Nitrogen uptake by deepwater rice during the preflood and flooded phases, in relation to drymatter and grain production uri icon

abstract

  • Crop response to N was affected particularly by time and severity of flooding. Deep flooding before plants were 50 days of age reduced N uptake and dry-matter production to low levels. Maximum water depth was around 1 m. In two trials, early fertilizer N ensured survival with rapidly increasing floodwater. Late N gave initially high plant N% and rates of uptake. Most treatments showed a sharp decrease in uptake immediately after flooding, but in two seasons the crop at Huntra had increased rates of N uptake during the later part of the flood, indicating continuing availability of N. The source of this N is yet to be identified. but crop uptake in the absence of fertilizer can integrate inputs of N from all other sources, and may be useful for predicting N requirements. Grain-yield was reduced if dry-matter was less than 1.50 t ha-1 or N uptake less than 20 kg ha-1 at the onset of flooding.
  • Deepwater rice (DWR) grows on rainfed dryland or with shallow flooding for 1-3 months, and is then flooded over 0.5 m for a month or more. In some areas, water may reach 4 m. Survival depends on elongation of stems, and panicle emergence occurs at about maximum water level. Most fields drain before harvest. Nitrogen balances are not known, and grain-yield responses to N are inconsistent due to the crop's long growth duration, extremes of drought and deep flooding, its sprawling growth habit and prostate condition at harvest, the possible movement of N with floodwaters, and unknown contributions of N from floodwater and biological fixation.
  • To assess the fate of applied N, we measured N uptake of DWR at two sites in Thailand: at Huntra, where soil with pH 5.5 usually has no grain response to added N; and at Prachinburi, with soil pH 4.0, where responses commonly occur. Fertilizer treatments were single application or split combinations of urea N as basal incorporation, broadcast three weeks after emergence or pre-flood, and super granules placed in the soil at the commencement of flooding, with rates of 37 or 75 kg N ha-1 in 1986 and 1987, and 56 kg N ha-1 in 1988. Plants were sampled for dry-weight and N content at intervals from before flooding to harvest.

publication date

  • 1991
  • 1991
  • 1991