Seed Source Effects on Germination, Growth, and Yield of Carrots Under Natural Farming

Natural farming (“Shizen-noho” or “Shizen-no” in Japanese) is a type of organic farming that is widely perceived in Japan to be a method of sustainable cultivation. Since the development of theories and methodologies in the 1930–1940s, natural farming has spread not only in Japan but also throughout the world (Fukuoka 2004; Sawanobori & Komatsuzaki 2019). The most distinguishing feature of natural farming from organic farming is that it does not use any materials derived from animals, including manure (Sawanobori & Komatsuzaki 2019). Some of the natural farming groups do not even till or weed to avoid disturbing the soil surface. These methods often result in lower yields; the amount of soil nutrients readily available to plants is generally lower than other farming methods, and weeds compete with crop growth. Despite the disadvantage of low yield, natural farming continues to attract many people (Kawaguchi et al. 2014; Mitra et al. 2017). This is because natural farming is considered to be more compatible with nature and more sustainable than organic farming (Fukuda 2018).

Since no survey has been conducted on the current status of natural farming, it is not possible to provide figures on the area under natural farming cultivation or the number of natural farming practitioners. However, the following data provided by Japan’s Ministry of Agriculture, Forestry, and Fisheries (MAFF 2017) may help in understanding the current state of agriculture in Japan. The number of agricultural management entities was approximately 1.38 million in 2015, of which 1.34 million were family-owned entities, accounting for 98% of the total agricultural management entities. Of these agricultural management entities, 52.8% operate less than 1 ha and 91.2% less than 5 ha (Fukasawa 2020). The area of Japanese Agricultural Standard – JAS-certified organic farming – was only 0.5% of the total agricultural land in Japan in 2017 (Sawanobori & Komatsuzaki 2019). Due to the high cost of obtaining JAS organic certification, in fact, the percentage of farmland without JAS certification has increased by about 19% from 2009 to 2017 (MAFF 2019), and the number of organic farmers without JAS certification is about double that of certified organic farmers (Sawanobori & Komatsuzaki 2019).

For a long time, Japan relied on imports of chemical fertilizers, agricultural chemicals, and even organic fertilizers. These materials can be used at a low cost in the short term, but in the long run, there is a risk of increased costs, both economically and environmentally. Researching and practicing natural farming methods from a long-term perspective will be effective as one way to guarantee sustainable production of agricultural products in the future. In natural farming, many changes observed are long-term, occurring slowly over time (Takahashi 2010). Production of on-farm seeds adapting to a natural farming environment across generations has been positioned as one of the important technologies in natural farming (Sawanobori & Komatsuzaki 2019). Phenotypic plasticity through epigenetic mechanisms may be an important contributor to the adaptation of plant species to different environments (Bräutigam et al. 2013; Balao et al. 2018). Studies have indicated that the ancestral environmental conditions of plants can influence the progeny phenotype through epigenetic mechanisms (Boyko & Kovalchuk 2008). Therefore, producing self-produced seeds across generations may potentially promote seed germination, growth, and yield of vegetables under natural farming conditions.

Although hybrid seeds often have higher yields compared to open-pollinated seeds (Kutka 2011), they can perform well only under high-input agricultural management (Macharia et al. 2010; Omondi et al. 2014). Conversely, open-pollinated seeds can be produced by farmers. This means that self-produced seeds adapted to local soil conditions can potentially result in higher crop yields compared to hybrid seeds. However, to the best of the authors’ knowledge, there have been no scientific studies that investigated and compared the performance of self-produced seeds under natural farming to other types of seeds. This paper reports the findings of a field experiment investigating the crop performance from different seed sources under natural farming conditions. A root vegetable was selected because the root-to-shoot (R : S) ratio has been shown to be altered by the nutritional conditions of the maternal plant (Verhoeven & van Gurp 2012). Open-pollinated seeds of carrots (Daucus carota L.) produced on the farm under natural farming were compared with seeds of the same cultivar produced under conventional farming and with seeds of a hybrid cultivar used commonly in conventional farming. The germination rate, growth, and yield of carrots from each type of seed were studied under four different cultivation methods, including two different natural farming methods.

