| ||||||||||||||||||||
Chickpea, organic P and maize productivity
Although monoculture is by far the most widespread system for crop growth, inter-cropping, that is the growth of alternate rows of different crops, is finding increasing application. In the most frequently used arrangements, a legume is intercropped with a cereal. The available evidence suggests that this leads to increased productivity of the cereal while it has been claimed that the leguminous crop may also benefit. Intuitively, we may suppose that the cereal may be advantaged by an increased N-supply and there are certainly data to support this idea. However, there is also evidence that intercropping may make P more available, particularly from organic sources. This possibility has been studied by a joint Australian–Chinese group (Li et al., pp. 297–303). They investigated the effects on maize (Zea mays) of intercropping with chickpea (Cicer arietinum), in laboratory-scale growth experiments both in soil and in hydroponics. In the soil experiments some of the plants were grown with a solid, impermeable barrier between the maize and chickpea root systems. Ca-phytate was used as an organic P source. The results were very clear: the presence of chickpea plants led to significant increases in P uptake in the maize plants, except where the root systems were separated by solid barriers. Chickpea plants were much more able than maize to mobilize P from Ca-phytate. Further, the acid phosphatase activity of chickpea roots was two- to three-fold greater than that in maize roots. This difference was paralleled by differences in acid phosphatase activities exuded to the rhizosphere. However, the authors are careful, in the absence of direct evidence, to avoid the conclusion that the increased mobilization of P was a direct result of the greater acid phosphatase activity. As they rightly point out, this can only be properly demonstrated by comparing the efficacy of chickpea cultivars differing markedly in acid phosphatase activity.
Professor J. A. Bryant, University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
| ||||||||||||||||||||