Soil management for in-ground nursery
crops
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In-ground nursery stock producers must rely
on ground preparation and preservation in order to raise and harvest
healthy field stock. When nursery soils are managed correctly they
can continue to well into the future supporting many rotations of
stock production and ease of harvest.
Characteristics of good nursery soil
Nursery owners who have prepared their sites well with proper tillage,
amendments, and the proper use of cover crops, will be rewarded
with a soil that posses the following features:
| Loose
friable texture that crumbles well |
Rich
with slow release nutrients |
high
cation exchange capacity |
| Absence
of clods and under-laying hardpan below the plow depth |
Freedom
from crusting upon drying out |
Supports
beneficial fungi, bacteria, and earthworms |
A nursery soil exhibiting these characteristics will perform well
both in the short term and as well in the future (1).
Tilth
Soil tilth is typically defined as the physical condition of soil
related to the ease of tillage, suitability as a seedbed, and impedance
of seedling emergence and root growth (2). A soil possessing good
tilth has an array of different sized soil particles, loosely arranged
soil that there is excellent porosity. Tilth is influenced by the
moisture and content of the soil. A soil that is said to have good
tilth is one that one that withstands tillage well. In clay soils,
poor tilth results in poor response to tillage. When clay soils
are tilled during the wet months in late spring large clods can
be formed which can be very difficult to break up upon drying.
Soil texture
Soil texture is used to refer to the size of the individual soil
particles and the relative quantity of each size present (3). The
largest soil particles are referred to as sand, the intermediate
are known as silt, while the smallest are called clay. Soil structure
refers to how these soil particles are bound together into larger
particles called aggregates. If a nursery site has high percentage
of sand-sized particles it is referred to as a sand. If the percentage
of sand is less than the percentage of silt it is referred to as
loamy sand or a sandy loam. When the percentage of clay increases
it may become known as sandy clay loam or sandy clay. Figure 1.
describes soil texture in relationship to the proportion of sand,
silt and clay.
| Figure 1. Soil texture designation
from coarse to fine. |
| Sand
|
Loamy
sand |
Sandy
loam |
Fine
sandy loam |
Loam
|
Silty
loam |
Silt
|
Silty
clay loam |
Clay
loam |
Clay |
|
Coarse
|
|
Fine
|
A coarse textures soil will drain easier in the spring, but won't
be able to hold residual winter moisture during the hot summer months.
Conversely, a fine textured soil will hold more moisture during
the summer but will often be too wet to till or work with in the
spring. In addition a fine textured soil can split and crack during
dry weather. In soil
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Good soil tilth comes from good soil aggregation
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profiles it's not uncommon to find coarser textured layers near
the soil surface with gradually finer layers beneath. If the subsoil
has a high percentage of clay the soil is said to have a clay pan
layer. When the clay pan layer is near the soil surface tillage
practices can become considerably more difficult. A clay pan layer
can impede the natural downward movement of water thus potentially
harming the roots of perennial crops. When selecting a field site
for in-ground production, find a soil with at least 8-10 inches
of well-drained) profile (4).
Permeability
The term permeability is used to describe the relatively movement
of water through a soil profile. A nursery soil with a coarse texture
will have a very rapid permeability while a fine textured soil will
have a very slow permeability. A nursery grower will look for soils
that drain well during the entire year. However they will avoid
slowly permeable soils for the following reasons:
| Higher
clay content interferes with bare-root harvesting as soil will
stick to the roots. |
High
soil moisture content in the spring delays plant growth as the
soils are slow to warm up. |
| Soil
permeability during the period of new root development in the
late winter can encourage the development of soil pathogens
such as Phytophthora spp. root rot (5). |
High
soil moisture in the spring can interfere with spring tillage
practices. |
Field production practices
Soil texture and permeability plays key roles to a nursery manger
as they directly affect the ability of the site to either hold water
during a drought, or drain water in the spring after the winter
rains have diminished. A loam soil is generally preferred as it
possesses 50% sand, 20% clay, and 70-80% silt. Table 2 describes
the preferred soil texture for different types of nursery stock
production.
| Table 2. Nursery manager's preference
for different soil textures. |
|
Lighter texture preferred
|
Heavier texture preferred
|
| Bare-root
production growers raising stock such as seedling forest conifers
(6), or deciduous shade tree liners, prefer a lighter soil texture
in order to lift field stock during wet months without having
excess soil stick to the plant roots. |
In-ground
shade tree producers lifting stock at maturity with a tree spade
(7) prefer heavier soil to ensure that root systems remain intact.
