1. Miyagi Prefecture
In Miyagi Prefecture, the agriculture-related damage (except livestock industry) due to the tsunami amounted to 545 billion yen, the disaster area was 14,300 ha, and most of this was fields and horticultural facilities. Recently, 92% of the damage has been repaired from the early severe stages of damage. Such recovery processes are described; for example, the case of Sendai City (City of Sendai, 2015). On the other hand, our research project also focuses on the new development stage after recovering the previous status. Four cities and towns located on the southern coast in the Sendai plain; Natori, Iwanuma, Watari and Yamamoto were selected as field trial and demonstration sites, which were characterized by typical paddy field management or protected horticultural crops, especially strawberries. Cultivation of field vegetables had not been so active in these areas, but it was regarded as useful for high profitability and maintaining employment in the off-season of rice culture. In the agricultural reconstruction plan of these areas, dispersed small paddy fields were combined into a 2 ha-wide field, and especially in Watari and Yamamoto, high strawberry tunnels and a grower’s residence located along the coast that was severely damaged by the tsunami resulted in migration to an inland area and subsequent development of wide upland fields in the remaining sites. The introduction of field vegetables to such a newly developed farm management allotype is an important target of this research project. This project “Field vegetables” was conducted and integrated by the Tohoku Agricultural Research Center, NARO, from 2012 to 2017, with members of the Miyagi Prefectural Institute of Agriculture and Horticulture, Central Region Agricultural Research Center (NARO), Institute of Vegetable and Floricultural Science (NARO), Akita Prefectural Agricultural Experimental Station and Yanmar Co. Ltd. These members supported the following 8 activities with the cooperation of Miyagi Prefecture Agriculture Department and Watari Agricultural Extension Center.
- • Introduction of forced asparagus culture
- • Mid-winter production of cabbage for processing
- • Spinach for processing
- • Integrated mechanization of cabbage and onion cultivation
- • Subirrigation system for upland field vegetables (OPSIS)
- • Integrated pest management using living wheat mulch
- • Growth prediction system for coordinated supply among separate production sites
- • Effective utilization of rice nursery greenhouses
Here, integrated mechanization of cabbage and onion cultivation, the main theme of our project, is mainly reviewed and discussed.
1) An integrated mechanical cultivation system for cabbage
One of the projects was designed to incorporate cabbage cultivation as a profitable product in large-scale farm management, especially for paddy field areas following the 2011 Tsunami Disaster. In the project, an integrated mechanical cultivation system that can perform every operation using agricultural machines was applied to avoid labor competition practices between paddy rice, wheat or soybeans with cabbages. A field trial was conducted in a community-based farming system in Iwanuma city, which is located on 2 km from the coast and has a large-scale paddy and upland field that was affected by the Tsunami Disaster. In this section, an outline of the project is firstly shown and several studies or techniques to address some system problems are explained.
2) Outline of the mechanical cabbage cultivation system
Cabbage (Brassica oleracea var. capitata) is an important vegetable in Japan. Due to the recent increase in demand for the processed cabbage (Kobayashi, 2018), its cultivation area has increased. Most areas have attempted to introduce an integrated mechanical cultivation system to avoid labor-intensive operations, especially for cabbage harvesting. The system has become feasible following recent commercial supply of cabbage harvesters in Japan (Fig. 1). In our project field trial, the first commercially-released cabbage harvester was introduced, and the applicability of the integrated mechanical cabbage cultivation system was compared to large-scale rice paddy-dominated farm management.
In our project, two seasons of cabbage cultivation were introduced (early summer and autumn-winter) without intense labor competition with paddy rice or soybean cultivation (Table 1). In the early summer-harvesting cropping type, cabbage seeding was conducted in March and ridging with fertilization and transplanting followed in April, which is the period before the rice-planting season. After the rice-planting period, cabbage can be harvested from late June to July. For the autumn to winter-harvesting type, cabbage seeding and transplanting was conducted before the rice-harvest season, and harvest was carried out from October to February, the off-season for rice and soybean cultivation.
One of the advantages of managing cabbage cultivation could be labor sharing with rice and soybean cultivation, which are usually the main sources of income, as well as the year-round agricultural operations. In addition, mechanized cabbage cultivation is easily acceptable to farmers in the paddy rice-dominated management, where almost every practice for the paddy rice and soybean cultivation can be mechanically operated, and which can be attractive especially for senior farmers because of the relatively low labor-intensity.
