Is nitrogen transferred between field crops? examining the question through a sweet-blue lupin ( Lupinus angustifolius l.)-oats ( Avena sativa) intercrop

One of the often quoted advantages of intercropping over monocropping is higher productivity. This has been attributed largely to the use of the N transferred to the non-N sub(2)-fixing crop from the associated N sub(2)-fixing crop. However, the postulated increased productivity and N transfer need careful examination as contradictory results have also been reported. The data of Vasilas and Ham for example showed that the yield of non-nodulating soybean was not increased by intercropping with a N sub(2)-fixing soybean. Similarly, several studies have failed to demonstrate significant transfer of N from a N sub(2)-fixing crop to an associated cereal. Vasilas and Ham reported that N was transferred only at the higher of two N rates used, raising the question of whether N is transferred under some conditions but not others. This is a very important question, given the agronomic importance of N transfer. It appears that a convenient point to start re-examining N transfer is to select a simple system that is most likely to stimulate N transfer and its detection, e.g. using a high N sub(2)-fixing crop and thus with a high potential to transfer some of its fixed N to a cereal, especially when both are grown in sand or in a low-N soil; under these circumstances the postulated growth enhancement and N transfer should be high and easier to detect than when soil N is high.