Potential of Controlled Irrigation and Drainage for Reducing Nitrogen Emission from Rice Paddies in Southern China

Table 1

Design of controlled irrigation and drainage (CID) scheduling.

Treatments	Tillering stage	Jointing-booting stage	Panicle initiation stage	Milky stage
T1	120 mm (10 d)	−300 mm~30 mm	−300 mm~30 mm	−300 mm~30 mm
T2	−200 mm~20 mm	250 mm (10 d)	−300 mm~30 mm	−300 mm~30 mm
T3	−200 mm~20 mm	−300 mm~30 mm	250 mm (10 d)	−300 mm~30 mm
T4	−200 mm~20 mm	−300 mm~30 mm	−300 mm~30 mm	250 mm (14 d)
CK	−200 mm~20 mm	−300 mm~30 mm	−300 mm~30 mm	−300 mm~30 mm

Note: − mm~ mm denotes that water depth was kept between – mm and  mm at four stages of paddy rice at normal time; when water level lowered to − mm, irrigation water is added until water table reached  mm.  mm ( d) indicates that  mm fixed water level was kept with duration of days at four stages of paddy rice from the soil surface. The allowable variation of fixed water level was ±5 mm during the period of implementation. The maximum water height after rainfall for the control is 50 mm at the tillering stage and 100 mm at other stages. When rainfall increased water depth beyond the designed value, drainage occurs. 4 mm water leakage per day was kept when water table existed at soil surface. AWD indicates alternate wetting and drying irrigation; CID-Stage  I, CID-Stage  II, CID-Stage  III, and CID-Stage  IV denote the CID treatments at tillering stage (Stage  I), jointing-booting stage (Stage  II), panicle initiation stage (Stage  III), and milky stage (Stage  IV), respectively.