Production: Soil Management for In-ground Nursery Crops

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
• Absence of clods and under-laying hardpan below the plow depth
• Rich with slow release nutrients and high cation exchange capacity
• 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 seed-bed, 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.

Coarse										Fine
Sand	Loamy sand		Sandy loam	Fine sandy loam	Loam	Silty loam	Silt	Silty clay loam	Clay loam		Clay

 

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 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 (4). profile.

Permeability

• 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. From a soil science perspective structured soils are typically formed in un-disturbed forested situations and native prairies where the constant build-up 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 micro-organisms 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 re-peatably disked and cropped without additions of soil amendments or cover crops between rotations, will often loose their original aggregated structure (11). Over-worked 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 soil organic matter levels,
• Poor soil structure,
• Absence of vegetation,
• Steep slopes, and 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.

Over-coming 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 over-head 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. Best Management Practices for Field Production of Nursery Stock. Tom Bilderback, North Carolina Cooperative Extension.
4. Floriculture and Ornamental Nurseries: Phytophthora Root and Crown Rots. January 2002. University of California IPM Online, Statewide Integrated Pest Management Program.
5. Nursery Site: Selection, Layout, and Development. F.E. Morby. In: M.L. Duryea, and T. Landis (eds): Forest Nursery Manual: Production of Bareroot Seedlings.
6. Starting a Commercial Nursery in Ontario. July 2003. Christoph Kessel – Plant Nutrition Specialist, Ontario Ministry of Agriculture and Food.
7. Nursery stock production using the pot-in-pot production technique. 2002. Hannah Mathers, The Ohio State University.
8. Specialty Cut Flower Production and Marketing. 2006. Janet Bachmann, NCAT Agriculture Specialist, ATTRA–National Sustainable Agriculture Information Service.
9. Selection, Production and Establishment of Wetland Trees and Shrubs. July 1999. Mel Garber, The University of Georgia College of Agricultural & Environmental Sciences.
10. Soil physical structure. 1990. Henry Foth, Michigan State University, author of: Fundamentals of Soil Science, 8th Edtion. John Wiley and Sons Press.
11. The compaction problem. Adam Newby, and James Altlund. Oregon State University North Willamette Research and Extension Center. In: American Nurseryman, March 1, 2004.
12. 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.
13. Let’s get physical: soil tilth, aeration and water. Fred Magdoff, Harold van Es. In: Building Soils for Better Crops, 2^nd edition. Available from: Sustainable Agriculture Publications, University of Vermont, Burlington, VT
14. Soil Erosion – Causes and Effects. 1987. Ontario Ministry of Agriculture and Food. Agdex#: 572.
15. Best management for horticultural crops: Nursery. May 2004. Ontario Ministry of Agriculture and Food.

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