2005 Volume 74 Issue 3 Pages 291-297
Soil nitrogen mineralization and nitrogen absorptions by rice in paddy-upland rotational fields (rice-wheat-soybean) were studied in the Nara basin for four years (2000-2003) in comparison with those in adjacent single-cropped paddy fields. Under conditions of no nitrogen fertilization, the crop rotational fields did not increase soil nitrogen mineralization owing to decrease of total nitrogen and carbon in the soils by repeated crop rotations. However, rice at the heading and maturity stages had higher nitrogen absorptivity and higher nitrogen content in the rotational fields than in the single-cropped paddy fields, resulting in a larger number of spikelets per panicle and higher yield in the crop-rotational fields. Soil nitrogen mineralization of a paddy-upland rotational field did not vary with the year, but largely varied with the field due to physicochemical properties of their soils. The difference in the soil properties between single cropped and crop rotational fields may be minimized by supplying a nitrogen source such as organic manure to the latter.
