The trail was initiated in Spring 2000 on a silt loam soil (Udic Dystocrept, USDA) in Canterbury, New Zealand and includes a combination of crop and tillage treatments: permanent pasture [PP], permanent fallow [PF], rotation of barley, wheat and peas under intensive [Ii], minimum [Mm] and no tillage [Nn].
A long-term (over 20 years) experimental field study, started in 1989, was conducted to investigate the changes in soil Se fractions and its uptake by crops, as affected by different fertilizer practices, in the North China Plain with an annual crop rotation of winter wheat and summer maize.
In this study, three seasons rotation (wheat-guar-wheat) experiment was conducted from 2008 to 2010 on a sandy clay loam, hyperthermic, mixed, gypsic cambiorthid, nonsaline, with organic matter of less than 1%% (Table 1).
The common 3-year rotation of oilseed rape, wheat, winter barley was employed by one grower on 10 of their fields, for which significant spatio-temporal heterogeneity was shown by the proposed randomisation test.
The model analysis verified that groundwater tables in the region are subject to steep declines (up to 1 m/yr) due to decades of intensive exploitation of the groundwater resources for crop irrigation, primarily the widespread crop rotation of irrigated winter wheat and mostly rainfed summer maize.
According to the study by Han et al. (2005) in Zhaoguang Farm, which was the first mechanical farm built in Heihe city in late 1950s, the vegetation has changed from natural vegetation to cropweed, to rotation of corn-soybean-wheat, or to rotation of corn-soybean.
Wheat has been grown in these fields in rotation with cotton and the cultivation of wheat can select for certain fungal genotypes (Edel et al. 1997).
Table 2 Date of sowing and harvesting of wheat and guar in the rotation Crop Sowing Harvesting Wheat 18/11/2008 18/2/2009 Guar 9/7/2009 30/9/2009 Wheat 13/11/2009 10/2/2010 Fallow period range between 3 and 5 months.
