Table 6. Locations, climate conditionsa and initial surface soil properties (in 1990) at the long-term experiment sites.
| Variables | Urumqi | Yangling | Zhengzhou | |
|---|---|---|---|---|
| Latitude | N | 43°49´ | 34°17´ | 34°46´ |
| Longitude | E | 87°36´ | 108°03´ | 113°39´ |
| Altitude | / m | 600 | 523 | 59 |
| Annual mean temp. | / oC | 7.3 | 13.5 | 14.7 |
| Cum. E.Tb for winter wheat | / oC | 2603 | 2115 | 2400 |
| Cum. E.T for spring wheat | / oC | 1865 | — | — |
| Cum. E.T for maize | / oC | 3232 | 2889 | 3056 |
| Annual precipitation | / mm | 299 | 585 | 641 |
| Precip. for winter wheat | / mm | 248 | 216 | 213 |
| Precip. for spring wheat | / mm | 126 | — | — |
| Precip. for maize | / mm | 172 | 369 | 427 |
| Annual mean irrigationc | / mm | 450 | 270 | 225 |
| Annual open pan evaporation | / mm | 2015 | 1292 | 1808 |
| Cropping system | Mono | Double | Double | |
| Crop rotation | Wheat-maized | Wheat-maize | Wheat-maize | |
| Plot size | / m2 | 468 | 196 | 400 |
| Soil classification (FAO) | Haplic Calcisol | Calcaric Regosol | Calcaric Cambisol | |
| Parent material | Limestone | Loess | River Alluvium | |
| Clay (<0.002 mm) | / % | 20.4 | 21.0 | 10.1 |
| Silt (0.002–0.05 mm) | / % | 44.0 | 73.6 | 57.3 |
| Sand (>0.05 mm) | / % | 35.6 | 5.4 | 32.6 |
| Soil pH | 8.1 | 8.6 | 8.3 | |
| Bulk density (0–20 cm) | / g cm−3 | 1.21 | 1.35 | 1.41 |
| Bulk density (20–40 cm) | / g cm−3 | 1.35 | 1.56 | 1.44 |
| SOC (0–20 cm) | / g kg−1 | 8.8 | 7.44 | 6.7 |
| TN (0–20 cm) | / g kg−1 | 0.87 | 0.93 | 0.67 |
aData are means over 1981–2010 from the China meteorological sharing service system ( http://cdc.cma.gov.cn/).
bCum. E.T: cumulative effective temperature above 0 °C.
cBased on Zhao et al.40.
dCrop rotation at Urumqi during 1990–2009 was as follows: maize in 1990, 1993, 1996, 2000, 2003, 2005 and 2008; spring wheat in 1991, 1994, 2002 and 2006; winter wheat in 1992, 1995, 1997, 1998, 2001, 2004, 2007 and 2009; and cotton in 1999.