However, this system has some problems. Because it requires a substantial initial investment to introduce an integrated mechanical system, it is necessary to use a relatively large-scale cultivation area (more than 10 ha) for cabbages, or to obtain some financial support. Another problem involves stable production with continuous shipping of uniform standard products, which has become difficult recently due to extreme weather events such as regional droughts and heavy rain. Cabbage cultivation skills are also necessary because its cultivation season can be potentially limited and needs to shift from the most suitable growing season due to labor competition with rice or soybean cultivation.
3) Studies and techniques for the mechanical cabbage cultivation system
Our project dealt with some of the above problems and proposed several countermeasures as follows.
(1) Fertilization of the cabbage for processing at the trial site
In the field trial site, named ‘Hayashi Rice’ (sandy loam soil) in Iwanuma City, leaching of fertilizer became a problem, especially in the autumn-winter-harvesting type. In addition, the standard weight of the cabbage intended to be eaten raw (around 1 kg) is substantially different from that of the cabbage for processing such as cutting or cooking (around 2 kg or more). However, the fertilizer application volume for the two cabbage types was easily confused because few studies dealt with the fertilizer application volume of the latter cabbage. To determine this, the volume of nitrogen uptake per strain is more important than the volume per area because the planting density is different according to the cultivar, cultivation season, and/or sale destination. The recommended level for processed cabbage, calculated based on our studies, could be much higher than that for unprocessed cabbage (25 kg N/10a, standard for Miyagi Prefecture). Based on this, the fertilization at the trial site was improved by increasing the total application volume and by allocating a greater volume to the later growth stage.
In our project, a partial mixing and application technique for fertilizer in the ridge, using a tractor-attached agricultural machine that can do ridging and partial fertilization simultaneously, was introduced (Fig. 1, “ridging with fertilization” and Fig. 2). This machine was developed by NARO Tohoku Agricultural Research Center and NARO Central Region Agricultural Research Center (Yashiro, 2006). Its abilities to reduce fertilizer-application volume and to contribute to uniform production have been examined mainly by the NARO Central Region Agricultural Research Center. Using this machine, two operations (ridging and fertilization) can be conducted at once, which can contribute to time- and labor-saving. Moreover, the fertilizer application by the machine is limited to the middle zone of the ridge, which is comparable to the root zone of the seedlings. This can lead the effective nutrition uptake and thus could contribute to a reduction in the fertilizer application volume.
Figure 3 shows seedlings grown under a nursery bed for a longer period (40 days or more) than the normal period (around 30 days) without applying additional fertilizer. These seedlings show retarded growth and seem senescent, but can keep their vitality for a prolonged period or can be tolerant to a dry soil after transplanting (Sato et al., 2003). A delay in transplanting, or unsuitable conditions just after transplanting could potentially happen at the trial site because of the labor competition with paddy rice or soybean production. Research into these issues was provided by Miyagi Prefectural Institute of Agriculture and Horticulture, and they mentioned that the survival rate, harvesting period and the yield of the long-term grown seedlings were not different from the normal-grown plug seedlings (Sawasato, 2015b).
(3) Deeper planting of plug-grown cabbage seedlings to mitigate lodging
Cabbage harvesting is the most labor-intensive operation because of the heavy weight, but it can be conducted in a labor-saving way using machine harvesting. In 2013, a cabbage harvester was firstly released from Yanmar Co. Ltd. and it has already become widespread in Japan (Fig. 4). However, cabbage lodging (Fig. 5) is one of the problem that can potentially reduce the performance of the cabbage harvester (Fukushima and Sato, 2009; Yoshiaki et al., 2008). We proposed a countermeasure technique in which a plug-grown cabbage seedling was transplanted to a deeper soil depth, which could mitigate the lodging in the harvesting period (Figs. 6 and 7; Yamamoto et al., 2015). This is partially due to the improvement in root anchorage as cabbage developed a larger number of thin roots in a slightly deeper soil depth, resulting in a higher lodging resistance to the lateral pushing (Fig. 8; Yamamoto et al., 2016). Transplanting the seedlings to a deeper soil layer can be easily conducted using a cabbage transplanter by setting the depth lever to a deeper position. This has potential to improve cabbage lodging furthermore along with combining with other techniques such as breeding.
The initial growth stage is the most important period in the autumn-winter cultivation type. However, the growth is easily affected by dry period or heavy rain caused by typhoons or other abrupt changes in the weather at our trial site, located in a coastal area of Miyagi Prefecture. Thus, we applied several countermeasure techniques against both weather conditions (Fig. 9). Open-channel drainage and mole drains were used to facilitate runoff and subsurface drainage, respectively. On the other hand, irrigation in excessive dry periods was performed using a self-propelled irrigation sprinkler or irrigation tube. At the trial site, both techniques could contribute to a stable initial growth for cabbage even with very dry conditions or local heavy rain experienced in recent years.