|
| Pot-in-pot
nursery producers prefer lighter soil as it may reduce the need
for under-laying drain tile (8) beneath the socket pots. |
Fall-harvested
bulb growers (9) can utilize heavier, bottom ground as it cheaper
to rent or lease and they won't dig their stock until the dry
months of the fall. |
| Native
plant producers (10 ) will select better draining sites for
plants that cannot tolerate flooding. Alternatively, for their
true wetland species growers will seek out sites with heavier
textures. |
Herbaceous
perennial growers may prefer slightly heavier ground as it may
reduce the need for as much supplemental irrigation during the
drier summer months. |
Soil structure
Soil structure refers to the manner and stability of the sand, silt,
and clay particles that make up soil texture, and how they are bound
together into units known as aggregates.
 |
|
These "October Glory" Norway
maples are 2-year field grown shade trees which are 3 months
away from being dug up and sold as bare-root stock.
They have been raised on well-drained ground so that they
should "lift" easily.
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From a soil science perspective structured soils are typically
formed in undisturbed forested situations and native prairies where
the constant buildup of fallen leaves and needles, along with the
natural wetting and drying cycles, yield a rich fertile structure
of naturally crumbly soil. In the upper most layer of the soil profile
a whole plethora of microorganisms include fungi, bacteria, algae,
nematodes, along with earthworms have worked collectively to yield
a granular soil structure that allows water and new plant
roots to pass through freely. Nursery crop producers recognize
the excellent structure that these sites offer. Agricultural soils
that
have been repeatabley disked and cropped without additions of soil
amendments or cover crops between rotations, will often loose their
original aggregated structure (11). Overworked soils will loose
their total pore space and thus become compacted (12).
Organic matter
Soil organic matter is the most important factor contributing to
good structure (13). Organic matter can be derived from organic
residues (plant, animal, and microbial) in various stages of decomposition,
from true humic materials, and from live organisms, principally
microbes. Humus represents only a small portion of soil organic
matter. It represents the end product of organic matter decomposition
is relatively stabile.
In nurseries the majority of the organic matter stems from plant
residues. Two types of plant residues are most frequently discussed.
Cover and green manure crops can be grown on the nursery site before
and between rotations and then incorporated. Alternatively, amendments
derived from yard-debris compost, straw, bark, or sawdust can be
applied and worked into the site. No matter what the source of organic
matter, frequent additions are the best way to improve soil structure
and thus over-all tilth.
A soil high in organic matter will help water-stabile aggregates
which will help prevent clods from forming, will help improve water
infiltration and permeability. Tillage operations will be easier
and the chance for erosion will be minimized with 4-5% organic matter.
It is estimated that a soil with 4% organic matter in the plow zone
layer of the soil surface will contribute the equivalent of 210
pounds of nitrogen/per acre release over the growing season (1).
If this organic matter is allowed to be degraded through excessive
tillage, plowing when the soil is wet, or leaving the uncovered
during the winter without the use of cover crops supplemental nitrogen
fertilizer will be needed to sustain crop growth.
Erosion potential
In most soils 45-50% of the total volume is occupied by minerals
and organic matter. The remaining 50% consists of pore space which
typically consists of 25% air and 25% water (14). While the organic
matter only represents a small percentage (3-5%) of the soil of
the total soil volume, it is very important to soil fertility and
good soil structure (16). A well aggregated soil, such as a medium-textured
loam soil, will have large pore spaces between the mineral portions
to enable adequate soil moisture drainage during wet periods, but
will also have small pores hat will help retain moisture during
periods of drought.
A good well-aggregated soil will be able to absorb rain and store
it first in the larger pore spaces, and latter in the smaller pores.
However, on compacted, degraded sites very little of the water will
be absorbed. The majority of it will flow over the soil surface
as runoff. Under periods of intense rainfall erosion can carry soil
particles into lakes and streams, or across impervious surfaces.
While soil erosion may be a slow process that continue largely unnoticed,
it can also occur at a faster pace resulting in loss of topsoil,
physical crop damage, and contamination of adjacent sites and bodies
of water (15). The primary factors which contribute to raising the
erosion potential include:
|
Low organic matter levels |
Poor soil structure |
Absence
of vegetation |
| Steep
slopes |
Longer
gradients |
Lack
of conservation measures |
Compaction
Soil compaction is defined as the process of increasing the density
of soil by packing the mineral particles closer together. Air fill
pores are the first to be filled. If there is adequate soil moisture,
the resulting density will be even greater as the particles of silt,
sand, clay, and organic matter are compressed even tighter.
