Environmental Implications of N Fixation by Soybeans

Abstract

The objective was to measure inorganic N removal from soil by soybeans (Glycine max L.) grown at different N levels. Nodulating and non‐nodulating isolines of ‘Clark’ soybeans were planted on Flanagan silt loam in 1972 and 1973. Fertilizer rates of 0, 112, 224, and 448 kg N/ha as Ca(NO3)2 enriched with 1% 15N were applied.Symbiotically fixed N decreased from 48 to 10% of the total N in the above‐ground plant as applied fertilizer N increased from 0 to 448 kg/ha. Net removals of N by soybean grain were 61, 109, 135, and 149 kg/ha at 0, 112, 224, and 448 kg fertilizer N/ha rates, respectively.Corn (Zea mays L.) grain grown on adjacent plots removed 62, 123, 129, and 133 kg N/ha at fertilizer N rates of 0, 112, 224, and 336 kg/ha, respectively.The study indicates that soybeans are good scavengers for inorganic N in soils. Inclusion of net N removal by soybeans in the calculated N removed by nonleguminous crops in Illinois from 1945 to 1973 increases net crop N removal by approximately 37%. Added fertilizer N has exceeded the N removed by the harvested portion of Illinois crops in only 5 years since 1945, all 5 of these occurring after 1965.

Cropping System Effects on No3–n Loss With Subsurface Drainage Water

“…This shows that plots under soybean were able to leach NO 3 -N with subsurface drainage flow as much as corn plots. A soybean crop typically accumulates 25% to 50% of its N from atmospheric N 2 fixation (Johnson et al, 1975;Harper, 1987) and uses the residual N and mineralized N from the soil for the majority of its N requirement (Olsen et al, 1970). Cambardella et al (1999) reported that substantial quantities of applied N fertilizer become incorporated in soil organic matter and remineralize in the subsequent years.…”

Réponse du soya à la fertilisation minérale en éléments majeurs NPK sur des sols classés de riches à excessivement riches en phosphore ou en potassium des Basses Terres du Saint-Laurent

“…Les conditions abiotiques de croissance des régions centrales de l'Ontario sont relativement similaires à celles des Basses Terres du Saint-Laurent. Buttery (1986), Johnson et al (1975) et Welch et al (1973) ont aussi démon-tré qu'un apport en fertilisation azotée incorporé au semis ne permettait pas d'augmenter les rendements en grains pour des soyas préalablement inoculés. L'effet de l'azote (N) est généralement non significatif sur les cinq autres variables mesurées.…”

“…Aux États-Unis, Johnson et al (1975) et Welch et al (1973) ont démontré qu'un apport en fertilisation azotée incorporé au semis n'augmentait pas les rendement en grains du soya préalablement inoculé. Lamb et al (1990) et Bhangoo et Albritton (1976) ont toutefois remar-qué que le soya pouvait répondre à la fertilisation azotée si les contenus en matière organique ou en nitrates résiduels des sols disponibles pour la plant étaient faibles ou insuffisants.…”

Nitrogen Fixation in Sugar Cane Litter

“…The released N can stimulate the next crop, but it may also be leached in the interim between annual crops. The result of these differences is that even though the grain legume fixes 5 to 10 times the amount of nitrogen fixed in the cane system the grain legume tends to deplete soil fertility (Harmesen and van Schreven, 1955;Johnson et al, 1975), while soil fertility is increased under cane. Other than cane, lowland rice is possibly the only crop under which soil fertility is increased or maintained at high levels in humid tropical regions.…”