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 Soil Management: Drainage, Irrigation, Tillage, and Cultivation
Excerpt from The Soul of Soil, by Joe Smillie & Grace Gershuny
In planning the most appropriate soil management practices, the first factor to consider is soil moisture and soil aeration. The most sophisticated fertilization program will give scant return if the soil does not have a proper moisture/air balance. This balance will not be present if the land is poorly drained or does not have adequate moisture. Organic farming relies on conventional drainage practices if these are ecologically sound, complying with marshland conservation measures. Organic management in arid areas can even drought-proof soil to some extent. Tillage practices will vary depending on the soil and climate, but the principle is to preserve organic matter in the top horizon. In situations where perennial crops are being raised, permacultural practices largely replace annual tillage and most cultivation. Organic farmers have been the leaders in developing innovative mechanical cultivation systems for weed control, but that only serves to supplement control based on a well-tuned crop rotation.
Drainage
Farming in areas where the water table is high may require subterranean tiling with perforated pipe or a grid work of ditches. Heavy clay soils and those with subsoil hardpan layers may require special measures, such as sub soiling with a bulldozer, to allow better water and root penetration. Many soils that drain poorly simply require ecological management to improve percolation and break up plow pans and compaction, but structural problems may require drainage. Consult your Extension or Soil Conservation Service for the most appropriate local services.
Irrigation
It is not within the scope of this book to discuss the ecological ethics or practical implementation of irrigation in organic farming systems. Suffice it to say that if irrigation is appropriate on any farm it should be managed so that water use is optimized. In practice that would mean that flood irrigation would not be as acceptable as drip irrigation. The principle of ecological management is to improve the water-retention capability of soils and design the farming system to optimize the water cycle. This is accomplished in arid areas by following guidance offered in systems such as permaculture, holistic management or key line management, not in rerouting rivers to desert areas.
Tillage
The function of tillage is to incorporate organic matter and mineral fertilizers into the soil, aerate the soil, improve water permeability, control weeds, and prepare a seedbed. Since all tillage destroys organic matter and causes compaction to some degree, tillage systems should be designed for minimal use and damage to soil structure.
A tillage system should work crop residues and other organic matter into the topsoil, where, in the presence of bacteria and other life forms, it can be digested. Some sort of vegetative cover or litter should be left on the soil during the northern winter, southern dry season, or tropical rainy season. A properly managed tillage system creates a seedbed where carbon dioxide, oxygen, nitrogen, and water circulate through the soil, fostering the biological processes that create soil fertility and plant growth.
Seedbeds are often created in a way that damages soil structure, resulting in erosion, compaction, and organic matter oxidation. For example, one common conventional method is fall moldboard plowing, spring discing, and a final harrowing. The plow can create a hardpan with annual use, bury organic matter and living topsoil in an anaerobic zone, allow bare subsoil to erode by wind and water, and obstruct the capillary action of water. Spring discing breaks down the clumps, but it also causes compaction especially in wet conditions. The field may look good after the final harrowing, but not without great expense to soil tilth.
Properly designed tillage tools avoid these problems. Although, the moldboard plow is useful to turn a heavy sod, it is inappropriate for most farms. New types of plows, such as the English paraplow, Australian keyline plow, and the German bio-plow, can accomplish plowing tasks without the detrimental effect of conventional plowing. Many organic farmers base their system on the chisel plow for deep tillage in the fall and offset discs for seedbed creation in the spring. Rotovators are used by a number of farmers, especially market gardeners. While they do mix organic matter into the top layer, they can create a hardpan and leave the soil to fluffy. They are best employed on a sandy soil, with a subsoiler or heavy chisel used annually to break up the hardpan.
In response to tillage problems, and in recognition of the need to nurture a living soil, a number of combination tools such as the Lely Rotera, Glencoe Soil Saver, Landoll Soil Master, and Weichel Terravator have been developed. These tools have their proponents and have grown in popularity since the early 1980s.
