Table 1. Organic matter, total N, P, and K content of soil mixtures used in 2007, 2008, and 2009 rice root experiments.

Year	Organic matter (g·kg–1)	Total N (g·kg–1)	Olsen-P (mg·kg–1)	Exchangeable K (mg·kg–1)
2007	12.8	0.86	10.2	105.2
2008	12.2	0.92	9.2	108.8
2009	13.6	1.12	11.1	112.4