Nitrogen and Water Management Effects on Spikelet Sterility of Flooded Rice in Chile.

Spikelet sterility (blanking) due to low temperature during reproductive stages is one of the most limiting factors for rice production in Chile. Accepted losses are usually 10% but in cold seasons they can get up to 100%.
The present work had for objective to evaluate the effect of nitrogen (N), water management, and the use of a growth regulator on spikelet sterility of four rice varieties grown under flooded conditions.
Experiments were performed at the location of Parral (36º 1’ 42’’ south latitude,  71º 54’ 23’’ west longitude) on a Vertisol soil that has been continuously cropped with rice in a rice-fallow (2 years) rotation.
Nitrogen treatments consisted on four N rates: 0, 60, 120, and 240 kg N ha^-1, applied as urea (46% N) in two equal splits at planting and early tillering, respectively. Water treatments consisted on two water heights from panicle initiation: 5 and 15 cm. Other evaluated management factor was the application of a growth regulator (trinexapac ethyl): 0 and 300 ml ha^-1, at panicle initiation.
Evaluations included: viable pollen count at anthesis, SPAD readings and N content at flag leaf, yield and yield components, and percent blanking at harvest. Besides, air and water temperature were measured during the whole season (November-March) at 15-minute interval, using a wireless sensor system. Pollen viability was evaluated by dissecting anthers and staining pollen grains with potassium iodine (KI). Total and viable pollen count was done by imagery analysis.
Results indicated that all evaluated factors affected spikelet sterility. Large differences on pollen viability were observed among varieties and evaluated management practices.
Results of the effects of the evaluated management practices on blanking and rice yields are discussed.