TheImprovement ofTropical and Subtropical Rangelands

162 IMPROVEMENT OF TROPIOAL AND SUBTROPIOAL RANGELANDS
seedling establishment are tenuous. On steep slopes or sites inaccessible
to drills or other equipment, broadcast seeding may be used. In
this case, a doubled seed rate of 500 PLS per m 2 is recommended.
Planting DeptA Proper depth of seeding naturally depends
upon the species being planted. Optimal depth of seeding is roughly
4-7 times the diameter of the seed. Seeding equipment should be
used that provides pOllitive seed placement at the desired depth.
More stands are lost because seeds are planted too deep rather than
too shallow.
Timing The most desirable time to seed nonirrigated areas is
immediately before the season ofthe most reliable rainfall, and when
temperature is favorable for plant establishment.
Seed Distribution Uniform seed distribution is essential. Skips
and missed strips should be avoided. Seeding equipment must be
checked frequently to assure it is working properly and is not plugged.
Microenvironment In many areas, soil moisture is insufficient
for germination and seedling establishment. Germination and establishment
are also affected by high soil temperatures. Greater
moisture availability and soil temperature regulation can generally
be accomplished through practices such as mulching, summer fallow,
and the use of various water-harvesting devices (Herbel, 1972a). In
some instances, additional soil treatments might be necessary (Herbel,
1972b). For example, where heavy crusts have formed over
medium- to heavy-textured soils in arid and semiarid areas, the
arid-land seeder (figure 7-7), or similar implements, can be used to
improve soil-moisture relationships (Abernathy and Herbel, 1973j
McKenzie and Herbel, 1982).
Seedbed Preparation The major objectives for preparing seedbeds
are: (1) to remove or substantially reduce competing vegetation,
(2) to prepare a favorable microenvironment for seedling establishment,
(3) to firm the soil below seed placement and cover the seed
with loose soil, and if possible, (4) to leave mulch on the soil surface
to reduce erosion and to improve the microenvironment.
Fertilization Where water is not a limiting factor, the addition
of a nitrogen-phosphorus plant fertilizer in bands near the seed zone
may be helpful in plant establishment. Broadcasting fertilizer is not
advisable, because it will overstimulate competing plants.