ISSN:
1573-5036
Keywords:
intercropping
;
N2 fixation
;
natural15N abundance
;
ureides
;
Vigna umbellata
;
Zea mays
Source:
Springer Online Journal Archives 1860-2000
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Abstract The yield of N in maize (Zea mays L.) and ricebean (Vigna umbellata [Thumb.] Ohwi and Ohashi) were compared on a Tropoqualf soil in North Thailand in 1984 and 1985. Both species were grown in field plots in monoculture or as intercrops at a constant planting density equivalent to 8 maize or 16 ricebean plants per m2. The contribution of symbiotic N2 fixation to ricebean growth was estimated from measurements of the natural abundance of15N (δ15N) in shoot nitrogen and from analysis of ureides in xylem sap vacuumextracted from detached stems. The natural abundance of15N in the intercropped ricebean was found to be considerably less than that in monoculture in both growing seasons. Using maize and a weed (Ageratum conyzoides L.) as non-fixing15N reference plants the proportions (P 15N) of ricebean shoot N derived from N2 fixation ranged from 0.27 to 0.36 in monoculture ricebean up to 0.86 when grown in a 75% maize: 25% ricebean intercrop. When glasshouse-derived calibration curves were used to calculate plant proportional N2 fixation (Pur) from the relative ureide contents of field collected xylem exudates, the contribution of N2 fixation to ricebean N yields throughout the 1985 growing season were greater in intercrop than in monocrop even at the lowest maize:legume ratio (25∶75). Seasonal patterns of sap ureide abundance indicated that N2 fixation was greatest at the time of ricebean podset. The averagePur andP 15N in ricebean during the first 90 days of growth showed identical rankings of monocrop and intercrop treatments in terms of N2 fixation, although the two sets ofP values were different. Nonetheless, seasonal estimates of N2 fixation during the entire 147 days of legume growth determined from ureide analyses indicated that equivalent amounts of N could be fixed by ricebean in a 75∶25 intercrop and in monoculture despite the former being planted at one-quarter the density.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02370107
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