Measurement of N2 fixation in maize (Zea mays L.)—ricebean (Vigna umbellata [Thunb.] Ohwi and Ohashi) intercrops

Abstract

The yield of N in maize (Zea mays L.) and ricebean (Vigna umbellata [Thunb.] 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 m 2. The contribution of symbiotic N 2 fixation to ricebean growth was estimated from measurements of the natural abundance of ~SN (6~N) in shoot nitrogen and from analysis of ureides in xylem sap vacuumextracted from detached stems.The natural abundance of ~SN 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-fixing ~SN reference plants the proportions (P ~SN) of ricebean shoot N derived from N 2 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 ofN 2 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 average Pur and P~SN in ricebean during the first 90 days of growth showed identical rankings of monocrop and intercrop treatments in terms of N z fixation, although the two sets of P values were different. Nonetheless, seasonal estimates of N 2 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.Abbreviations. P = proportion of ricebean N derived from symbiotic N2 fixation; P~SN as calculated from ~SN abundance in total N of shoots; Pur as calculated from the relative abundance of ureide N in xylem sap.

A study on the improvement iron nutrition of peanut intercropping with maize on nitrogen fixation at early stages of growth of peanut on a calcareous soil

“…In addition, where soil (one being a legume) N fettility is high, legumes in the field thrive without fixing atmospheric N 2 , so high levels of soil nitrate can be a potent inhibitor of N 2 fixation (Streeter 1988). In intercropping systems, competition for soil mineral N between legumes and cereals can result in stimulation of biological N 2 fixation and increased harvest of total interplanted crops (Rerkasem et al 1988;Chandel et al 1989;Peoples et al 1995;Elabbadi et al 1996). Both the competition of N from intercropping maize and the improvement of Fe nutrition of peanut could promote N 2 fixation of peanut in this intercropping system.…”

Nodulation, Nitrogen Yield and Fixation by Bambara Groundnut (Vigna Subterranea (L.)Verdc.) Landraces Intercropped with Cowpea and Maize in Southern Guinea Savanna of Nigeria

“…Many studies of cereal/legume intercropping have shown that the quantity of N fixed by the legume depends on such factors as the morphology, density, and competitive ability of the legume (Ofori & Stern, 1987), the effectiveness of the rhizobia symbiosis and the system of intercropping (Rerkasem, Rerkasem, Peoples, Herridge, & Bergersationen, 1988). Intercropping of grain legumes generally results in the legume deriving a greater proportion of its N from N fixation than when grown alone, but legume dry matter production and N accumulation are usually reduced because of competition from the companion crop (Giller, Ormeshe, & Awah,1991).…”

Enhancing crop legume N2 fixation through selection and breeding

“…Xylem sap was collected either as sap bleeding spontaneously under pressure from the stump of the intact root following decapitation of the shoot (root-bleeding sap), or under mild vacuum applied to freshly-harvested shoot segments (vacuum-extracted sap). The latter technique (Bennet et al, 1927;Bollard, 1953), facilitated the development of the ureide assay of N2 fixation from one with restricted application (glasshousegrown plants, analysis of root-bleeding sap; McClure et al, 1980) to an assay that could be applied to a wide range of species and field environments (Herridge, 1984;Herridge et al, 1987Herridge et al, , 1988aHerridge and Betts, 1985;Norhayati et al, 1988;Peoples et al, 1989a, b;Rerkasem et al, 1988).…”

“…Peoples et al, 1989b;Rerkasem et al, 1988). In the case of soybean, the following equations are used ): Pyix(%) = 1 .…”