Trends in Moisture Index, Farmland Area, and Their Combined Effects on Grain Production in Northern China

Table 6

Factors that affect grain yield.

County	Year	Unit grain yield (kg/ha)	Cropping index	Chemical fertilizer applied (kg/ha)	Total power of agricultural machinery (W/ha)	Percentage of irrigated area (%)
Juxian	1989	4,635	1.22	304.3	2,648.2	53.9
	2008	6,382.6	0.78	1455.5	10,166.2	50.0
Yuxian	1989	809.8	0.75	65.1	688.3	25.4
	2008	911.0	0.73	106.9	3,453.0	35.0