Rice Cultivation by Direct Seeding into Untilled Dry Paddy Stubble

Research Paper EAEF 5(2): 65-, 2012 Rice Cultivation by Direct Seeding into Untilled Dry Paddy Stubble -Proposal of a New Seeding Method and Germination Rate with That- Yoshifumi NISHIURA* 1, Teruo WADA* 1 Abstract We propose direct seeding into the previous year s stubbles as a labor-saving rice cultivation method in untilled dry paddy fields. The effectiveness of this method was determined by conducting a seeding experiment. Three seeding holes at depths of 20 or mm were bored per stubble, and 4 or 7 seeds were sown per stubble. Four sets of experiments were designed with different combinations of seeding depth and seeding number, and each set of conditions was replicated 3 times. Germination rate and stubble width were determined 1 month after seeding. Our results suggest that seeding in stubbles may be effective in preventing bird damage typically noted in shallow seeding but that deep seeding restricts seedling growth through shielding of sunlight. [Keywords] direct seeding, germination rate, previous year s stubbles, rice, untilled dry paddy field, new seeding method I Introduction Three methods are currently used for direct seeding in rice cultivation: direct seeding in (1) flooded paddy fields, (2) tilled dry paddy fields, and (3) untilled dry paddy fields. For direct seeding in flooded paddy fields, rice seeds are directly sown in paddy fields that have been tilled, clod crushed, and soil puddled. Although this method removes the need for seedling transplantation, Calper coating of seeds is necessary to increase the germination rate (by increasing oxygen supply) (Okamura, 2001). With direct seeding in tilled dry paddy fields, the soil puddling process, which is necessary for direct seeding in flooded paddy fields, is not necessary, and rice seeds are sown directly into tilled dry fields. Because tillage is necessary when using this method, seeding or pest control is sometimes delayed due to rainfall. Over-wetted soils are often difficult to reduce into fine particles, causing poor germination and less healthy seedlings. For direct seeding of untilled dry paddy fields, rice seeds are sown into untilled dry fields. Rainwater flows easily over the untilled ground, resulting in a soil with good drainage and high bearing capacity. Because tillage, clod crushing, soil puddling, and transplanting processes are not necessary when using this method, it is considered to be the simplest and most labor-efficient method of rice cultivation. In this report, we propose a new method of seeding untilled dry paddy fields. The effectiveness of this method was determined by comparing the germination and seedling rates of rice seeds under various seeding conditions. II The Proposed New Seeding Method 1. Custom methods of direct seeding in untilled dry paddy fields and the associated problems In Japan, there are two standard methods for direct seeding of untilled dry paddy fields: the Okayama method and the Aichi method (Washio, 2003). The Okayama method prescribes that seeding, fertilizing, pesticide application, and soil covering are carried out in a ditch with a depth of 20 mm. The ditch is prepared using a reversibly rotating ditching machine equipped with soil-covering blades. The advantages of this method include stable germination, stable seedling growth, no disturbance of the seeding process by weather changes, elimination of the need of a water supply at the time of seeding, a high lodging tolerance, reduced bird damage, high soil permeability, low methane emission, good rice yield, and a quality comparable to that obtained by standard rice cultivation (Okatake, 1998). The distribution of seeds is nearly identical to that achieved with dibbled seeding, although strip seeding sometimes occurs when the seeding machine speed is increased. Strip seeding decreases both germination rate and lodging tolerance; hence, a relatively slow seeding speed is desirable (Kimoto et al., 1995). In the Aichi method, seeding and fertilizing are carried out in a V-shaped -mm deep ditch with an opening width of mm. The ditch is prepared using a ditching wheel. A characteristic of this method is that paddy fields are tilled and soil puddled in the winter in order to avoid a crowded *1 JSAM Member, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1, Gakuen-cho, Naka-ku, Sakai, Osaka, 599-8531 Japan: nishiura@bioinfo.osakafu-u.ac.jp