The immediate effect of higher soil compaction is restricted root
movement potential. Simply put, plant roots will explore air-filled
friable soil if given the opportunity, thus shunning the compressed
regions. With fewer roots, plants will have less ability to take
up water and nutrients. Total growth and development will be hindered.
The effects will be first noted on field grown nursery stock that
does not receive supplemental irrigation during the dry summer months.
The lack of root growth simply means the plants won't be able to
get enough water to thrive.
Overcoming soil compaction
There is no one single best strategy to reduce soil compaction.
If field managers should consider putting as much emphasis on preventing
compaction as they do in producing their crops.
A review of the following steps (16) is in order:
| Avoid
working on wet soils. The soil should crumble at the deepest
depth it is going to be tilled. |
Reduce
the number of trips over a field. |
Use
drip irrigation as opposed to overhead if possible. |
Sub-soil
in the fall when the soil is dry at the depth of shank. |
| Keep
the weight on an individual axle to below five tons. Use trailers
with tandem axles. |
Choose
radial tires where extra traction is needed. They have up to
27% more surface contact than bias ply tires of similar size
. |
Four-wheel
drive tractors have better weight distribution between axles.
|
Use
good crop rotations that include deep-rooted crops or cover
crops. |
| Use
cover crops between rows to protect against over-wintering erosion
potential. |
Limit
traffic to certain areas or rows. |
If
possible, use the same travel lanes each year. |
After
harvest consider adding composted manure, straw or other organic
products if they are not too costly. |
References
1. Sustainable
soil management. September 2001. Preston Sullivan. National
Sustainable Agriculture Information Service, Fayetteville, AR.
2.
Physical properties of forest-nursery soils: Relation to seedling
growth. 1984. B.P. Warkentin. In: M.L. Duryea, and T. Landis
(eds):
Forest Nursery Manual: Production of Bareroot Seedlings.
3.
Basic principles of soil fertility II: Soil properties. 2002.
V. A. Bandel, B. James, and J. Meisinger. College of Agriculture
and Natural Resources, University of Maryland. Factsheet 640.
4. Best
management practices for field production of nursery stock.
Tom Bilderback, North Carolina Cooperative Extension.
5. Floriculture
and ornamental nurseries: Phytophthora root and crown rots.
January 2002. University of California IPM Online, Statewide Integrated
Pest Management Program.
6.
Nursery site: Selection, layout, and development. F.E. Morby.
In: M.L. Duryea, and T. Landis (eds): Forest
Nursery Manual: Production of Bareroot Seedlings.
7. Starting
a commercial nursery in Ontario. July 2003. Christoph Kessel
- Plant Nutrition Specialist, Ontario Ministry of Agriculture and
Food.
8.
Nursery stock production using the pot-in-pot production technique.
2002. Hannah Mathers, The Ohio State University.
9. Sustainable
Cut Flower Production, February 2000. Lane Greer, Agricultural
Specialist, ATTRA--National Sustainable Agriculture Information
Service.
10. Selection,
production and establishment of wetland trees and shrubs. July
1999. Mel Garber, The University of Georgia College of Agricultural
& Environmental Sciences.
11. Soil physical structure. 1990. Henry Foth, Michigan State University,
author of: Fundamentals of Soil Science,
8th Edtion. John Wiley and Sons Press.
12. The compaction problem. Adam Newby, and James Altlund. Oregon
State University North Willamette Research and Extension Center.
In: American Nurseryman, March
1, 2004.
13. Nursery
soil organic matter: Management and importance. 1984. C.B. Davey.
In: M.L. Duryea, and T. Landis (eds): Forest
Nursery Manual: Production of Bareroot Seedlings.
14. Let's get physical: soil tilth, aeration and water. Fred Magdoff,
Harold van Es. In: Building Soils for
Better Crops, 2nd edition. Available from: Sustainable Agriculture
Publications, University of Vermont, Burlington, VT
15. Soil
erosion-causes and effects. 1987. Ontario Ministry of Agriculture
and Food. Agdex#: 572.
16. Best
management for horticultural crops. May 2004. Ontario Ministry
of Agriculture and Food.
First posted:
December, 2004.
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