Self-produced seeds showed positive effects under natural farming conditions in improving crop performance compared to other seeds. In autumn 2017, the germination rate of OPN seeds was higher than that of other seeds under the NF2 regime. NF2 did not involve tillage, so the soil temperature was likely lower than that with other methods using till-age. The temperature of the soil, when covered with grass mulch without plowing, can be up to 5 °C lower than that under conventional farming (Jelonkiewicz & Borowy 2009). As OPN was self-produced under the natural farming system method, the supply of nutrients in the maternal environment was generally low. Luzuriaga et al. (2006) showed that when the maternal environment was nutrient-rich, the germination rate was slow. Although further tests are required to verify our findings, nutrient conditions may have affected the seed germination rate, making the OPN seeds germinate well even at lower temperatures. The higher germination of OPN compared to HB and OPC seeds in spring 2018 was also in line with this phenomenon. The average temperature during the germination period in spring 2018 was 8.5 °C, which was below the optimum temperature (15–25 °C) for carrot germination (Corbineau et al. 1994; Rubatzky et al. 1999). The higher germination rate at low temperatures may result in a longer growth period, which is often necessary to obtain sufficient yield under natural farming (Takahashi 2010).

Similar to the results of germination rate, the results for root fresh weight also indicated the potential superiority of self-produced seeds. In autumn 2017, root fresh weight and other root parameters of OPC were significantly lower than for HB seeds, as expected, since hybrid seeds generally have higher yield than open-pollinated seeds due to heterosis (Golmirzaie et al. 1998). On the other hand, the root parameters for OPN were as high as for HB seeds, suggesting that the self-produced seeds may enable farmers to obtain open-pollinated seeds that have a yield potential similar to that of hybrid seeds. However, in spring and autumn 2018, no such differences were found, and the values for OPN were actually the lowest among the three seed sources. This discrepancy among different cultivation seasons could be due to the difference in years invested in seed self-production. The seed type used for OPN in autumn 2017 was ‘Kuroda-gosun’, which had been self-produced for more than 10 generations. On the other hand, the seed type used in spring and autumn 2018 was ‘Chikumano-gosun’, which had been self-produced for only two generations. The possibility of different genotype responses to natural growing conditions should also be taken into account. In contrast to the previous study that showed changes in the R : S ratio with the maternal nutrient conditions (Verhoeven & van Gurp 2012), no R : S differences between OPN and OPC seeds were detected, and the only difference detected was between HB seeds and others. Since the difference in R : S ratio among the contrasting cultivars is similar across the environmental gradient (Xu et al. 2018), the difference between cultivars in our study may have masked any responses to the maternal environment for R : S in open-pollinated seeds. It was difficult to detect the difference between means on seed sources compared to cultivation methods because the alpha levels are adjusted for the multiple comparisons. Furthermore, the R : S ratio under NF2 was lower than that under CT and NF1 in this study, probably due to the increased soil strength under notillage, which in turn inhibits root growth (Howeler et al. 1993).

Compared to other cultivation methods, the yield of NF2 was much lower. This is not surprising, considering that this is only the result of the first or second year. One of the well-known leaders of this farming method stated that it took 10 years to get a reasonable yield because it takes time for the soil to become suitable (Kawaguchi & Tsuji 2011). In Japan, the main soils, called andosols, can fix large amounts of organic matter (Sawanobori & Komatsuzaki 2019). In the field experiments conducted in Japanese soils, soil organic carbon has been shown to increase when cover crop residues and weed residues are combined with no-till systems (Arai et al. 2014; Higashi et al. 2014). A meta-analysis of the relationship between soil carbon and crop yield has shown that crop yield increases with increasing carbon concentration (Oldfield et al. 2019). In addition to increasing carbon concentration, no-till systems also contribute to the diversity of soil microbiology and animal communities (Komatsuzaki & Ohta 2007; Kaneko et al. 2018; Sawanobori & Komatsuzaki 2019). Filser et al. (2016) found that soil microbiological and animal activity has direct and indirect effects on carbon sequestration and nutrient supply. No-till cultivation represented relatively lower yields in the first 1–2 years, but after 4–5 years the yields were comparable, and after 6 years the yields were higher in no-till cultivation (Pittelkow et al. 2015). Hence, it is expected that in NF2, crop yields will gradually increase with increasing carbon concentration over time, although yields will decrease initially.

Natural farming is not an established field of research, but it is the one that should be expanded in the future. In fact, to the best of our knowledge, there are no previous studies similar to the present study at this time. A long-term trial with NF2 may reveal the effects of seed self-production.

In this study, the germination rate of self-produced seeds was higher than that of other seeds. In addition, the root fresh weight and other root parameters of self-produced seeds for more than 10 generations were as high as for hybrid seeds. This suggests that using self-produced seeds by farmers improves crop performance in a natural farming system. Our research results also provided the implication that not only does soil preparation take years, but also seed self-cultivation may be effective only after years of repeated practice. It is necessary to develop technology to shorten the time it takes to secure the yield in a natural farming system.