Status of paddy soils as affected by paddy rice and upland soybean rotation in northeast Japan,with special reference to nitrogen fertility |
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| Authors: | Mizuhiko Nishida Hiroyuki Sekiya Koji Yoshida |
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| Institution: | 1. NARO Tohoku Agricultural Research Center , Shimofurumichi 3, Yotsuya, Daisen , Akita 014-0102 , Japan mizuhiko@affrc.go.jp;3. NARO Tohoku Agricultural Research Center , Akahira 4, Shimokuriyagawa, Morioka , Iwate , Japan;4. NARO Tohoku Agricultural Research Center , Shimofurumichi 3, Yotsuya, Daisen , Akita 014-0102 , Japan |
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| Abstract: | To investigate the current available nitrogen (N) and chemical properties of paddy soils affected by crop rotation between irrigated paddy rice (Oryza sativa L.) and upland soybean Glycine max (L.) Merr.] (paddy-upland rotation), topsoils were collected from 22 fields of four different farmers in the northeastern region of Japan. Regardless of organic material application, a significant negative correlation was found between available soil N and an increase in the proportions of upland seasons to total crop seasons after the initiation of paddy-upland rotation. Soil total N and total carbon (C) also tended to decrease with an increase in upland frequency. In fields with repeated applications of cattle manure compost, the soil available N was higher than in fields where only crop residue was applied. A significant negative correlation was also found between the soil available N:total N ratio and upland frequency. This indicates that the part of soil N related to available N was notably lost by the use of paddy fields as upland fields. In order to sustain available soil N over the minimum suitable level of 80?mg?kg?1, upland frequency should not exceed 65% when only crop residues and no other organic materials are applied. The upland frequency can be raised by the repeated application of organic materials which maintain a higher level of available soil N. The results imply that care should be taken to maintain the N fertility of paddy soil at a suitable level in paddy-upland rotation, and that upland frequency and organic materials applied are important factors to do this. |
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| Keywords: | available nitrogen paddy soil paddy-upland rotation rice soybean |
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