved with agriculture and forestry at a time when both were abundant and inexpensive, and their use has typically been wasteful and inefficient. For instance, some irrigation systems in semiarid zones, which could be more efficiently served by trickle irrigation, are instead flooded with large quantities of water that is lost to runoff or evaporation.

Generally speaking, large energy inputs to agriculture and forestry have been a management strategy for raising overall production rather than for maximizing energy use efficiency. Consider Figure 23.2, based on updates of the analysis of Gever et al. (1986), which shows an input-output analysis of the U.S. industrial agriculture system. It plots inputs in energy units and outputs in energy units (e.g., inputs of energy embodied in fuel and fertilizers, outputs in terms of caloric values). The figure is exemplary. The shape of this curve reflects a marginal return curve where every additional input raises overall output but at a diminishing rate, or decline in efficiency. Also shown on this curve is the approximate history of U.S. agriculture, as it increased inputs and raised outputs over time, from the 1940s to the late 1990s. The trend is clear: Total output of the agriculture system increased consistently, but at declining efficiencies.

Figure 23.2 Energy efficiency of industrial agriculture (Gever et al. 1986).

This situation in the U.S., which is similar to all industrial agriculture systems around the world, presents a modern paradox related to highly mechanized agriculture using large quantities of inputs: To achieve high outputs, large quantities of inputs are required. However, large outputs—bumper harvests— result in low market prices. Thus, producing a crop at the top end of this marginal return curve, with maximum output and maximum inputs, translates into a production system that is increasingly expending more money for inputs and receiving less money from outputs. In fact, one explanation for the so-called farm crisis in the U.S. in the late 1980s was a trap that farmers experienced as they were caught between falling prices and rising input costs (due in part to the price of energy and the increased usage), resulting in very low economic returns and the failure of many farm operations.

Still, focusing on the tradeoff between total production and efficiency of production can lead to simplistic conclusions about measuring sustainability. Consider, for instance, a continuum of different farming systems: from shifting cultivation to industrial agriculture. The former has very high input-output efficiencies, while the latter has very low input-output efficiencies. Yet the level of production (output) of a shifting cultivation will never be high enough to support current and future populations. Thus there is a need to optimize, or balance, both efficiency and total output in agriculture and forestry.

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