Principle components analysis of environmental and soil variables for agricultural soils in 19 counties within Henan Province.

<p>Length of arrows is directly proportional to their importance in explaining spatial patterns in the counties. Direction of the arrows indicates increasing values. Thus, the x-axis is primarily a gradient in soil C, whereas the y-axis is primarily a gradient in soil N and rainfall and secondarily a gradient in soil N. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109188#pone-0109188-t001" target="_blank">Table 1</a> for key to county name abbreviations.