Effects of Controlled Irrigation and Drainage on Nitrogen and Phosphorus Concentrations in Paddy Water

Table 1

Controlled thresholds in different stages for controlled irrigation and drainage (CID) in the year 2015.

Treatments	Tillering stage (stage I)	Jointing-booting stage (stage II)	Panicle initiation stage (stage III)	Milky stage (stage IV)	Period of water control
FDTF	−500~200	−200~50~200	−200~50~200	−200~50~200	Jul. 3–Jul. 12
	−200~20~100	−500~250	−200~50~200	−200~50~200	Jul. 29–Aug. 6
	−200~20~100	−200~50~200	−500~250	−200~50~200	Aug. 24–Sep. 2
	−200~20~100	−200~50~200	−200~50~200	−500~250	Sep. 16–Sep. 25
FFTD	200~−500	−200~50~200	−200~50~200	−200~50~200	Jul. 3–Jul. 14
	−200~20~100	250~−500	−200~50~200	−200~50~200	Jul. 29–Aug. 7
	−200~20~100	−200~50~200	250~−500	−200~50~200	Aug. 24–Sep. 4
	−200~20~100	−200~50~200	−200~50~200	250~−500	Sep. 16–Sep. 28

Note: − mm∼∼ mm denotes that water depth was kept between – mm and  mm at four stages of rice paddies at normal time; the maximum water height after rainfall for the control is  mm. When water level lowered to − mm, irrigation water is added until water level reached  mm.  mm∼ mm or  mm∼ mm indicates the controlled thresholds of water level in different stages. The allowable variation of fixed water level was ±5 mm during the period of implementation; 2 mm water leakage per day was adopted when surface water existed. FDTF indicates first drought and then flooding; FFTD indicates first flooding and then drought.