|
Implications for Fertilizer Practices
Conventional synthetic fertilizers can dramatically affect the
balance of nutritional elements in plants. When farmers use them
excessively, these fertilizers likely create nutritional imbalances
with their large pulses of available nitrogen, which in turn compromise
crops’ resistance to insect pests.
In contrast, most organic farming practices lead to increased organic
matter and microbial activity in soils and the gradual release of
plant nutrients; in theory, this should provide more balanced nutrition
to plants. While the amount of nitrogen that is immediately available
to the crop may be lower when farmers use organic inputs, their
crops’ overall nutritional status appears to improve. By releasing
nitrogen slowly, over the course of several years, organic sources
may help render plants less attractive to pests. Organic soil fertility
practices also can supply secondary and trace elements, such as
boron, zinc, manganese and sulfur, which are occasionally lacking
in conventional farming systems that rely primarily on synthetic
sources of nitrogen, phosphorus and potassium.
If, indeed, biochemical or mineral-nutrient differences in organically
grown crops enhance resistance, this may explain — at least
in part — why lower pest levels have been reported in organic
farming systems. Observations of these lower levels support the
view that long-term management of soil organic matter leads to better
plant resistance to insect pests.
At the USDA Beltsville Agricultural Research Center, researchers
discovered a molecular basis for delayed leaf senescence and tolerance
to diseases in tomato plants grown in a hairy vetch mulch, compared
to the same crop grown on black plastic. The finding is an important
step toward a scientific rationale for alternative soil management
practices.
Probably due to regulated release of carbon and nitrogen metabolites
from hairy vetch decomposition, the cover-cropped tomato plants
showed a distinct expression of selected genes, which would lead
to a more efficient utilization and mobilization of C and N, promote
defense against disease, and enhance crop longevity. These results
confirm that in intensive conventional tomato production, the use
of legume cover crops offers advantages as a biological alternative
to commercial fertilizer, in addition to minimizing soil erosion
and loss of nutrients, enhancing water infiltration, reducing runoff,
and creating a “natural” pest-predator relationship.
Traditionally considered in isolation from one another, aboveground
and belowground components of ecosystems are now thought to be closely
linked. The (crop) plant seems to function as an integrator of the
above ground and below ground components of agroecosystems. This
holistic approach is enhancing our understanding of the role of
biodiversity at a global level. In agriculture, such close ecological
linkages between above-ground and below-ground biota constitute
a key concept on which a truly innovative ecologically based pest
management strategy can be built.
Previous Section | Top
| Next Section
|
