[Edited_by_A._Ciancio,_C.N.R.,_Bari,_Italy_and_K.(Bookos.org)

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J.D. DUTCHER ET AL.
without weed control growing in both irrigated and not irrigated situations produced
only 18.2 and 17.5% of the yield, respectively, that was produced by trees where
total weed control was maintained over the first 8 years of growth (Table 3). This
research also shows that mowing around newly planted trees, while controlling
annual broadleaf weeds, allowed perennial grasses like bahiagrass to grow, thus
robbing the young trees of fertilizer and moisture. Trees in the study that were
mowed only as a means of managing the orchard floor produced 35.6 and 21.4% of
the yield (irrigated and not irrigated respectively) produced by trees where total
weed control was maintained using registered herbicides. This research was
conducted using a treated area of 3 m(dia), centered on the tree row. The 3 m treated
area was arbitrarily selected for this study. Additional research conducted following
this initial study shows that weed-free areas of 3 m(dia) or greater maintained from
planting provided optimum growth and yield while areas of 1.8 m (dia) or less
reduced growth and eventual yield in the first 2 years of nut bearing (Patterson et al.,
1990). Although the significant and detrimental impact of weeds on pecan growth
and yield has been documented, weeds can also serve as a host for insect pests
(Norris & Kogan, 2005), and negatively influence concentrations of nutrients in
young pecan trees (Goff, Patterson, & West, 1991).
3. BENEFITS OF CRIMSON CLOVER AND LEGUMES USE IN PECAN
ORCHARDS
In the last 30 years, growers have started an integrated approach to weed control by
seeding the orchard with various cool season legumes. These are grown as
intercrops in the mowed strip or as cover crops over the entire orchard floor. The
intercrop and cover crop plants supply nitrogen, suppress weeds, improve the soil,
enhance beneficial insects and benefit wildlife. For centuries, legumes have been
used to enhance the fertility and structure of agricultural soils. Historical references
as far back as the Roman Empire refer to the benefits these plants can provide. Cato
the Elder (234–149 B.C.) suggested improvements to poor vineyard land by interplanting
a legume crop. This crop was then turned under before the plants set seed.
The Chinese have also used legumes to maintain soil fertility through centuries of
cultivation. Legume use was introduced to pecan orchard management in the early
twentieth century. Pecan producers quickly realized the benefits of such plants as
blue lupine, vetch, and crimson clover as winter cover crops for the orchard.
Proper orchard management occurs at two separate, yet connected levels. The
orchard floor influences the tree crop and its management based on the type of
vegetation or lack thereof found in the orchard. An efficient orchard floor cover does
not compete heavily with trees for moisture and nutrients and is compatible with
orchard insect populations. Weed competition with tree roots is significant
throughout the life of the tree. In a newly planted orchard, weed competition can
significantly reduce young tree survival and can stunt tree growth (Patterson, 2005a,
2005b). In the case of the mature orchard, vegetative competition can rob the soil of
water and nutrients intended for the crop, reducing tree growth and yield, while also
promoting alternate bearing. Pecan orchards generally consist of sod culture on the
orchard floor with a weed-free herbicide strip approximately 2–4 m wide along the