Abstract
This study aimed to compare the causality of climatic factors affecting the yield of Italian ryegrass (IRG) between upland fields and paddy fields, by multi-group structure equation modeling. The raw data (n = 728) on forage contains both yield, field type, and the plantation address were collected from the Rural Development Administration, Republic of Korea. The climatic factors were: growing days, temperature and precipitation-in autumn and next spring seasons-from the climate big data of the weather information system of Korean Meteorology Administration. In the result, the composition of climatic factors was similar, but the causality by the paths was different between upland fields and paddy fields. In particular, yield in the paddy fields was sensitive to autumn precipitation because of short growing days in the rice-rotation system. In the paddy fields, the precipitation effect in both autumn and the next spring indirectly affected the yield through temperature. The autumn temperature effect on yield in the paddy fields was 2.82 times greater than in the upland fields, between the two field types, the spring temperature effect was somewhat similar after wintering; thus, IRG cultivation in paddy fields should be limited to the south. However, there is greater suitability for IRG in the upland fields in the autumn, where the benefits of higher temperatures accumulate to offset effectively the short growing days. This study will assist in checking areas suitable for IRG cultivation as a winter forage crop in the Republic of Korea. In the future, the structure established in this study will be expanded by adding variables related to soil physical properties from soil information system and cultivation management from survey sheets.
Highlights
Italian ryegrass (Lolium multiflorum Lam., IRG) is the most important winter forage crop because of its high feed value for livestock [1,2], and its cultivation in rice-paddy fields has been carried out tentatively in East Asia [3]
The yields were greater in the upland field than in the paddy field, while the dry-matter rate was greater in the paddy field (20.6%) than in the upland field (18.7%), which means that the paddy fields contained more soil moisture contents than the upland fields
It is likely that the soil moisture content was still high while cultivating winter crops, even if the water was drained after the rice harvesting since the paddy fields hold water for four to six months in the Republic of Korea
Summary
Italian ryegrass (Lolium multiflorum Lam., IRG) is the most important winter forage crop because of its high feed value for livestock [1,2], and its cultivation in rice-paddy fields has been carried out tentatively in East Asia [3]. Given the high dependency on foreign imports and an increase in feed prices, IRG cultivation is actively carried out in both paddy fields and upland fields of the Republic of Korea [6]. The difference is related to summer crop selection, mainly maize in upland fields and rice in paddy fields. These factors all cause a different growing period of winter forage crops because the harvest time of summer forage crops determines the seeding time of winter forage crops. We hypothesized that the relationship between IRG yield and climatic factors would differ based on the different growing periods of upland fields and paddy fields
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