property>volume per unit area
What is Volume Per Unit Area?
As a physical property, volume per unit area is such a simple concept that it could be taken to mean many things. Its primary use is in agriculture where farmers use it as a way of measuring crop yields for a given area of cultivated land, although it could refer to any volume of something that comes from, or is applied to, an area. A widely used unit of measurement for crop yields is the number of bushels per acre. One bushel amounts to 0.04 cubic meters or 8 gallons. However, the bushel has recently gone out of fashion as a way of measuring volume. It is now considered to be more of a unit of mass, even though many still refer to crop yields as a volume per unit area of bushels/acre.
Due to recent technological changes, the average yield for many crops has gone up over the last hundred years or so. For example, in 1973, the average wheat yield in the United States was somewhere around 32 bushels/acre. By the year 2008, this number went up to around 45 bushels/acre. If one were to interpolate these values and determine a rate of change, it would amount to a change of 0.33 bushels of wheat/acre per year.
Corn has also undergone a dramatic growth in its volume yield per unit area ever since 1940. This is mostly due to advances in biotechnology. Before 1930, most corn was of the open pollinated variety. Now, almost all corn planted is from some kind of hybrid seed. In 1900, the average corn yield was 29 bushels/acre. By 1998, it had risen all the way to 134 bushels/acre. If we were to look at the average growth rate for corn between 1940 and the present day, it would amount to about 1.8 bushels/acre/year. The year 2009 portends to be yet another record year for corn growers, with an average corn yield at 153.8 bushels/acre. There was a contest amongst growers in 2009 to see who could get the highest corn yields, and one grower amassed 368 bushels/acre.