Timing of harvesting reverses the effect of twice cutting with ratoon rice

Introduction

The cultivation of rice using ratooning has several advantages over conventional cultivation, including lower costs, lower labor intensity, and lower greenhouse gas emissions (Sacks, 2013; Safruddin, 2017). A new practice for ratooning rice crops using the lower nodes of rice stubble, known as the SALIBU system, is gradually spreading throughout the tropical regions (Fitri et al., 2019; Yamaoka et al., 2017). The practice involves harvesting most of the above-ground portion of the plant but leaves the growing shoots intact. The SALIBU method implements 10 additional management practices to conventional management of rice cultivation in Indonesia. (1) early harvesting, (2) pre-fertilization (at seven days before harvesting), (3) cutting twice (rice was harvested 25 cm above the ground, then cut again at 3–5 cm above ground), (4) late irrigation (irrigation was started on day 14 after harvesting), (5) hand weeding, (6) dividing (dividing hills into two or three tillers and replanting to fill the space), (7) pushing (pushing the rice plants into the soil if the root came up on the soil surface), (8) removing excess plants (to keep original plant density), (9) draining from day 29 to 43 after harvesting, and (10) draining for the above (5) to (9) treatments. However, this new methodology has yet to be well studied. Oda et al. (2019) evaluated the Cohens’ d effect size (Cohen, 1992) of each practice in the technology package and clarified that the process of cutting twice has a large effect. Interestingly, the effect can be reversed depending on the management conditions. There is a large positive effect when poor management conditions are used but a medium negative effect when standard management conditions of direct seeding triple-cropping rice in the Mekong Delta are employed. The poor management conditions consisted of not using fertilizer, continuous-flooding water management, and late harvesting. There an interaction between the management conditions and the practice of cutting twice; however, which of the three conditions was responsible for the interaction has not been clarified. We assumed that it was late harvesting. Therefore, we examined the relationship between delayed harvesting and the number of ratoons under conditions with and without fertilizer. The results showed that the interaction does arise from the delay in harvesting.

Methods

A relationship between delayed harvesting and the number of ratoons was analyzed. We harvested rice plants grown under conditions of both with and without fertilizer. Rice was harvested on the day when 75% of the seeds on the main stems turned yellow (days 0), and after on days 4, 8, and 14. The water management approach we adopted was alternative wet and dry (AWD). Note, SALIBU practices are not used in this experiment.

Results

Effect of fertilizer

The application of fertilizer did not reverse the number of ratoons. There was a greater number of ratoons with fertilizer than without fertilizer; the response to delayed harvesting showed the same tendency (Figure 1a).

Figure 1. Effect of fertilizer and delayed harvesting on cutting twice.

•: fertilized, Δ: unfertilized. Bars represent 95% CI (n = 4). Rice was harvested on the day when 75% of the seeds on the main stem turned yellow (the standard SALIBU method; days 0), and after on days 4, 8, and 14. Rice was harvested at 25 cm aboveground first, then cut again at approximately 5-cm aboveground on day 7 after each harvesting.

Discussion and conclusion

Oda et al. (2019) show cutting twice can have a large effect on the number of ratoons; however, the effect can be reversed by different management conditions, such as adding fertilizer, delaying harvesting, or changing the type of water management used. We performed a pot experiment to investigate the effects that the level of fertilizer and the delay in harvesting time had on the number of ratoons.

Our results showed that the application of fertilizer does not reverse the effect of cutting twice on the number of ratoons. However, the timing of harvesting can reverse the effect of cutting twice on the number of ratoons. The number of ratoons continuously increased until the rice plants lost all of their living leaves. However, the second cutting conducted on the rice plant harvesting on days 0 resulted in no ratoons. By contrast, the single cutting normally gets ratoons. This means that cutting twice reduces the number of ratoons. Previous work also shows that cutting twice reduces the number of ratoons (Shiraki et al., 2020).

Harvesting earlier than normal (at the physiological maturing stage) is emphasized in the SALIBU technology package; however, our results showed that the second cutting is not advantageous when harvesting at the recommended timing. This is a significant finding for ratoon rice cultivation. The practice of cutting twice originated the custom of conventional harvesting of which cutting height is high. That should be distinguished from using lower nodes of stubble. In other words, twice cutting is recognized as an essential practice in SALIBU (Fitri et al., 2019; Yamaoka et al., 2017) but twice cutting is unnecessary when we can cut rice plant stems near the soil surface at harvesting. The use of a second cutting can have a large effect on the number of ratoons, so further studies should be conducted.

Data availability