Agriculture Reference
In-Depth Information
The use of manure and other forms of organic wastes should be highly encouraged
and practiced. As already discussed, there is growing concern about the changes to
the global nitrogen cycle being caused by synthetic N fertilizers and the effect this
might have on human health and the environment (Townsend et al. 2003). The recy-
cling of as much N as feasible could reduce the need for synthetically produced N
substantially. Perhaps as important, or even more so, is the recycling of P. Unlike
N, which has no limit to the amount that can be synthesized as long as an energy
source is available, commercial P fertilizer is manufactured from phosphate rock
obtained from underground mines and is a finite resource. As recent as 1950, about
80% of the P used for fertilizer globally was from organic sources, whereas about
90% today comes from phosphate rock (Cordell et al. 2009). Although the amount
of phosphate rock present globally is not known, the supply is finite. Cordell et al.
(2009) estimated that peak production of phosphate rock known to be economically
available for mining and processing would occur between 2030 and 2040; more
recent estimates have been revised upward (Jasinski 2011). Compared to the estimate
of about 16 billion Mt by Jasinski (2011), the International Fertilizer Development
Center estimated reserves as 60 billion Mt and would be sufficient for 300 to 400
years (Syers et al. 2011). Regardless of the amount, the fact that phosphate rock is a
finite resource and an element that is essential for food production requires recycling
for long-term sustainability. Cordell et al. (2009) estimated that only one-fifth of the
phosphorus mined in the world is consumed by humans as food.
4.7 CONCLUSIONS
While the production and sales of organically grown foods continue to increase at
significant rates, they still account for only about 2% to 3% of the total. There is
ample evidence showing that the yields of organically grown crops can be as high,
or even higher, than conventionally grown crops. Although consumers of organic
products generally consider the quality to be higher and also safer, the scientific evi-
dence to support these views is limited at best, particularly in developed countries.
While there is every reason to think the production of organic foods will continue
to increase, there is little likelihood that it will ever be a major source of the world's
total food supply. With a few exceptions, agricultural scientists suggest that world
food needs can only be met with the use of commercial fertilizers, and that even with
their use, the task will be challenging in view of increasing world population and
changes in diets that increase the demand for grain. At the same time, an increasing
number of scientists believe that changes in the global nitrogen cycle are becoming
so serious that major changes must be made in the fixation and use of atmospheric
nitrogen. Many long-term experiments have shown that the combined use of organic
materials and commercial fertilizers results in the highest yields and the best soil
quality. Therefore, every effort should be made to recycle nutrients to the fullest
extent feasible. This will not be easy because commercial fertilizers have historically
been relatively inexpensive, easy to use, highly concentrated, free of weed seed, and
of known composition of single or multiple nutrients. In contrast, organic materials
such as manure are highly variable in terms of moisture, concentration and availabil-
ity of nutrients, kind and number of weed seed, ease of handling, and uniformity of
Search WWH ::
Custom Search