Alternative Nitrogen Sources for Organic Rice Production.

Nitrogen (N) is the most limiting nutrient in irrigated organic rice production. Poultry litter (PL) has been the primary source of N fertility in California's organic rice systems, however, its availability is uncertain, its nutrient composition is low and variable, and the timing of nutrient release may be  inconsistent. Field trials were conducted during the rice growing season in 2008 and 2009 in the Central Sacramento Valley in order to evaluate the performance of three pelletized organic fertilizers, and PL in supplying the N needs of the crop under continuously, and non–continuously flooded conditions. The trials were conducted using a randomized complete block design, and were planted with an N-responsive rice variety (S-102), with different fertilizers as treatments, applied at the same rate of 157 kg N ha^-1 (2008) and 134 kg N ha^-1 (2009) in treatment plots. Control plots received zero N, and phosphorous and potassium were applied to all plots to ensure that these nutrients were not liming.                                               

All fertilizer N became available to the plants before panicle initiation based on mid-season plant N uptake data. N supplied through the commercial organic fertilizers was more available than PL, which had the lowest plant N uptake at harvest in all field sites, averaging only 18 kg N ha^-1 higher than the plant N uptake in control plots. Overall, plots treated with PL had the lowest yields of the fertilizer treatments averaging 8,448 kg ha^-1 to 10,384 kg ha^-1 across sites,  and the lowest N use efficiency averaging 19 % to 21 % across sites.  All fertilizers were least effective in fields that underwent an extended drain for weed control. Further research is needed in order to formulate recommendations on the optimal application rates for these products under various management systems in organic rice production.