(5) Demonstration of the culture system
A demonstration event of the mechanized culture system was held once a year for farmers, local government advisors, researchers and vegetable processing facilities (Fig. 10).
(6) Future issues
Finally, major remaining problems on our project are briefly discussed below.
It is still difficult to achieve stable production that can enable shipping of a fixed amount of processed cabbage continuously. It may be easier for the community to set up operations for cabbage production in the off-season for paddy rice or soybean production in winter. However, cabbage cultivation from summer to winter is not easy because growth is delayed as the weather gets colder. Besides, the management of continuous shipment that can simultaneously grow several cultivars or a single cultivar with different planting dates can become complicated. Therefore, it is important to carefully consider the cultivar (or a combination), transplanting period, production area, and other cultivation methods.
Farmers in paddy rice-dominated large-scale management are likely to be unfamiliar with vegetable production. Therefore, it is necessary to develop an easy and simple cultivation method with technology contributing to stable cabbage production, as well as a continuous support to acquire the necessary skills.
On these points, at least, several horticultural studies with a view to taking a leading role in the long-term reconstruction process are needed.
4) Field trials other than cabbage mechanization
i) Forced culture of asparagus: very effective for seasonal labor balancing for rice and soybean-dominant large-scale farmers because forced asparagus is harvested from January to March, the off-season for rice and soybean-dominant farmers (Matsuo et al., 2013). Field trials were done in ‘Koya Agri-Service’, Natori City, but the drainage from fields did not work well, growth of asparagus rootstock was retarded, and finally young spear yield did not reach an acceptable level.
ii) Mid-winter production of cabbage for processing: mulching with black plastic films allowed production in mid-winter, the usual off-season, at a trial site of Koya Agri-Service (Sawasato, 2015a).
iii) Spinach for processing: sowing time and variety choice was tested in a trial field of ‘Hayashi Rice’ and an elite variety was selected.
iv) Onion mid-scale integrated mechanization system: Achieving climatic advantages in a coastal area in a cold region, two-season onion growing (autumn and spring sowing) was possible with mechanization for mid-scale growers (Sawasato and Ohmori, 2016; Yamasaki, 2017). Water demand for spring sown onions was also studied to clarify the optimum irrigation timing (Yamamoto et al., 2017a, b, 2018). Field trials were applied at both Koya Agri-Service and Hayashi Rice.
v) Subsurface irrigation system for upland field vegetables (OPSIS): A new subsurface irrigation system was evaluated as an effective technology not only in a year with lower precipitation than usual years, but also in a year with usual precipitation (Sasaki, 2018; Sasaki et al., 2013, 2014, 2017). Using the data obtained from these evaluations, a field trial on their increased effect of OPSIS irrigation on spinach culture was applied at Watanabe Farm, Yamamoto Town, and subsurface irrigation by OPSIS proved to increase spinach yield more than conventional top irrigation.
vi) Integrated pest management using living barley mulch: In onion and cabbage cultivation, barley living mulch reduced the damage by thrips and hornworms with a combination of pheromone and yellow light traps. Field trials were done at applied in Koya Agri-Service.
vii) Growth prediction system for coordinated supply among separate production sites.
viii) Effective utilization of rice nursery greenhouses, especially for temperature reduction facilities in greenhouses in midsummer. The choice of material used in clothes and fine-mist cooling of greenhouses were effective ways to lower the body temperature (Koike et al., 2017).
2. Nursery trials in Fukushima Prefecture
The damage from the Tsunami 2011 in a coastal area was very severe in Fukushima Prefecture, and damaged farmland amounted to 4,571 ha. Moreover, the accident at Tokyo Electric Power Company Fukushima Daiichi Nuclear Power Station caused not only contamination of farmlands and associated products (Yamaguchi et al., 2016), but also delayed the restart of farming by long-term avoidance of polluted areas. Accordingly, Fukushima Prefecture Government rapidly started a radioactive materials measurement team (Fukushima Prefectural Government, 2016) and Fukushima Prefecture Government, NARO and other institutions and universities around the country worked on the development of countermeasure technology for radioactive pollution (Shinano, 2016).
Certainly, the radiocesium contamination levels of agricultural products just after the accident were higher because of the direct deposition of radionuclides on the surface of plants. Later, radiocesium contaminations in vegetable crops rapidly decreased and radiocesium in most annual vegetables planted after June 2011 has not been detected (Kobayashi et al., 2014). The reason is because exchangeable potassium in soil tends to be maintained at a relatively high level in vegetable fields, and potassium fertilization decreases Cs uptake and transfer from the soil to plants (Kubo et al., 2017; Shinano, 2016).
