Nitrogen Availability Strongly Affects Productivity of Ratoon Rice Plants

Warming trends and concomitant increases in frost-free period are expected to alter cropping systems and subsequent land productivity in temperate climate regions. Our agricultural and food systems need to adapt to such changes. Here, we examined how nitrogen (N) availability would affect productivity of rice double cropping in combination with its ratoon regenerated from their parents rice plant (Oryza sativa, cv. Jomyeong) with early maturing habit. For main cropping season, rice plants were transplanted in experimental paddy field (35°10'N, 26o53'E, alt. 33.0m) of Chonnam National University, on April 25, 2016, and grown under local farmers' agronomic practices. After main crops harvested on August 17, ratoon rice plants were grown at five different levels of N availability [0 (N0), 9 (N9), 18 (N18), 28 (N28) and 37 (N37) kg N ha-1] and harvested on November 20. Unexpectedly, plant height of ratoon rice was unaffected by N availability. However, aboveground biomass (AGB) and yield of ratoon rice were significantly affected by N availability, displaying an increase of 56.5 kg ha-1 and 26.3 kg ha-1 per unit (1 kg ha-1) increase in N fertilization, respectively. As a result, while at N0, the AGB and yield of ratoon rice plants were 4.14 Mg ha-1 and 1.46 Mg ha-1, respectively, they increased to 6.32 and 2.35 Mg ha-1 at N37, corresponding to 47% and 41% of those (i.e. 13.39 Mg ha-1 in AGB and 5.68 Mg ha-1 in yield) of main rice plants. Under high N availability, the greater number of regenerated tillers and panicle per m2 contributed to greater ratoon rice productivity. Combined annual productivity of the main and ratoon seasons ranged from 17.5 to 19.7 Mg ha-1 for AGB and from 7.1 to 8.0 Mg ha-1 for yield depending on N availability. The results suggest that ratoon rice double cropping could provide an ample opportunity to consolidate national food security in the warming world by increasing annual land productivity.