The absorption and partitioning of N is determined by its availability and demand during the various phenological stages of
the crop. In two experiments conducted in rainfed areas of the Mediterranean climate region of central Chile, legume-wheat
(
Triticum aestivum
L.) rotations were compared to oat (
Avena sativa
L.)-wheat systems (with and without applications
of N fertilizer). The objective was to assess the contribution of legumes to the availability of soil N and N uptake by
the wheat crop following grain legumes. N mineralization and uptake, N use efficiency (NUE), and N uptake efficiency
(NU
pE) by wheat were evaluated at different phenological stages in 2010. Synchronization existed between accumulated
soil N mineralization and N uptake by the wheat. N uptake by wheat was higher in Experiment II (Andean foothill) than in
Experiment I (interior dryland). Grain yields after legumes ranged 60-110% and 72-103% of yields in the fertilized cereal
rotation (oat-wheat) in Experiments I and II, respectively. There was high correlation between soil N availability
vs. grain
yield (R
2 = 0.84 and 0.64) and N uptake vs. grain yield (R
2 = 0.55 and 0.64) for Experiments I and II, respectively. Rotations
with lupine (
Lupinus
spp.) and field peas (
Pisum sativum
L.) showed high NUE and NU
pE in Experiment I, and Experiment
II in pea. The lowest NUE was after oats with N fertilizers. It is concluded that wheat cultivated in both agro-ecological
areas after grain legumes or green manure was more efficient in N uptake and use than cereal, especially when the latter
was fertilized.
