I think Madurobob makes a very good point.
In Gettman's report:
http://www.drugscience.org/Archive/bcr2/MJCropReport_2006.pdf
Mr Gettman makes several assumptions, and I cant figure out where he got his numbers.
He makes a value assumption of $1606/lb
He states a 7 oz/per plant harvest assumption, but then the numbers he shows represent the DOJ's assumption of 1 lb/plant.
He states that seizures of outdoor cultivated marijuana represent only 8% of all outdoor cultivated plants, and that indoor cultivated plant seizures represent by 2% of all indoor plants, but then makes an overall production estimate of 10,000 metric tons, which jibes with the DOJ estimate (based on a 30% eradication rate).
The department of Justice report 2007
http://www.usdoj.gov/ndic/pubs22/22486/22486p/22486p.pdf
DOJ statistics show 6.3 million plants eradicated in 2006
DOJ assumes 1 lb per plant, which then comes to 2825 metric tons of pot destroyed (which, if that represents 30% of total cultivated comes to 9478 metric tons)
DOJ indicates that eradication programs destroy between 30-50% of all cultivated marijuana
DOJ estimates overall production from 5650 to 9417 metric tons
DOJ quotes prices as $700 - $750 per lb for outdoor cultivated pot
high potency indoor cultivated sold for $2500 - $6000 per lb
From Norml's website:
http://norml.org/index.cfm?Group_ID=4444
It should be noted that law enforcement's model when estimating marijuana's weight and value differs from the above paradigm. Drug Enforcement Administration (DEA) officials have long argued that a typical marijuana plant grown to harvest yields one pound (454 grams) of marijuana. However, most experts argue that this estimate is highly unrealistic. For example, data gathered by the United States Sentencing Commission supported the conclusion that the actual average yield of marijuana plants is 100 grams. [1] Government-sponsored studies conducted at the University of Mississippi calculated the amount of dry, smokable material at a maximum of 177 grams for an indoor marijuana plant and 412 grams for an outdoor plant. [2] The ten ounce estimate used by The NORML Foundation in this report reflects this data as well as the premise that most U.S. marijuana is densely grown in gardens of nine square feet or less. Under such conditions, DEA publications admit that one marijuana plant will likely yield approximately 224 grams of marijuana.
so... trying to work some of the same numbers
If 6.3 million plants eradicated represents 30% of total cultivated, that comes to around 20.9 million plants total cultivated.
20.9 million plants at 7 oz/plant (Gettman's figure) harvested = 7.3 million pounds = 3310 metric tons
7.3 million pounds x $1606/lb = $11,723,800,000 ($11.7 Billion)
20.9 million plants at 10oz/plant (Norml's figure) = 13 million pounds = 5924 metric tons
13 million pounds x $1606/lb = $20.8 Billion
Of course, the figures aren't really true, because 30% or more of the crop was actually destroyed. Assuming it was 30%, the actual "cash crop" for 2007 was around 14.6 million plants worth somewhere between $8.2 billion and $14.5 billion
According to
http://www.bloomberg.com/apps/news?pid=20601087&refer=home&sid=aSVTuzqlzaEQ
Corn is the biggest U.S. crop, valued at a record $52.1 billion in 2007, followed by soybeans at $26.8 billion. Wheat was in fourth place, behind hay, with a value of $13.7 billion.
So, in conclusion, pot isn't really the number one cash crop. It's actually third or lower, depending on how you value it. Not so much headline worthy, really.