66 Engineering in Agriculture, Environment and Food Vol. 5, No. 2 (2012) planting season. In winter, use of this method is effective in Figure 3 shows the seeds sown in the stubble hole, which controlling water leaks, preventing overgrowth of weeds, has already been closed, such that birds cannot locate the improving land leveling, disposing of waste straws, and seeds. promoting tillering and root development. An inter-ditch distance of approximately 200 mm is ideal for obtaining the maximum number of seedlings and tillers per unit area (Hamada et al., 1995). Koide et al. (1997) reported that the rice yield obtained using this method is nearly the same as that obtained by custom transplanting. They reported that harmful competition between rice plants sometimes occurs due to dense plantation (Koide et al., 1997). To avoid the harmful effects of such dense plantation, large amounts of agricultural chemicals must be applied, resulting in decreasing cost-effectiveness and increasing environmental stress. Therefore, rather than strip seeding, spot seeding is preferred to provide adequate ventilation and decrease the harmful Fig. 2 Cross-sectional view of the area underneath the effects resulting from dense plantation. stubble. 2. Direct seeding beneath stubbles Figure 1 summarizes the proposed method of seeding directly beneath the previous year s stubbles. 1mm ① ② ③ ④ Fig. 1 Schematic diagrams of direct seeding beneath the previous year s stubbles. Fig. 3 Cross-sectional view of the region below the stubble This process consists of 4 steps: (1) aiming with a stick at after direct seeding. the planting position in the stubble, (2) boring a hole with the stick at the aimed position, (3) removing the stick, and (4) The described seeding method can overcome many of the seeding into the hole. Although soil hardness changes difficulties encountered in standard ditching methods, as according to field water content, the soil beneath the stubble follows. Seeding spots can be fixed depending on the stubble is consistently wet and soft regardless of the soil water position. Seeding spots prevent strip seeding, which content because the tillering portion is putrid at the time of sometimes occurs when using conventional seeding methods. seeding. Therefore, boring and seeding are relatively easier in This can cause overgrowth of rice and increase pest damage. stubble than in soils. Seeds are embedded into stubbles, solving the problem of bird Figure 2 shows a cross-sectional view of the area beneath damage that may sometimes occur due to insufficient the stubble. The blackish area in the figure, which is shaped covering of the seeds by soil, particularly in hard soil fields. like an inverted triangle, is the tillering portion of the rice that The porous and water-holding capacities of the tillering part was grown in the previous year, and is quite soft and porous of stubbles provide suitable conditions for rice germination with and seedling growth, which require a continuous water excellent aeration and water-holding capacity. Furthermore, the hole bored in the stubble gradually closes, providing the same effect as soil-covering. supply.

NISHIURA, WADA: Rice Cultivation by Direct Seeding into Untilled Dry Paddy Stubble -Proposal of a New Seeding Method and Germination Rate with That- 67 III Seeding Experiments 1. Objective Direct seeding into stubble was investigated in an experimental field at Osaka Prefecture University Farm under various conditions to verify the effectiveness of our new method, and also to devise a seeding method using a seeding implement that could easily sow rice seeds in stubbles. 2. Experimental conditions Figure 4 shows the position of seeding and fertilizing holes in stubbles. Three holes per stubble were bored for seeding, which were laterally aligned at intervals of mm with the center hole bored at the center of each stubble. We used 3 holes per stubble to reduce the overall mortality risk in stubble by transmission of disease and because it is common practice to transplant 3 seedlings in stubble by hand. Two holes per stubble were bored for fertilizing on the near side of the stubble. These holes were side-linear to the seeding holes at intervals of mm. The diameter of each hole was 10 mm. seeding until June 23 without irrigation control. Table 1 Seeding conditions in experimental plots (Seed number, Hole depth) Treatment Seed No. Depth [mm] Seed No. left hole center hole left hole T1 4 20 1 2 1 T2 4 1 2 1 T3 7 20 2 3 2 T4 7 2 3 2 3. Methods Figure 5 shows a seeding implement designed for the trials (Fig. 5, upper). Its manipulation procedures are shown in Fig. 5, lower. Seeding dates were May 22, 23, and 24, 2006. Experiments were repeated 