Root Behavior and Nitrogen Balance Sheet in Four Pigeonpea-Based Intercropping Systems on a Deep Alfisol in the Semi-Arid Tropics.

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An experiment was conducted to study the root behavior and nitrogen (N) balance in pigeonpea-based Intercropping systems during the 1993 rainy season. Five crops (pigeonpea: ICP 1-6, sorghum: CSH 5, pearl millet: ICMV 221, groundnut: ICGS 11 and cowpea: EC 82-7) were used. All the plots received uniform basal application of 25 kg N ha-1 as urea and 20 kg P2O5 ha-1 as single superphosphate. The fractional contribution of N derived from air (%Ndfa) in legumes and from fertilizer (%Ndff) was determined by the natural 15N abundance and 15N tracer methods, respectively. A minirhizotron was used for the measurement of root length density (RLD) nondestructively. The RLD was significantly higher in cereals and pigeonpea/cereal than in legumes and pigeonpea/legume intercroppings. There was no significant difference in total N content among sole and intercropped pigeonpeas. The %Ndfa was significantly higher in pigeonpea intercropped with cereals than with legumes, suggesting that cereals are able to deplete soil N massively due to their high RLD and enhance the dependency of pigeonpea on biological N fixation. It is speculated that the enhancement of %Ndfa of intercropped pigeonpea depends on the extent of competition for the uptake of soil N in the deep Alfisol soil by roots of companion crops at the vegetative growth stage.
日本熱帯農業学会の論文