The other development in conservation tillage tools has been the Ridge Till and Zone Till systems. These tools developed and promoted by companies like Buffalo Farm Equipment, create field ridges for overwintering and spring planting. Ridging seems to decrease erosion, create a dynamic seedbed, and allow for easy weed control. No-till systems usually rely on herbicides and hence are unsuitable for organic farming.
Ecological tillage is as much a question of timing as it is one of proper equipment. Only experience with your own soil and climatic conditions, combined with knowledge of equipment capabilities, will lead to an appropriate system for your farm.
Cultivation
The main reason for cultivation is weed control. Cultivation also breaks up soil crusts and stimulates biological activity through aeration. However, at the same time it oxidizes organic matter and damages soil structure.
Weeds are a major challenge for organic farmers. Weeds are controlled but never eliminated under ecological management systems. Knowing the life cycle of problem weed species can enable you to decide on the best method of control. A well-tuned crop rotation is the basis of ecological weed control. Aspects of rotations include:
• Mixing sod and row crops in rotation, alternating control methods for warm-and cool-season weeds, and matching crop needs to nutrient levels - especially nitrogen - so that excesses do not spur weed growth.
• Green-manure smother crops like buckwheat, and allelopathic crops like rye (which excrete exudates that suppress competition).
• "Living mulches" or legume intercrops that smother weeds as well as fixing nitrogen and adding organic matter. Sometimes weeds themselves can function as a mulch if they do not set seed or spread.
• In perennial crop settings timely mowing can control weeds if shading or competition do not.
• Animal grazing, especially when optimized with movable fencing.
Biological controls, such as weed-eating insects and weed diseases, are becoming more popular as chemical companies diversify into bio-rationals and introduce ecological products. Plastic mulch of varying colors and degradability are also allowed to organic farmers with restrictions that include proper postseason cleanup.
These practices do not usually eliminate the need for some mechanical cultivation to control weeds; many farmers feel that there is no substitute for fast-moving steel. Innovative farmers and manufacturers keep developing increasingly effective equipment. One of the most popular implements for organic farmers is the rotary hoe. This is a tool bar mounted with circular steel-tipped wheels on individual springs. It is pulled at high speed over crops when they are two to three inches high and kicks out weed seedlings without harming established plants. Farmers have continued to modify this tool to their needs, some welding on heavier tips and trash guards to convert it to heavier tilling functions, others adding a second tool bar and holes to double its action and cut down on field trips.
Harrows have also been modified and put to uses other than finishing the field for planting. For example, light harrows are used to rake a field after planting (a procedure called "blind harrowing") to disrupt weed growth. Row cultivators have also undergone a radical change in design. The Bezzerides brothers developed attachments for cultivators that replaced discs and sweeps with spyder, thinner, spinner, and weeder tools that work the soil lighter and closer to the crop. Other innovative implements include the Lilliston rolling cultivator, Rau-Kombi vibra-shank, and the Lely weeder. Ridge tilling also has its own style of cultivating equipment.
There are other approaches available when fast steel isn't appropriate. The Bartschi company has developed an effective brush weeder whose vertically mounted polypropylene brush wheels scrub between crop rows. This tool works well in wet weather and doesn't bring up new weed seeds by penetrating the soil deeply. Thermal weed control, always popular in Germany, has become better known in North America. These liquid-petroleum-powered flamers are ecologically appropriate in many situations. In citrus groves, where plastic irrigation piping prevents mechanical and flame weeding, a hot steam applicator has proved successful in trials. Electric shock machines, once popular in western sugar beet operations, are very effective on large, laser-leveled fields. There are also weeders that use mounted rubber tires to pull out established weeds. Sod crops can also be helped by mowing, harrowing, and aerating operations.
All organic weed-control methods, however, are based on timing and a healthy soil. The entire tillage system has to be timed to give the crop a competitive advantage over weeds. Some farmers eliminate fall tillage and/or delay spring tillage to plant when temperature and moisture are ideal for the quick germination and growth of crops. A healthy soil is not as prone to serious weed problems and provides a granular seedbed that ensures the rapid emergence and vigorous early growth of the crop.
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