3 times. Approximately 1 month after seeding (June 21, 2006), the germination number and stubble width were determined. Germination was confirmed by the development of above-ground sheath leaves. Stubble width was measured using a ruler in units of 5 mm. Front and behind Stubble Seeding holes Fertilizing holes Interval between each hole is mm Left and right Fig. 4 Position of seeding and fertilizing holes in the stubble. The depth of seeding holes was 20 mm or mm, and the depth of the fertilizing holes was 20 mm deeper than that of the seeding holes. Hinohikari, the rice cultivar used in the experiments, was provided by the Agricultural, Food and Environmental Sciences Research Center (Osaka Prefecture). Either 4 or 7 seeds were sown per stubble, corresponding to 2.5 kg/10 a or 4 kg/10 a. U-Coat 4 (MC Ferticom Co., Ltd) was used as a fertilizer. The amount of fertilizer used was 2.6 g per stubble, which is nearly equal to the amount used in the custom method and corresponds to kg/10 a (N content: 10 kg/10 a). Inter-row and intra-row distances between stubbles were 0 mm and 1 mm, respectively. Each plot area was 2 m 2 m and included 91 stubbles. Four experimental plots, hereafter referred to as T1 to T4, were prepared according to the seeding conditions (T1: 4 seeds, 20 mm depth; T2: 4 seeds, mm depth; T3: 7 seeds, 20 mm depth; T4: 7 seeds, mm depth; T5: furrow treatment; Table 1). Sowing in each experimental plot was repeated 3 times under the same experimental conditions; therefore, in all, 12 experiment plots were prepared. Water conditions depended on the frequency of rain and sunshine during the month after 1 2 3 4 1 Aiming with a stick at planting position in stubble in the combined form 2 Boring a hole at the position aimed at with the stick 3 Seeding and fertilizing in the hole after stick removal 4 Removal of seeding implement Fig. 5. Seeding implement designed for experiments (Upper left: Combined form; Upper right: Divided form; Lower: Manipulation steps for seeding). IV Results and Discussions

68 Engineering in Agriculture, Environment and Food Vol. 5, No. 2 (2012) 1. Germination rate at each seeding hole The germination rate, i.e., the ratio of the germination number to the number of seeds embedded in the hole, was calculated at each seeding hole. Figure 6 shows the germination rate estimated from the sum of results obtained in 3 repeated experiments, commencing on May 22, 23, and 24, 2006. (a) T1 a a a (b) T2 a b a (c) T3 a a a (d) T4 a b ab Fig. 6 Germination rate in seeding holes. The standard deviation of the 3 repeated experiments is shown as an error bar in the figure. The letters in the figure signify the significant differences with analysis of variance at the 5% significance level. In the T1 and T3 treatments (at a seeding depth of 20 mm), there was no significant difference in the germination rates between the center hole and the side holes. In contrast, in the T2 and T4 treatments (at a seeding depth of mm), the germination rate was lower in the center hole than in the side holes. The germination rates in side holes may be affected by the lateral diameter of stubble, because seeds in the side holes may be covered by stubbles with a large lateral diameter. Therefore, we next investigated the relationship between germination rate and lateral stubble diameter in each experimental plot on each experimental day. The total germination rate in the stubble is shown in Fig. 7. The standard deviation of the 3 repeated experiments is shown as an error bar in the figure. The letters in the figure signify the significant differences with analysis of variance at the 10% significance level. We used the 10% level of significance because we found no significant differences with analysis of variance at the 5% significance level. In the T2 and T4 treatments (at a seeding depth of mm), the germination rate was the same or higher than that in the T1 and T3 treatments (at a seeding depth of 20 mm). 75 65 55 45 Germination rate in stubble ab a b a T1 T2 T3 T4 Fig. 7 Total germination rate in stubble for each experimental condition. 2. Germination rate in side seeding holes and the lateral diameter of stubble Stubbles were sorted every 10 mm according to lateral diameter measured at 5 mm unit. For example, a diameter of between 47.5 and 52.4 mm indicated mm, and a diameter of between 52.5 and 57.4 mm indicated 55 mm; stubbles with diameters of mm and 55 mm were categorized as mm. Therefore, stubble with a diameter between 47.5 and 57.4 mm was categorized as stubble with a diameter of mm. Data were omitted when the number of stubbles with a diameter of less than mm or greater than mm was less than 5. Figure 8 shows the relationship between the germination rate in side seeding holes and the lateral diameter of stubble. The results of 3 repeated experiments, commenced on May 22, 23, and 24, 2006, are summarized. At a seeding depth of 20 mm (in treatments T1 and T3), there was a positive correlation between germination rate in side holes and the lateral diameter of stubble. At a seeding depth of mm (in treatments T2 and T4), the correlation was positive up to a diameter of mm but

