Soil Beneficials for Orchards

Table of Contents

1. Introduction
2. Fungi
3. Bacteria
4. Actinomycetes
5. Algae
6. Macroscropic
7. Earthworms

Introduction

In biologically active soil, the soil life can account for over 4 tons per acre (0.5%) in the plow layer. This represents a large portion of the soil organic matter pool in some soils.

Fungi

At the microscopic level there are fungi, bacteria, actinomycetes and algae in most soils. Populations of these microscopic organisms vary depending upon soil type, pH, soil cover or crop rotation and tillage. Fungi make up the largest amount of living material after plant roots. They are intolerant of intensive tillage. Fungi help make soil nutrients available to plants and are greatly involved in decomposition of organic matter. There is a particular family of fungi called VAM (vesicular arbuscular mycorrhizae) that is symbiotically involved with plant roots, particularly in perennial crops like orchards and undisturbed soils, that can help to increase the absorptive area of plant roots up to a thousand-fold. Research has shown that these fungi can enhance the uptake of phosphorous in low phosphorous soils.

| Top of Page |

Bacteria

Bacteria number in the billions in most soils. They are important for maintaining good soil quality and fertility. Nitrogen-fixing bacteria are particularly important and are associated with plants such as alfalfa, peas, beans and some trees like locusts.

| Top of Page |

Actinomycetes

Actinomycetes are less well-known but play an important role in the decomposition of soil organic matter. They are particularly abundant in low pH and droughty soils, characteristics of many of our highly productive horticultural soils.

Algae

Algae help to decompose organic matter. These are most commonly seen in poorly drained soils, and often they become visible around wet areas. However, algae is found throughout the soil at a very shallow level.

Macroscopic

Macroscopic soil animals include arthropods, earthworms and rodents. Arthropods represent a wide variety of soil-dwelling insects, spiders and mites. Micoarthropods are extremely numerous in undisturbed soils or soils with perennial crops with populations over 1 million per square metre. In contrast, typical field crop soils have much lower levels (75 000/m₂) due to the decrease in soil organic matter from tillage and changes in microclimate from cropping patterns. These micro arthropods are involved in the decomposition of plant residues, but they also stimulate fungal growth and microbial activity. A few of these creatures are pests but some also provide some biocontrol of nematodes.

| Top of Page |

Earthworms

The earthworms in Ontario are not native to the province. The glaciers that receded over 10 000 years ago scoured and deposited the parent materials for our soils, leaving little or no life behind. Earthworms came with the settlers on seed and plants and on earthen ballast from their ships. There are essentially two types of earthworms:

• shallow-dwelling worms like fish worms that are small, may be red, grey or almost transparent, usually found in the top four to six inches of soil
• larger, deep-soil-swelling dew worm (Lumbricus terrestris).

Earthworms can number in the thousands per square metre under a pasture or as little as 10 per square metre under an extensively in the soil, creating macropores which improve drainage. The soil passes through the gut of the earthworm and the nutrient-rich feces are plastered along the burrow walls. Often plant roots make use of these burrows, due to the ease of rooting, good aeration and abundant nutrients. On the soil surface, dew worm burrows can easily be identified by the pile of casting and crops residues also called middens.

Gulls are often blamed for the loss of earthworms during plowing but studies have shown that the tillage action actually has a greater detrimental effect than these birds. The gulls eat injured worms and other soil animals for the most part. Earthworms are most active - eating, breeding etc. - during the spring and fall. Rodents, like earthworms, pass organic matter through their gut when they burrow and feed in the soil. The fecal matter is rich in nitrogen, phosphorous and potassium.

Orchard soils differ from soils used for annual crops in regards to soil life and their activity. The reduction in tillage with a perennial crop, and the presence of canopy shading of the ground, creates a much different environment than cash-cropped field. Generally, populations of most soil plants and animal will be higher due to the lack of disturbance. Concerns over pesticides are often expressed for soil life, however studies have shown that earth-moving and tillage have far greater effects than pesticide applications.

Ground cover management can have an impact, however. Frequently tilled row middles will have lower number of earthworms due to damage to the worms from the tillage implements. Cover crop middles will tend to have slightly higher earthworm numbers as a result of the shading and return of organic materials. In contrast, earthworm numbers under dense sod middles are lower. Monitoring of earthworm number in some orchards in southwestern Ontario indicated significantly high numbers of earthworms in the herbicide strip immediately under the trees. Leaf little, shading, and in some cases irrigation may have helped to increase these numbers.

In perennial crops like orchards, earthworms play an important role in incorporating organic and other surface applied materials, thereby increasing fertility. Earthworms gradually churn and mix the soil and larger species also create long, large burrows. Since there is little or no tillage to disrupt the burrows, they act as drains, improving the natural drainage of the soil.

Your soil is alive. A measure of the health of your soil is the number and diversity of soil life within it. A healthy, diverse soil is important for maintaining soil structure, water infiltration and movement, good aeration and efficient nutrient cycling, - all important components in crop production.