By Jarrod Hardke, Rice Extension Agronomist
Hybrid rice cultivars currently make up 40-50% of Arkansas rice acreage on an annual basis. Harvest aids, specifically sodium chlorate, are applied to an estimated 40% of total rice acres. Previous work on sodium chlorate in rice in Arkansas focused primarily on long-grain varieties. To date no work has been conducted on hybrids.
Current research ongoing in 2018 involves RiceTec XP753 – comparing a 6 lb ai/acre rate of sodium chlorate versus no harvest aid. Also evaluated was the time of harvest – 3 days after application or 7 days after application. The effects on grain moisture reduction and grain yield are presented in Figures 1 and 2. Additional data is forthcoming as we make more applications. Milling yields will also be evaluated once samples are dried.
The general take-home is that we achieved a significant moisture reduction in just a few days after application (Fig. 1) whether harvest occurred 3 or 7 days after application. This is consistent with previous work which has shown 3-5% moisture reductions in just a few days.
Figure 2 is the real kicker. When harvested 3 days after application, yield loss is minimal in the treated plots compared to the check. However, when harvest is delayed until 7 days after application, yield losses can be large, though not always significant in this study. Keep in mind that grain moisture at the time of sodium chlorate applications were high so far in this study (25%, 23%, and 22%). Applications at lower grain moistures are currently being made. That data will be added to these figures and shared as it becomes available.
Past research conducted on Wells did not show a significant yield reduction when applications were made at 18-25% moisture, but did show a dramatic reduction in head rice milling yields when harvest was delayed 6 or more days after application. Pilot study milling data on XP753 last year suggested that head rice yields could be reduced when sodium chlorate was applied to rice at 24% and 21% grain moisture, but not at 18% and 17% grain moisture.
While more research is needed on the proper timing of sodium chlorate to hybrid rice, this initial research suggests that the window of application may be more restrictive than our current recommendation of 25-18% grain moisture.
Fig. 1. Effect on harvest grain moisture of sodium chlorate applications to XP753 hybrid rice.
Fig. 2. Effect on grain yield of sodium chlorate applications to XP753 hybrid rice.
Fig. 2. Harvest aid trial on XP753 – 7 day post-treatment (left), 3 day post-treatment (center), and untreated (right).