Crop production in some of the most intensely cultivated regions involves a trade-off between maximizing yields and degradation of the environment. As fertilizer application increases, crop yield has diminishing returns, but nitrate leaching increases exponentially (Figure 5.7). An increase in nitrogen from the Mississippi Basin has led to eutrophication in the Gulf of Mexico (Goolsby et al. 2001). This implies that by reducing fertilizer use slightly in some of the most heavily fertilized regions, one could see major gains in terms of nitrate pollution, and compensate this by increasing fertilizer use in some of the less fertilized regions to increase production without big consequences for eutrophication. Moreover, some measurements indicate that in the U.S. a few farms contribute to a majority of the high fertilizer application rates, so one could target these farms without major losses in production to avoid nitrate leaching into the Mississippi River. Such trade-offs could be sought with respect to other ecosystem services involving use of the land (Foley et al. 2005; DeFries et al. 2004). A typical example is that of agricultural land in the central U.S. Here, the land is productive largely because of nitrogen- and phosphorous-rich fertilizer, manufactured through substantial inputs of energy and enabled by NRRs such as copper and steel. If fertilizer is overused, as is often the case,
Fertilizer application Figure 5.7 Targets for fertilizer reduction.
a portion of it is lost to nearby rivers, causing degradation of water quality (Raymond and Cole 2003; Simpson et al. 2009).
Increasing Yields and Optimizing Agricultural Production
Productivity of existing cropland can be improved, although regions differ with regard to their potential to increase yields and optimize production. Large potentials for increased yields of food and nonfood biomass seem to exist, for instance, in Sub-Saharan Africa, where agricultural development is hampered by grossly inadequate investments in infrastructure, production capacities, education, and training. There are promising local examples of how improvements can be managed, also to the benefit of the rural population. In countries with high crop yield levels, a constraint of rising importance is the increasing level of nutrient pollution. Adjusting crops and cultivation methods to local conditions and promoting good agricultural practice may provide opportunities for efficiency increases and reduction of environmental load.
The land-intensive nature of meat production suggests that pressure on land could be greatly alleviated by transitioning to a less meat-intensive diet. The opportunities are immense. If today's livestock grain were fed directly to people, and assuming a 1:5 average efficiency for meat consumption compared to grain consumption, we could feed 9.4 billion people (compared to today's world population of 6 billion). Thus, the world population could grow to 9-10 billion people, if they were to transition to a completely vegetarian diet, without adding additional pressure on the land. Alternately, we can estimate that 36% of today's cropland (or 540 million km2) would be freed up for uses other than agriculture if the current population were to transition to a completely vegetarian diet.
Considerable potentials for energy recovery from municipal organic waste and residues in agriculture and forestry exist. For example, the energetic use of wastes can provide the double benefit of waste management and energy provision. Residues from agriculture, forestry, and biomass-processing industries have great potential as feedstocks for stationary energy provision. To a more limited extent, second generation technologies for transport biofuels, when these become available, could also make use of residues. Energy recovery from waste and residues can save significant greenhouse gas emissions without requiring additional land. However, research is required with regard to the proper balance of residues remaining on the field for soil fertility and removal for energy, as well as with regard to nutrient recycling after energy recovery.
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