Facts and Myths of Feeding the World with Organic Farming Methods - Principles of Sustainable Soil Management in Agroecosystems - page 96

More recently, Brandt et al. (2011) concluded that organic crops contain significantly
higher levels of secondary metabolites (compounds that are believed to protect peo-
ple against a range of diseases including obesity) than conventionally grown crops.
High nitrogen availability generally results in increased protein synthesis. Thus,
when N fertilizers are added to fields where grain crops are produced, these grain
crops often, but not always, have higher crude protein than organically grown crops.
Magkos et al. (2003) reported that organically produced grains had higher concen-
trations of some of the essential amino acids, but there was no clear picture. Data for
comparisons of vitamins, minerals, and trace elements were too limited to draw any
conclusions. More recently, Dangour et al. (2009) surveyed 52,471 articles, identi-
fied 162 studies (137 crops and 25 livestock products), and selected 55 as having
data of satisfactory quality for further comparisons. From an analysis of the data
from these selected studies, they concluded that conventionally produced crops had
a significantly higher content of nitrogen, and organically produced crops had a sig-
nificantly higher content of phosphorus and higher titratable acidity. No evidence of
a difference was detected for the remaining 8 of 11 crop nutrient categories analyzed.
Analysis of the more limited database on livestock products found no evidence of
a difference in nutrient content between organically and conventionally produced
livestock products.
4.3 LIMITATIONS OF ORGANIC FARMING
The previous sections have shown that organically grown crops can be similar to
those produced using chemical fertilizers, and at least equal or superior in terms
of quality and safety. The real question with regards to organic agriculture is to
what extent the food and fiber needs of the world population can be produced with-
out the use of chemical fertilizers. The world population is presently 7 billion and
expected to reach 9.2 billion by 2050. Protein consumption is essential for humans,
and the concentration of N in protein is approximately 16%. Smil (2002) states that
published recommendations for ideal protein requirements were 3-4 g/kg of body
weight for infants, 1.5-3 g for teenagers, and 0.3-1 g for adults. Smil (2011) esti-
mated that global consumption of N contained in food was 30 Mt and essentially all
of this is excreted. Furthermore, since more than 50% of people on all continents,
except Africa, now live in cities, most of this waste is released directly into sewers.
Most of the sewage water is either released to streams or coastal water and little is
ever recycled for crop production. Therefore, a tremendous quantity of N is lost from
human consumption, and there are also large losses of N each year from animals.
These losses must be balanced by inputs to sustain the system. There are natural
ways for providing N for crops that have been long known. Von Liebig (1840) listed
three ways: (1) recycling of organic wastes (mainly crop residues and animal wastes);
(2) crop rotations including N-fixing leguminous species; and (3) growing legumi-
nous cover crops and plowing them under as green manures. While all of these can
provide N to growing crops, only the N fixed from N 2 in the atmosphere by symbi-
otic bacteria associated with leguminous crops is added. Other sources of added N
for crop production are atmospheric deposition and irrigation waters from aquifers.
Ladha et al. (2005) estimated that additions to crop production from atmospheric