With renewed interest in legumes for green manures or as partial
summer fallow replacement crops, it is important to know water
requirements of these crops in semiarid agriculture. Our objective
was to evaluate seasonal water use by black lentil (Lens culinaris
Medikus cv. Indianhead), a potential fallow replacement crop, and
to relate water use to parameters useful as soil water management tools.
We measured evapotranspiration (ET) from two precision weighing
lysimeters located on a Williams loam (fine-loamy, mixed Typic Argiboroll)
near Sidney, MT. The lysimeters were in adjacent 180- by
180-m fields in a typical strip-crop environment of the semiarid northern
Great Plains. Bowen ratio estimates of ET were also obtained.
Lentil was seeded no-till into wheat (Triticum aestivum L.) stubble on
one lysimeter field in 1993, and the other was left in chemical fallow.
Seeded and fallow fields were rotated in 1994. Water loss by ET from
lentil and fallow lysimeters was the same ( 25 mm) for 3 wk following
seeding. Plant height was related to growing degree days (GDD) in
both years. Cumulative ET was related to GDD for both years until
about 800 GDD, corresponding to nearly 300 mm ET. Deciding how
much water to sacrifice (with hopes of recovery during the noncrop
period) becomes a matter of judgment about probable rainfall. At
full bloom ( 2 Mg ha' dry matter production), the lentil crop used
about 50 to 70 mm more water than fallow. Probably no more than
50 mm of water loss above that from fallow should be sacrificed if a
grain crop is to be seeded the following year. From a practical standpoint,
because plant height was closely related to both GDD and
cumulative ET, it is plausible that a simple measure of lentil height
(about 350 mm maximum) can give sufficient accuracy for determining
when lentil growth, as a partial summer fallow replacement crop in
a semiarid climate, should be terminated
