Horticultural Crops
Understanding the Basics - Soil Management

Understanding the Basics

Horticultural crop growers share many of the same management concerns of other producers. Although horticultural crops vary substantially, they all require skilled management to produce a high quality product. These crops rely on intensive management of soil, water, nutrient resources and pest populations.

Soil Management

Soil is vital to all crop production, whether sod, vegetables or fruit. Healthy and productive soil helps crops develop good root systems and reduces crop stress caused by drought or excess rainfall. Intensive production of horticultural crops creates some unique challenges in soil management.

Soil erosion is a concern in many horticultural crops. Highly productive land is valuable and the supply is limited. Water and wind erosion can remove nutrients, other crop inputs, soil and organic matter. The crops, themselves, may also be damaged or stressed by erosion, increasing the possibility of disease. The following table shows a number of practices available to reduce or stop erosion.

Erosion control structures, such as berms and terraces, are covered in the Field Crop Production book.  

Soil erosion can be particularly destructive to horticultural soils: removing crop inputs, soil and organic matter and damaging or stressing the crop.

X = Effective Control Possible

The impact of wind erosion is often underestimated. If soil is visibly moving, more than 11 tonnes/hectare of soil is being moved.

Most horticultural crops leave soil exposed. Even relatively small amounts of residue can reduce wind and water erosion.

Tillage and residue management involves leaving some crop residues to protect the soil. Residue acts in two ways:

• It protects the soil from the impact of raindrops and the resulting movement of soil particles and crusting.
• It acts as small dams or windbreaks slowing the movement of wind and water across a field and reducing their ability to carry soil.

To protect soils, at least 20% residue cover should be left-but any amount will help. See the Field Crop Production book for a more detailed discussion of reduced tillage and equipment modifications.

A rye cover after processing tomatoes add organic matter, holds some excess nutrients and protects the soil over winter.

Cover crops are planted to protect the soil surface and to maintain soil structure. They also help tie up excess nutrients, add organic matter to soil and control pests. There is a variety of cover crops available. Some are suited for specific uses. You must know what you want from a cover crop when making the selection. Ask yourself the following questions:

• What kind of growth habit is needed? Do I need vigorous early fall growth as provided by oats, or vigorous spring growth as provided by rye? Is deep-rooting an important consideration? Or, am I looking for lots of top growth in mid-summer?
• Should the cover crop survive the winter or die out?
• Can it become a weed problem? What are the control measures?
• What is the cost, availability of seeds, planting method?
• Does it produce nitrogen (e.g. clover) or take up leftover nitrogen (e.g. rye)?
• Are there benefits to soil structure?
• Is the cover crop related to other crops in the rotation?
• Will pest problems increase or decrease as a result of using the cover crop? For example, certain plant parasitic nematode populations often increase under red clover while they decrease with alfalfa.

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S = Spring; ES = Early Summer; MS = Mid Summer
LS = Late Summer; EF = Early Fall; LF = Late Fall

Note: Seeding success dependent upon weather, particularly summer seedings.
*Varietal difference in cover crop species may affect nematode reaction.
**Rye-whole season rating would be higher (+++)
X = Exhibits this characteristic usually
? = Inconsistent in some locations
– = Not applicable

Nematode Rating Codes

^ = Poor or non-host
+ = Ability to host
O = Some cultivars are non-hosts

Windbreaks and wind barriers are covered in detail in the book on Farm Forestry and Wildlife Habitat Management. Wind barriers include a variety of possibilities, from short-term grain interseedings in muck crops to grass strips and fence-like materials to protect vegetables. Barriers reduce the speed of wind and lower its ability to carry soil. The area protected by a tree windbreak is about 10 times its height. The amount of protection provided by other types of barriers varies depending on height and the flexibility of the material.

Wind barriers reduce the speed and soil carrying ability of the wind. Tree windbreaks protect an area about ten times their height. Grass wind barriers are more flexible and can be pushed down by high winds, reducing the protected distance to five to seven times the barrier height.

Strip cropping involves planting strips or sections of a field with crops having different growth habits. For example, growers may alternate strips of early vegetables with later-seeded vegetables. Although management may increase, the soil surface is better protected.

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Soil Structure

Maintaining good soil structure is also a challenge for growers of intensively managed crops. Soil structure refers to how well soil particles are organized and held together as soil crumbs or clods. Structure influences the general health of the crop in the following ways:

• Water movement in and through the soil.
• The resistance of soil to erosion, crusting and compaction.
• A plant’s ability to grow a good root system and take up nutrients.
• Aeration.

A good root system is essential to production, allowing the plant to exploit soil water and nutrients.

Soil Compaction

Tillage and cultivation tend to break down soil clods and organic matter. Organic matter is the glue that holds soil particles together. Production of high-quality horticultural crops requires timely operations. Sometimes, this means tilling, spraying or harvesting on soils that are too wet. In addition, to be cost-effective, many of these operations have become highly mechanized. Running heavy equipment in wet conditions may cause soil compaction. Compaction means that the soil has become packed and pore spaces are reduced which decreases the soil’s ability to hold both air and water.

Scheduled harvest of perishable crops sometimes forces working on wet soils. Try to avoid compaction using other measures and plan to rotate away from the problem crops.

Reducing Compaction

• Avoid working on wet soils.
• Reduce the number of trips over a field.
• Keep the weight on an individual axle to below five tonnes. 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.
• Limit traffic to certain areas or rows. If possible, use the same travel lanes each year.

Tillage and crop roots usually break up shallow or surface compaction. However, deep compaction or plow pans can be more difficult to deal with. Deep-rooted crops and frost action may help. Research shows that frost takes at least three winters to reduce compaction, assuming that no further compaction has taken place. Deep tillage or subsoiling is a prescription treatment for the worst areas.

Given the soil conditions, this deep tillage implement is where it should be - parked. Subsoiling must be done properly, or problems can be made worse.

It is important to subsoil properly or compaction is just moved deeper:

• Know the depth of the problem.
• Work on soils that are dry to the level of tillage.
• Plant a deep-rooted cover crop to keep the soil open.
• Make changes in your practices to avoid future problems.

Subsoiling is only a temporary solution and does not remove what caused compaction in the first place.

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Soil Organic Matter

Soil organic matter is a very small part of the soil with a large role to play. Many soils used in horticultural production have soil organic matter levels between 2 and 4%. About 40 to 45% of the soil organic matter is very stable and resists decomposition. Another 40 to 45% is moderately stable. This portion is protected or held within soil clods and on clay particles and is very important to soil fertility, accounting for 40 to 50% of nutrients released each year. The remaining 10 to 15% is composed of living and dead organisms and decomposes easily.

Reducing tillage where possible will help to retain soil productivity by reducing soil compaction and erosion losses of soil and organic matter.

Growers can directly affect the organic content of their soils. Excessive tillage, soil erosion and poor crop rotation will speed loss of organic matter. On the other hand, there are a number of practices that maintain and improve organic matter:

• Good crop rotations that return a variety of residues to the soil.
• Use of cover and green manure crops that add plant material to soil.
• Reducing tillage where possible.
• Adding organic matter such as manure, compost and other wastes. It is important to know what is in the material, though, first. (Any field application of organic off-farm waste, e.g. food processing waste, requires a permit from Ministry of the Environment.)
• Reducing erosion losses of soil and organic matter.
• Keeping tillage shallow to prevent dilution of organic matter.                        
  

Organic matter is only a small portion of the soil, but it is very important to soil fertility and good soil structure. Maintaining adequate soil organic matter levels is crucial to consistent production of horticultural crops.

The Basics: Page 2

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