NISHIURA, WADA: Rice Cultivation by Direct Seeding into Untilled Dry Paddy Stubble -Proposal of a New Seeding Method and Germination Rate with That- 69 became negative at diameters greater than mm. However, the correlation was less significant than that observed for a seeding depth of 20 mm. (a) T1 (b) T2 (c) T3 (d) T4 Fig. 8 Relationship between germination rate in side seeding holes and the lateral diameter of stubble The results indicate that, at a seeding depth of 20 mm, germination rate was higher in the center than in the marginal region of stubbles, whereas, at a seeding depth of mm, the germination rate was higher in the marginal region than in the center of stubbles. Since the distance between the left and right seeding holes was mm, side holes could be covered by stubble with a large lateral diameter, thereby providing better protection against bird damage. Therefore, at a seeding depth of 20 mm, an increase in stubble diameter may lead to an increased germination rate in side seeding holes. In contrast, at a seeding depth of mm, the germination rate in side seeding holes was slightly decreased with increasing stubble diameter of mm and higher. These results can be explained by the shielding effect of stubble on sunlight, which causes restriction of seedling growth when seeds are planted at a depth of mm. V Summary and Conclusions In this report, we propose direct seeding into the previous year s stubbles as a labor-saving rice cultivation method in untilled dry paddy fields. The effectiveness of this method was determined by seeding experiments. Three seeding holes at depths of 20 or mm were bored into stubbles. The center hole was bored at the center of the stubble, and 4 or 7 seeds were sown per stubble. Four sets of experiments were designed with different combinations of seeding depth and seeding number. Each experimental plot was 2 2 m, and contained 91 stubbles at intervals of 1 mm and inter-row distances of 0 mm. Each set of experimental conditions was replicated in 3 plots. Germination rate and stubble width were determined 1 month after seeding. Our study yielded the following findings. (1) The germination rate was high in the center of stubbles when the seeding depth was 20 mm and in side seeding holes when the seeding depth was mm. (2) By analyzing the relationship between germination rate in side seeding holes and lateral stubble diameter, we found that the germination rate was higher in stubbles with a larger lateral diameter when the seeding depth was 20 mm but decreased in stubbles with a lateral diameter greater than mm when the seeding depth was mm. These results suggest that seeding in stubbles may be effective in preventing bird damage typically noted with shallow seeding (20 mm depth) but restricts seedling growth with deep seeding ( mm depth) through the shielding of sunlight. References Hamada, Y. 1995. XII No-tilled direct seeding cultivation on a well drained paddy field puddled in winter. (In Japanese). The Outlines of Agricultural Technology 17(2):88 99. Kimoto, H., S. Okatake and Y. Tomihisa. 1995. Non-tilled direct seeding culture on well-drained paddy field-rice production for only 5 h per 10 a (First Edition) (In Japanese). Rural Culture Association, Tokyo, 99 100.

Engineering in Agriculture, Environment and Food Vol. 5, No. 2 (2012) Koide, T., M. Takamatu, K. Ito and T. Yoshida. 1997. The analysis of the growth characteristics of rice plants under No-till direct seeding culture on a well-drained paddy field (In Japanese). Research Bulletin of Aichi Agricultural Research Center 29:27 32. Okamura, S. 2001. Seed coating with calcium peroxide (In Japanese). The Outlines of Agricultural Technology, 23 (2-1):4 7. Okatake, S. 1998. Non-tilled rice culture on paddy field (In Japanese). The Agricultural Technology 53:8 11. Washio, M. 2003. Characteristics of direct seeding cultivation style (In Japanese). The Outlines of Agricultural Technology 25(344):2 5. (Received : 28. October. 2010, Accepted : 24. October. 2011)