Establishment rate of direct-seeded rice in the relay-intercropping system in Kanto region of Japan

Natsumi Okamura,Satoko Yasumoto,Makoto Kojima,Masaki Okamura,Yasuo Ohshita

doi:10.1080/1343943x.2018.1486215

Abstract

ABSTRACTThe relay intercropping system for cultivating direct-seeding rice and winter cereal is a low-cost method particularly for double cropping, because it eliminates the steps of raising seedlings, paddling, and transplanting. However, in this system, the seedling establishment rate (SER) of rice is low and unstable. The objective of this study was to identify the factors affecting SER to highlight the ways to improve SER. Experiments were conducted in experimental fields in Tsukuba City, Ibaraki Prefecture in 2015 and 2016. To determine the time of rice seed death and to calculate seed survival rates, ‘Akidawara’ seeds were embedded in soil (depth: 3 cm) and dug up after defined periods. We then analyzed the correlation between SER and meteorological factors at two sites (Ibaraki Prefecture and Gunma Prefecture) over the same two years. Based on mean air temperature (MT), we divided the period from seeding to June 20 (when irrigation had been initiated in almost all the fields) into four phases. In Phase 1, the number of days with rainfall (≥5 mm) and soil-wetting days (water potential ≥ −100 kPa) were significantly and negatively correlated with SER. We found that most of the seed deaths occurred after germination, and the germination rates were presumably affected by water absorption during the low temperature phase. Further investigations are needed to understand the occurrences during the seedling emergence period. This study contributes to a better understanding of the factors affecting variations in the SER of direct-seeded rice grown in the relay-intercropping system.List of Abbreviations: DSR: direct-seeded rice; SER: seedling establishment rate; TT: thiuram treatment; SSR: seed survival rate; DS: dead seeds; AGS: already germinated seeds; DSRI: direct-seeding of rice in the inter-row spaces of winter cereals; VWC: volume water content; WP: water potential

Highlights

In Japan, double cropping covers an area of approximately 83,000 ha (Ministry of Agriculture, Japan, 2015), of which 14,200 ha is within the Kanto region
We have previously reported (Maki, Hosobuchi, Kojima, Yasumoto, & Ohshita, 2016) that the yield of the direct-seeded rice grown in the inter-row spaces of winter cereals (DSRI) is possibly more stable than that of the Direct seeding of rice (DSR) grown after harvesting winter cereals, and that the yield of DSRI rice can be higher depending on the year
The present findings indicate that early sowing may affect seedling establishment rate (SER) negatively because of rainfall in Phase 1; treatment aimed at prevention of water absorption and selection of varieties that show enduring seed vigor even in the face of unsuitable temperature must be researched in future

Summary

Introduction

In Japan, double cropping covers an area of approximately 83,000 ha (Ministry of Agriculture, Japan, 2015), of which 14,200 ha is within the Kanto region. In the double-cropping areas, winter cereals are not harvested until early June, and rice is planted in the mid- or late June after tillage and irrigation of the field. In double-cropping systems, the workload (i.e. harvesting of winter cereals, tillage, plowing, and transplanting) in June is severe for large-scale farmers. Relay intercropping of direct-seeded rice and winter cereal might distribute the workload and resolve the problem by ensuring a longer growing period because of early seeding. In this system, rice seeds are directly seeded into the inter-rows of winter cereals (e.g. wheat or barley) in March or April.

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