Because in this research project field trials at production sites were necessary, the subject of this research should be limited to vegetable nurseries to avoid the adverse impact of radioactive pollution. In this article, among the research trials of vegetable nurseries, studies on broccoli plug seedlings established by a bottom watering system with application of NaCl solution were introduced to increase the drought-resistance of seedlings.
1) Background of the trials
In Hama-dori, a coastal area in Fukushima Prefecture, autumn and winter-harvest broccoli was one of the major field vegetables before the disaster. The re-establishment of stable production of broccoli should be a touchstone for the restoration of agriculture in Hama-dori. Since the nursery season is only mid-summer (July and August), the main problems were labor-saving of daily watering and the addition of stress resistance, especially for drought, after transplanting in order to maintain the quality of plug seedlings. To solve these problems, a combination of a bottom watering system and irrigation with NaCl solution was tested.
2) Outline of the results
The developed bottom watering system is shown in Figure 11. Setting a special mat for bottom watering in a pool, plug trays are sub-irrigated by irrigation tube. Watering is timer-controlled and stagnant water is drained from a lapped mat outside the pool. This system consists of low-cost materials. Irrigation with NaCl solution (0.3% (w/v) instead of tap water is applied for approximately one week before transplanting to fields (Tokiwa, 2008).
Irrigation with NaCl solution did not affect the growth parameters of broccoli ‘Ohayo’ plug seedlings, including leaf color (Table 2). After the irrigation ceased, irrigation with NaCl solution also retarded the wilting of plug seedlings for approximately 4 days (Figs. 12 and 13). Accordingly, irrigation with NaCl solution instead of tap water increased the drought resistance of broccoli plug seedlings. Such additional environmental resistance will be very valuable for rooting at transplantation and increasing uniformity of the subsequent growth because broccoli seedlings are transplanted only in mid-summer, when seedlings may endure a severe climate, for example little rain, strong sunlight, and typhoons. The combination with a bottom watering system made this NaCl irrigation technique highly labor-saving.
3) Nursery trials other than broccoli plug seedlings
Mass-production of onion plug seedlings by sub-irrigation was also investigated and proved very useful for the promotion of Hama-dori field vegetables. Growth uniformity by sub-irrigation, insect pest control of strawberry nursery plants with high concentration CO2 air, powdery mildew control of strawberry plants by UV-B lighting, and omission of additional fertilizer by whole base application within the broccoli plugs were investigated in several trial fields in Fukushima Prefecture.
3. Iwate Prefecture—open field cucumbers
In Iwate Prefecture, the agriculture-related damage due to the tsunami was estimated at 68.8 billion yen, and the disaster area was 725 ha. The coastal area of Iwate is very narrow and the level places suitable for large-scale agriculture are very limited as a mountain range comes very close to the sea. Accordingly, the agricultural damage level was relatively lower than Miyagi and Fukushima, but the impact was still great and similar to the other two prefectures. Labor-intensive agriculture, for example, small-scale protected horticulture and fruit trees, was common in the Iwate coastal area and, in this project, the open field culture of cucumbers, one of the main crops of this area, was chosen.
Open field cucumbers are transplanted to fields in late spring and continue to grow until autumn. This does not need large-scale facilities and is characterized by high profitability, but the key point that influences the profitability is to maintain the plant vigor as long as possible, leading to a long harvest period and high yields. On the other hand, in most of the tsunami disaster area, the surface soil was often peeled to avoid salt pollution of the field, so plowed soil is shallow and it seems difficult to maintain the plant vigor over the hot season. Therefore, the fertigation (fertilizer-simultaneous irrigation) technique was introduced to the trial site in Rikuzentakata City to extend the harvest period of open field cucumbers by maintaining a vigorous status.
1) Fertigation technique for open-field cucumbers
The fertigation technique involves a plastic tube for drop irrigation, a liquid fertilizer mixer with a Venturi-pump aspirator, and a mulching sheet. The nitrogen concentration in liquid fertilizer was estimated by the leaf number increase per 2 weeks using the following equation:
[nitrogen amount (g·m−2 per 2 weeks) = increase in leaf number (m−2 per 2 weeks)×0.0441+2.189]
2) Outline of the field trials
In the fertigation plot, the yield was increased by 27 or 93% compared with the conventional solid fertilizer plot; in the solid fertilizer plot, the plant vigor was retarded from August and also the yield was decreased while in the fertigation plot, the vigor was maintained after September onwards and the yield in autumn was markedly increased compared with the conventional plot (Fig. 14). The amount of nitrogen application in conventional solid fertilizer (40 kg per 10 a) was decreased to 22.9 kg per 10 a by the fertigation technique. These techniques were manualized and widespread use is expected.
