TheImprovement ofTropical and Subtropical Rangelands

170 IMPROVEMENT OF TROPIOAL AND SUBTROPIOAL RANGELANDS
and climatic conditions. Seeding is done by an inexpensive broadcasttype
lIeeder mounted on the tractor or on the towing tongue of the
imprinter, which allows the imprinter being towed to press the seed
into close contact with the lIOil. The basic imprinting pattem creates
a "runoff" groove that channels water to the seedbed groove where
germination and plant growth can occur even under less-than-normal
rainfall.
The machine rolls over and crushes the brush including individual
plants with a basal diameter of up to 10 cm, although it is most
effective on stems of leu than 5 cm. The destruction of dense old
brush is not as effective as with more specialized machines designed
specifically for total brush removal; however, IIOme brush is effectively
killed, and the remainder is sufficiently damaced to delay regrowth
until after the critical period of successful establishment of the new
grass seedlings. At that time, the recuperating brush encounters
strong soil moisture and nutrient competition from the new grass.
The land imprinter creates an additional benefit of mulching the
existing vegetation into the soil to help retain moisture, provide soil
aeration, and contribute to soil structures and nutrients. When the
land imprinter is operated on very dry soil, crushing stems into the
soil is leu effective than on moist soil.
'baDBplantlng
Plants grown in containers or nursery beds can be transplanted
to the field. Planting material includes plants propagated from seed,
stem layerings, root suckers, root cuttings, and shoot cuttings. The
young plants should be about 75-100 days old when they are transplanted:
they should not exceed 20-25 cm in height nor have a
diameter of over 5 mm at the neck. In arid zones, the resistance of
nursery plants should be conditioned by low and infrequent irrigation
at least a month before they are planted out. The above-ground part
of the plant should be cut back to 20 cm (hardwoods and grasses, but
not conifers) and, where appropriate, roots should also be trimmed.
Planting Container-Grown Plantl
The use of transplants, with roots growing into the planting
medium, ensures the greatest degree of success and the least interruption
of growth after planting. It is especially suitable for planting
very young and tender plants. The techniques employed involve