Healthy soil is a critical resource to manage on a small farm.
This page explore some of the historic consequences of farming practices in New Zealand and some of the alternative practices that could be implemented to avoid these issues.
This page explore some of the historic consequences of farming practices in New Zealand and some of the alternative practices that could be implemented to avoid these issues.
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Compaction
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Soil compaction is rearrangement of soil particles and reduction in macro-porosity and total pore space by stresses. Stresses can be external such as those from machinery or internal from increasing pore water suction during drainage and drying. The main cause of subsoil compaction on agricultural soils is cropping machinery. Other stresses may come from tillage, stock trampling and overburden pressure. Compact soils restrict crop and pasture production and increase nutrient leaching and emission of greenhouse gasses. Compaction is the change of a soil volume by compression and shear forces to increase bulk density and decrease porosity - the air is squeezed out of larger soil pores. Shear forces are caused by the traction forces of wheels, hooves and tracks and mainly confined to the surface soil. Compression forces affect surface and subsurface soil and have the greatest influence on soil that is moist and soft. |
The main processes of compaction are:
The stresses exerted on a topsoil depend on the nature of the object imposing the pressure. Dexter and Tanner (1973) quoted the maximum pressures generated by animals and tractors as:
Stress in megapascals (MPa)
Stock trampling is a significant cause of compaction, especially in the surface horizon of finer textured soils, but effects are confined to the upper 15cm of the profile.
- Compression: Packing together of soil particles by relatively vertical forces, for example, under wheels tracks or animal feet.
- Shearing: Deformation of the soil mass, resulting from opposing horizontal forces, such as under spinning and slipping tractor wheels or hooves and implements such as ploughs.
- Smearing: Realignment of soil particles in a thin layer from random to parallel orientation under the base of mouldboard ploughs and spinning wheels (extreme shearing).
The stresses exerted on a topsoil depend on the nature of the object imposing the pressure. Dexter and Tanner (1973) quoted the maximum pressures generated by animals and tractors as:
Stress in megapascals (MPa)
- Horses and cows 0.16-0.39MPa
- Sheep/humans 0.06-0.10MPa
- Small tractors 0.03-0.10MPa
- Large tractors (2-axle) 0.1-0.2MPa
Stock trampling is a significant cause of compaction, especially in the surface horizon of finer textured soils, but effects are confined to the upper 15cm of the profile.
Tilling Soil
Tillage is the term used to describe the agricultural preparation of the soil by digging it and turning it over. So why are the farmers so fond of this destructive practice? Well, they found that when you first dig up the soil, fertility goes up, and plants grow better. The reason is that the tiny little bodies of all the soil organisms that have just been killed by digging break down, releasing their nutrients to the soil. The catch is, it only works once, and then your soil is sterile and the plants are worse off, and they become more prone to diseases, and require even more fertilizer than they normally would.
No-dig Gardening
We can add organic matter directly to the soil surface, such as manure, compost, straw, leaves etc. Garden waste such as prunings from trees and shrubs can be fed into a mulcher to break them down into smaller pieces, and then spread over the soil as a mulch.
Adding a layer of organic matter over the soil, in a layer approximately 5cm-15cm (2”-6”) thick is in effect ‘sheet composting’, where the garden beds become large composting areas. By the action of earthworms, bacteria, fungi and insects, the organic matter is slowly broken down and released into the soil, providing nutrients to the garden. Because the soil is not disturbed, a stable soil ecosystem is created, and plant health is improved. Moisture is also better retained due to the mulching, and the organic matter in the soil works like a sponge to better retain the moisture in the soil. The mulching also prevents soil erosion, stops runoff of rainwater across the surface, and assists the rainwater to percolate into the soil. The earthworms will create channels in the soil, which will help both water and air to penetrate into the soil.
Adding a layer of organic matter over the soil, in a layer approximately 5cm-15cm (2”-6”) thick is in effect ‘sheet composting’, where the garden beds become large composting areas. By the action of earthworms, bacteria, fungi and insects, the organic matter is slowly broken down and released into the soil, providing nutrients to the garden. Because the soil is not disturbed, a stable soil ecosystem is created, and plant health is improved. Moisture is also better retained due to the mulching, and the organic matter in the soil works like a sponge to better retain the moisture in the soil. The mulching also prevents soil erosion, stops runoff of rainwater across the surface, and assists the rainwater to percolate into the soil. The earthworms will create channels in the soil, which will help both water and air to penetrate into the soil.
Erosion
| erosion_management_nz.pdf |
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WHAT IS SOIL EROSION?
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CAUSES OF SOIL EROSION
Erosion occurs when farming practices are not compatible with the fact that soil can be washed away or blown away. These practices are:
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Protection from Trees
Trees reduce the effect of erosive forces using their root systems and foliage. Tree roots begin as thick stems that branch into fine filaments to create a network of flexible tendrils that help stabilize the soil around the tree and hold it in place. The leaves and branches of trees create a flexible screen that reduces the force of wind and rain in the surrounding area. You can increase the beneficial impact of trees on areas with eroding soils by planting them in groups.
The root systems of most trees consist of several large roots that branch out into many smaller roots. The root systems of many trees extend out into the surrounding soil far beyond their branches These roots hold the soil in place and improve the drainage of the soil. The roots prevent soil compaction and help water soak into the ground instead of flowing over its surface. Tree roots tend to grow more deeply than other plants and provide a greater resistance to erosion on hillsides than grasses and other small plants.
The root systems of most trees consist of several large roots that branch out into many smaller roots. The root systems of many trees extend out into the surrounding soil far beyond their branches These roots hold the soil in place and improve the drainage of the soil. The roots prevent soil compaction and help water soak into the ground instead of flowing over its surface. Tree roots tend to grow more deeply than other plants and provide a greater resistance to erosion on hillsides than grasses and other small plants.