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  • From: "TradingPostPaul" <tradingpost@riseup.net>
  • To: livingontheland@lists.ibiblio.org
  • Subject: [Livingontheland] Maintaining soil organic matter
  • Date: Thu, 25 Jan 2007 08:32:55 -0700


Soil Quality in Vegetable and Small Fruit Production
Bulletin 898
Managing Soil Quality
Specific Tips for Vegetable Production
http://ohioline.osu.edu/b898/b898_8.html

Maintaining soil organic matter is a significant challenge in the
production of annual vegetable crops. There are two reasons for this:

* Many vegetables are short-season, low-residue crops that return small
amounts of organic material to the soil after harvest.
* Vegetable cropping systems often involve intensive tillage and
cultivation which promote rapid depletion of soil organic matter.

Carrots and onions are prime examples of low-residue crops that leave
little organic matter to replenish the soil after harvest. Potatoes produce
high amounts of organic matter per acre, but most is removed in the tubers.
Radishes and leafy crops like lettuce and spinach have short growing
seasons and return little residue even with multi-cropping. To compound the
challenge of maintaining SOM, frequent and intense cultivation are
generally used in the production of these crops.

Methods discussed in the previous section for increasing SOM—reducing
tillage, improving soil structure, and recycling excess plant
nutrients—are all suitable for vegetable crops. Application of manures,
composts, biosolids, and other organic wastes are good ways to add organic
matter. If biosolids are used, they should be low trace-metal, "clean"
sludges that can be applied to food crops with no restrictions.

Soil preparation and management operations such as preparing seedbeds,
controlling and cultivating weeds, burying crop residue (e.g., for disease
control), and building raised beds are important in vegetable production.
These operations improve certain soil conditions that otherwise limit crop
growth and development. However, each operation also accelerates the loss
of SOM by mixing and aerating the soil. And excessive tillage severely
degrades soil structure. Loss of structure makes soil prone to compaction
and related problems like reduced water infiltration and poor root growth.
Tillage operations should be selected carefully, because in some situations
growers must weigh short-term benefits to the current crop against
long-term reductions in soil quality.

Growing cover crops and preceding vegetables with high-residue rotation
crops, such as small grains and forages, can increase SOM. In addition,
many cover crops suppress weeds; legume cover crops add nitrogen; and
cereals and other grasses scavenge residual nutrients and keep them from
moving off-site. Buckwheat, sorghum-sudangrass, millets, and annual
ryegrass are useful summer cover crops that can follow early-season
vegetables or precede fall crops.

Rye and millet produce large amounts of vegetative growth, adding
potentially large amounts of organic matter. It is important to fertilize
rye cover crops or the subsequent cash crop adequately to avoid nitrogen
tie-up during decomposition. Common winter cover crops include small
grains, such as cereal rye, wheat, and oats. Oats often winter-kill and
produce much less dry matter but are a good cover crop for wet soils
because they are less likely to delay field operations in the spring. Hairy
vetch and red clover are common legume cover crops. They can be grown alone
or in grass/legume mixtures.

Many vegetable crops have relatively shallow, sparse root systems but are
well fertilized because of their high value. This combination of small root
systems and high fertilizer rates may lead to another potential
soil-quality problem—the possible movement of excess nutrients to surface
water or groundwater. Following a good soil-testing program, banding
fertilizer, splitting nitrogen applications, using fertigation, and
avoiding excess irrigation can minimize unwanted nutrient movement.

No-till alternatives have not received as much attention in vegetable crops
as in agronomic crops, especially in temperate climates with cold winters.
Yet, cover crops are used in successful no-till vegetable systems.
Transplanting into killed cover crops (e.g., tomato into hairy vetch) has
produced the best results to date. Various practices to overcome the
challenges of no-till vegetable production are being tested. For example,
seeding or transplanting into living mulches like short life-cycle medics
may allow for more timely planting and still offer the benefits of reduced
tillage. These and other practices may soon become viable alternatives,
especially in northern growing regions.

Loss of prime farmland to non-agricultural use is a major concern in many
areas. As the amount of land available for crop production and rotation is
reduced by development, it is even more important to maintain our remaining
agricultural soils at their highest possible level of quality and
productive capacity.






  • [Livingontheland] Maintaining soil organic matter, TradingPostPaul, 01/25/2007

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