Title: Impact of organic production management on variety yield and grain arsenic accumulation Authors
Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 2, 2013
Publication Date: N/A
Technical Abstract: The demand for organically produced rice increases each year. Organic rice production offers economic benefits to growers because the crop can be sold at a premium and input costs are generally lower. The objective of this experiment was to determine the agronomic performance of rice cultivars grown under organic and conventional field management. The study was conducted in Beaumont, TX during 2009, 2010, and 2011 and evaluated 14 rice cultivars that included medium and long grains, aromatics, and allelopathic germplasm. The organic studies were conducted on certified organic land following a winter cover crop (white clover) that was plowed down in the spring followed by application of 1680 kg/ha of Nature Safe (13-0-0; made from feather, meat, and blood meal) applied at planting. The conventional fields were fallowed for two years and then drill seeded with 224 kg/ha of urea applied in a three way split. The experimental design consisted of a RCB with four replications. Data were collected on plant stand, heading, height, days to harvest, grainfill duration, yield, total and whole milling yield, and total grain arsenic. The main effects year, cultural management, and variety were significantly different for essentially all traits, as were their interactions. As had been seen in previous studies, rice grown under the organic system had reduced plant stands, earlier days to heading and maturity, a shorter grainfill period, and shorter plant height as compared to conventional management. Although there was no significant difference in head rice yields, organic management had significantly higher field yield, total milling yield, and total grain arsenic than the conventional system. There was a significant cultural management x variety interaction for most traits but correlations between the variety means under organic and under conventional management were generally >0.60, indicating similarities in varietal performance under either cultural system. Exceptions to this were plant stand, total milling yield, and total grain arsenic, which were not significantly correlated between the two cultural management systems. There were few significant correlations among the agronomic traits measured under the conventional system. However, under organic management, yield was positively correlated with maturity, height, and grainfill (r= 0.54, 0.76, 0.43, respectively). In the organic system, the highest yielding cultivars were Tesanai 2 (11035 kg/ha), Rondo (8690 kg/ha), PI 312777 (7928 kg/ha), PI 338046 (7925 kg/ha), and Wells (7870 kg/ha) while the lowest yielding cultivars were Colorado (5163 kg/ha) and Sierra (5139 kg/ha). When combining field yield with whole milling yield (i.e. whole milled rice per acre), the best performing cultivars under organic management were Jupiter (4973 kg/ha) and Tesanai 2 (4447 kg/ha), while Sierra (2566 kg/ha) and Colorado (2459 kg/ha) were the poorest. No trait was significantly correlated with grain arsenic under conventional management, however under the organic system, where there was a two-fold range in total grain arsenic of the milled rice, grain arsenic was positively correlated with height, maturity, grainfill, and yield (r= 0.47, 0.53, 0.57, 0.65, respectively). Sierra (0.09 ppm) and Colorado (0.11ppm) had the lowest grain arsenic accumulation under organic production, although they were also the lowest yielding. These results indicate that under organic management, agronomic traits associated with increased yield potential are also associated with greater grain arsenic accumulation. The varieties with the highest organic yields were all of indica origin (Tesanai 2, Rondo, and the two allelopathic germplasms, PI312777 and PI 338046) however, these also had moderate to high grain arsenic levels. Other research has shown that cultivars exist that accumulate low levels of grain arsenic (e.g. Zhe 733) even under arsenic (MSMA) treated soils and that draining rice fields during the growing season dramatically reduces grain arsenic levels. Under organic management, maintaining a season long flood is critical for weed control. A next step would be to determine if weed suppressive, allelopathic germplasm could be advantageous in an organic management system that incorporated field draining to reduce grain arsenic accumulation or if using germplasm that does not accumulate grain arsenic would be a better approach.